Merge tag 'migration-next-pull-request' of https://gitlab.com/peterx/qemu into staging

Migartion pull request for 20240304

- Bryan's fix on multifd compression level API
- Fabiano's mapped-ram series (base + multifd only)
- Steve's amend on cpr document in qapi/

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* tag 'migration-next-pull-request' of https://gitlab.com/peterx/qemu: (27 commits)
  migration/multifd: Document two places for mapped-ram
  tests/qtest/migration: Add a multifd + mapped-ram migration test
  migration/multifd: Add mapped-ram support to fd: URI
  migration/multifd: Support incoming mapped-ram stream format
  migration/multifd: Support outgoing mapped-ram stream format
  migration/multifd: Prepare multifd sync for mapped-ram migration
  migration/multifd: Add incoming QIOChannelFile support
  migration/multifd: Add outgoing QIOChannelFile support
  migration/multifd: Add a wrapper for channels_created
  migration/multifd: Allow receiving pages without packets
  migration/multifd: Allow multifd without packets
  migration/multifd: Decouple recv method from pages
  migration/multifd: Rename MultiFDSend|RecvParams::data to compress_data
  tests/qtest/migration: Add tests for mapped-ram file-based migration
  migration/ram: Add incoming 'mapped-ram' migration
  migration/ram: Add outgoing 'mapped-ram' migration
  migration: Add mapped-ram URI compatibility check
  migration/ram: Introduce 'mapped-ram' migration capability
  migration/qemu-file: add utility methods for working with seekable channels
  io: fsync before closing a file channel
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

# Conflicts:
#	migration/ram.c

27 files changed, 1666 insertions, 160 deletions

diff --git a/docs/devel/migration/features.rst b/docs/devel/migration/features.rst
index a9acaf618e..9d1abd2587 100644
--- a/docs/devel/migration/features.rst
+++ b/docs/devel/migration/features.rst
@@ -10,3 +10,4 @@ Migration has plenty of features to support different use cases.
    dirty-limit
    vfio
    virtio
+   mapped-ram
diff --git a/docs/devel/migration/mapped-ram.rst b/docs/devel/migration/mapped-ram.rst
new file mode 100644
index 0000000000..fa4cefd9fc
--- /dev/null
+++ b/docs/devel/migration/mapped-ram.rst
@@ -0,0 +1,138 @@
+Mapped-ram
+==========
+
+Mapped-ram is a new stream format for the RAM section designed to
+supplement the existing ``file:`` migration and make it compatible
+with ``multifd``. This enables parallel migration of a guest's RAM to
+a file.
+
+The core of the feature is to ensure that RAM pages are mapped
+directly to offsets in the resulting migration file. This enables the
+``multifd`` threads to write exclusively to those offsets even if the
+guest is constantly dirtying pages (i.e. live migration). Another
+benefit is that the resulting file will have a bounded size, since
+pages which are dirtied multiple times will always go to a fixed
+location in the file, rather than constantly being added to a
+sequential stream. Having the pages at fixed offsets also allows the
+usage of O_DIRECT for save/restore of the migration stream as the
+pages are ensured to be written respecting O_DIRECT alignment
+restrictions (direct-io support not yet implemented).
+
+Usage
+-----
+
+On both source and destination, enable the ``multifd`` and
+``mapped-ram`` capabilities:
+
+    ``migrate_set_capability multifd on``
+
+    ``migrate_set_capability mapped-ram on``
+
+Use a ``file:`` URL for migration:
+
+    ``migrate file:/path/to/migration/file``
+
+Mapped-ram migration is best done non-live, i.e. by stopping the VM on
+the source side before migrating.
+
+Use-cases
+---------
+
+The mapped-ram feature was designed for use cases where the migration
+stream will be directed to a file in the filesystem and not
+immediately restored on the destination VM [#]_. These could be
+thought of as snapshots. We can further categorize them into live and
+non-live.
+
+- Non-live snapshot
+
+If the use case requires a VM to be stopped before taking a snapshot,
+that's the ideal scenario for mapped-ram migration. Not having to
+track dirty pages, the migration will write the RAM pages to the disk
+as fast as it can.
+
+Note: if a snapshot is taken of a running VM, but the VM will be
+stopped after the snapshot by the admin, then consider stopping it
+right before the snapshot to take benefit of the performance gains
+mentioned above.
+
+- Live snapshot
+
+If the use case requires that the VM keeps running during and after
+the snapshot operation, then mapped-ram migration can still be used,
+but will be less performant. Other strategies such as
+background-snapshot should be evaluated as well. One benefit of
+mapped-ram in this scenario is portability since background-snapshot
+depends on async dirty tracking (KVM_GET_DIRTY_LOG) which is not
+supported outside of Linux.
+
+.. [#] While this same effect could be obtained with the usage of
+       snapshots or the ``file:`` migration alone, mapped-ram provides
+       a performance increase for VMs with larger RAM sizes (10s to
+       100s of GiBs), specially if the VM has been stopped beforehand.
+
+RAM section format
+------------------
+
+Instead of having a sequential stream of pages that follow the
+RAMBlock headers, the dirty pages for a RAMBlock follow its header
+instead. This ensures that each RAM page has a fixed offset in the
+resulting migration file.
+
+A bitmap is introduced to track which pages have been written in the
+migration file. Pages are written at a fixed location for every
+ramblock. Zero pages are ignored as they'd be zero in the destination
+migration as well.
+
+::
+
+ Without mapped-ram:                  With mapped-ram:
+
+ ---------------------               --------------------------------
+ | ramblock 1 header |               | ramblock 1 header            |
+ ---------------------               --------------------------------
+ | ramblock 2 header |               | ramblock 1 mapped-ram header |
+ ---------------------               --------------------------------
+ | ...               |               | padding to next 1MB boundary |
+ ---------------------               | ...                          |
+ | ramblock n header |               --------------------------------
+ ---------------------               | ramblock 1 pages             |
+ | RAM_SAVE_FLAG_EOS |               | ...                          |
+ ---------------------               --------------------------------
+ | stream of pages   |               | ramblock 2 header            |
+ | (iter 1)          |               --------------------------------
+ | ...               |               | ramblock 2 mapped-ram header |
+ ---------------------               --------------------------------
+ | RAM_SAVE_FLAG_EOS |               | padding to next 1MB boundary |
+ ---------------------               | ...                          |
+ | stream of pages   |               --------------------------------
+ | (iter 2)          |               | ramblock 2 pages             |
+ | ...               |               | ...                          |
+ ---------------------               --------------------------------
+ | ...               |               | ...                          |
+ ---------------------               --------------------------------
+                                     | RAM_SAVE_FLAG_EOS            |
+                                     --------------------------------
+                                     | ...                          |
+                                     --------------------------------
+
+where:
+ - ramblock header: the generic information for a ramblock, such as
+   idstr, used_len, etc.
+
+ - ramblock mapped-ram header: the information added by this feature:
+   bitmap of pages written, bitmap size and offset of pages in the
+   migration file.
+
+Restrictions
+------------
+
+Since pages are written to their relative offsets and out of order
+(due to the memory dirtying patterns), streaming channels such as
+sockets are not supported. A seekable channel such as a file is
+required. This can be verified in the QIOChannel by the presence of
+the QIO_CHANNEL_FEATURE_SEEKABLE.
+
+The improvements brought by this feature apply only to guest physical
+RAM. Other types of memory such as VRAM are migrated as part of device
+states.
diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h
index 3eb79723c6..848915ea5b 100644
--- a/include/exec/ramblock.h
+++ b/include/exec/ramblock.h
@@ -44,6 +44,19 @@ struct RAMBlock {
     size_t page_size;
     /* dirty bitmap used during migration */
     unsigned long *bmap;
+
+    /*
+     * Below fields are only used by mapped-ram migration
+     */
+    /* bitmap of pages present in the migration file */
+    unsigned long *file_bmap;
+    /*
+     * offset in the file pages belonging to this ramblock are saved,
+     * used only during migration to a file.
+     */
+    off_t bitmap_offset;
+    uint64_t pages_offset;
+
     /* bitmap of already received pages in postcopy */
     unsigned long *receivedmap;
 
diff --git a/include/io/channel.h b/include/io/channel.h
index 5f9dbaab65..7986c49c71 100644
--- a/include/io/channel.h
+++ b/include/io/channel.h
@@ -44,6 +44,7 @@ enum QIOChannelFeature {
     QIO_CHANNEL_FEATURE_LISTEN,
     QIO_CHANNEL_FEATURE_WRITE_ZERO_COPY,
     QIO_CHANNEL_FEATURE_READ_MSG_PEEK,
+    QIO_CHANNEL_FEATURE_SEEKABLE,
 };
 
 
@@ -130,6 +131,16 @@ struct QIOChannelClass {
                            Error **errp);
 
     /* Optional callbacks */
+    ssize_t (*io_pwritev)(QIOChannel *ioc,
+                          const struct iovec *iov,
+                          size_t niov,
+                          off_t offset,
+                          Error **errp);
+    ssize_t (*io_preadv)(QIOChannel *ioc,
+                         const struct iovec *iov,
+                         size_t niov,
+                         off_t offset,
+                         Error **errp);
     int (*io_shutdown)(QIOChannel *ioc,
                        QIOChannelShutdown how,
                        Error **errp);
@@ -529,6 +540,78 @@ int qio_channel_close(QIOChannel *ioc,
                       Error **errp);
 
 /**
+ * qio_channel_pwritev
+ * @ioc: the channel object
+ * @iov: the array of memory regions to write data from
+ * @niov: the length of the @iov array
+ * @offset: offset in the channel where writes should begin
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Not all implementations will support this facility, so may report
+ * an error. To avoid errors, the caller may check for the feature
+ * flag QIO_CHANNEL_FEATURE_SEEKABLE prior to calling this method.
+ *
+ * Behaves as qio_channel_writev_full, apart from not supporting
+ * sending of file handles as well as beginning the write at the
+ * passed @offset
+ *
+ */
+ssize_t qio_channel_pwritev(QIOChannel *ioc, const struct iovec *iov,
+                            size_t niov, off_t offset, Error **errp);
+
+/**
+ * qio_channel_pwrite
+ * @ioc: the channel object
+ * @buf: the memory region to write data into
+ * @buflen: the number of bytes to @buf
+ * @offset: offset in the channel where writes should begin
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Not all implementations will support this facility, so may report
+ * an error. To avoid errors, the caller may check for the feature
+ * flag QIO_CHANNEL_FEATURE_SEEKABLE prior to calling this method.
+ *
+ */
+ssize_t qio_channel_pwrite(QIOChannel *ioc, char *buf, size_t buflen,
+                           off_t offset, Error **errp);
+
+/**
+ * qio_channel_preadv
+ * @ioc: the channel object
+ * @iov: the array of memory regions to read data into
+ * @niov: the length of the @iov array
+ * @offset: offset in the channel where writes should begin
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Not all implementations will support this facility, so may report
+ * an error.  To avoid errors, the caller may check for the feature
+ * flag QIO_CHANNEL_FEATURE_SEEKABLE prior to calling this method.
+ *
+ * Behaves as qio_channel_readv_full, apart from not supporting
+ * receiving of file handles as well as beginning the read at the
+ * passed @offset
+ *
+ */
+ssize_t qio_channel_preadv(QIOChannel *ioc, const struct iovec *iov,
+                           size_t niov, off_t offset, Error **errp);
+
+/**
+ * qio_channel_pread
+ * @ioc: the channel object
+ * @buf: the memory region to write data into
+ * @buflen: the number of bytes to @buf
+ * @offset: offset in the channel where writes should begin
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Not all implementations will support this facility, so may report
+ * an error.  To avoid errors, the caller may check for the feature
+ * flag QIO_CHANNEL_FEATURE_SEEKABLE prior to calling this method.
+ *
+ */
+ssize_t qio_channel_pread(QIOChannel *ioc, char *buf, size_t buflen,
+                          off_t offset, Error **errp);
+
+/**
  * qio_channel_shutdown:
  * @ioc: the channel object
  * @how: the direction to shutdown
diff --git a/include/migration/qemu-file-types.h b/include/migration/qemu-file-types.h
index 9ba163f333..adec5abc07 100644
--- a/include/migration/qemu-file-types.h
+++ b/include/migration/qemu-file-types.h
@@ -50,6 +50,8 @@ unsigned int qemu_get_be16(QEMUFile *f);
 unsigned int qemu_get_be32(QEMUFile *f);
 uint64_t qemu_get_be64(QEMUFile *f);
 
+bool qemu_file_is_seekable(QEMUFile *f);
+
 static inline void qemu_put_be64s(QEMUFile *f, const uint64_t *pv)
 {
     qemu_put_be64(f, *pv);
diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h
index cb3526d1f4..2c0a2fe751 100644
--- a/include/qemu/bitops.h
+++ b/include/qemu/bitops.h
@@ -68,6 +68,19 @@ static inline void clear_bit(long nr, unsigned long *addr)
 }
 
 /**
+ * clear_bit_atomic - Clears a bit in memory atomically
+ * @nr: Bit to clear
+ * @addr: Address to start counting from
+ */
+static inline void clear_bit_atomic(long nr, unsigned long *addr)
+{
+    unsigned long mask = BIT_MASK(nr);
+    unsigned long *p = addr + BIT_WORD(nr);
+
+    return qatomic_and(p, ~mask);
+}
+
+/**
  * change_bit - Toggle a bit in memory
  * @nr: Bit to change
  * @addr: Address to start counting from
diff --git a/io/channel-file.c b/io/channel-file.c
index 4a12c61886..d4706fa592 100644
--- a/io/channel-file.c
+++ b/io/channel-file.c
@@ -36,6 +36,10 @@ qio_channel_file_new_fd(int fd)
 
     ioc->fd = fd;
 
+    if (lseek(fd, 0, SEEK_CUR) != (off_t)-1) {
+        qio_channel_set_feature(QIO_CHANNEL(ioc), QIO_CHANNEL_FEATURE_SEEKABLE);
+    }
+
     trace_qio_channel_file_new_fd(ioc, fd);
 
     return ioc;
@@ -60,6 +64,10 @@ qio_channel_file_new_path(const char *path,
         return NULL;
     }
 
+    if (lseek(ioc->fd, 0, SEEK_CUR) != (off_t)-1) {
+        qio_channel_set_feature(QIO_CHANNEL(ioc), QIO_CHANNEL_FEATURE_SEEKABLE);
+    }
+
     trace_qio_channel_file_new_path(ioc, path, flags, mode, ioc->fd);
 
     return ioc;
@@ -138,6 +146,58 @@ static ssize_t qio_channel_file_writev(QIOChannel *ioc,
     return ret;
 }
 
+#ifdef CONFIG_PREADV
+static ssize_t qio_channel_file_preadv(QIOChannel *ioc,
+                                       const struct iovec *iov,
+                                       size_t niov,
+                                       off_t offset,
+                                       Error **errp)
+{
+    QIOChannelFile *fioc = QIO_CHANNEL_FILE(ioc);
+    ssize_t ret;
+
+ retry:
+    ret = preadv(fioc->fd, iov, niov, offset);
+    if (ret < 0) {
+        if (errno == EAGAIN) {
+            return QIO_CHANNEL_ERR_BLOCK;
+        }
+        if (errno == EINTR) {
+            goto retry;
+        }
+
+        error_setg_errno(errp, errno, "Unable to read from file");
+        return -1;
+    }
+
+    return ret;
+}
+
+static ssize_t qio_channel_file_pwritev(QIOChannel *ioc,
+                                        const struct iovec *iov,
+                                        size_t niov,
+                                        off_t offset,
+                                        Error **errp)
+{
+    QIOChannelFile *fioc = QIO_CHANNEL_FILE(ioc);
+    ssize_t ret;
+
+ retry:
+    ret = pwritev(fioc->fd, iov, niov, offset);
+    if (ret <= 0) {
+        if (errno == EAGAIN) {
+            return QIO_CHANNEL_ERR_BLOCK;
+        }
+        if (errno == EINTR) {
+            goto retry;
+        }
+        error_setg_errno(errp, errno, "Unable to write to file");
+        return -1;
+    }
+    return ret;
+}
+#endif /* CONFIG_PREADV */
+
 static int qio_channel_file_set_blocking(QIOChannel *ioc,
                                          bool enabled,
                                          Error **errp)
@@ -182,6 +242,11 @@ static int qio_channel_file_close(QIOChannel *ioc,
 {
     QIOChannelFile *fioc = QIO_CHANNEL_FILE(ioc);
 
+    if (qemu_fdatasync(fioc->fd) < 0) {
+        error_setg_errno(errp, errno,
+                         "Unable to synchronize file data with storage device");
+        return -1;
+    }
     if (qemu_close(fioc->fd) < 0) {
         error_setg_errno(errp, errno,
                          "Unable to close file");
@@ -223,6 +288,10 @@ static void qio_channel_file_class_init(ObjectClass *klass,
     ioc_klass->io_writev = qio_channel_file_writev;
     ioc_klass->io_readv = qio_channel_file_readv;
     ioc_klass->io_set_blocking = qio_channel_file_set_blocking;
+#ifdef CONFIG_PREADV
+    ioc_klass->io_pwritev = qio_channel_file_pwritev;
+    ioc_klass->io_preadv = qio_channel_file_preadv;
+#endif
     ioc_klass->io_seek = qio_channel_file_seek;
     ioc_klass->io_close = qio_channel_file_close;
     ioc_klass->io_create_watch = qio_channel_file_create_watch;
diff --git a/io/channel.c b/io/channel.c
index 86c5834510..a1f12f8e90 100644
--- a/io/channel.c
+++ b/io/channel.c
@@ -454,6 +454,64 @@ GSource *qio_channel_add_watch_source(QIOChannel *ioc,
 }
 
 
+ssize_t qio_channel_pwritev(QIOChannel *ioc, const struct iovec *iov,
+                            size_t niov, off_t offset, Error **errp)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+    if (!klass->io_pwritev) {
+        error_setg(errp, "Channel does not support pwritev");
+        return -1;
+    }
+
+    if (!qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_SEEKABLE)) {
+        error_setg_errno(errp, EINVAL, "Requested channel is not seekable");
+        return -1;
+    }
+
+    return klass->io_pwritev(ioc, iov, niov, offset, errp);
+}
+
+ssize_t qio_channel_pwrite(QIOChannel *ioc, char *buf, size_t buflen,
+                           off_t offset, Error **errp)
+{
+    struct iovec iov = {
+        .iov_base = buf,
+        .iov_len = buflen
+    };
+
+    return qio_channel_pwritev(ioc, &iov, 1, offset, errp);
+}
+
+ssize_t qio_channel_preadv(QIOChannel *ioc, const struct iovec *iov,
+                           size_t niov, off_t offset, Error **errp)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+    if (!klass->io_preadv) {
+        error_setg(errp, "Channel does not support preadv");
+        return -1;
+    }
+
+    if (!qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_SEEKABLE)) {
+        error_setg_errno(errp, EINVAL, "Requested channel is not seekable");
+        return -1;
+    }
+
+    return klass->io_preadv(ioc, iov, niov, offset, errp);
+}
+
+ssize_t qio_channel_pread(QIOChannel *ioc, char *buf, size_t buflen,
+                          off_t offset, Error **errp)
+{
+    struct iovec iov = {
+        .iov_base = buf,
+        .iov_len = buflen
+    };
+
+    return qio_channel_preadv(ioc, &iov, 1, offset, errp);
+}
+
 int qio_channel_shutdown(QIOChannel *ioc,
                          QIOChannelShutdown how,
                          Error **errp)
diff --git a/migration/fd.c b/migration/fd.c
index 0eb677dcae..d4ae72d132 100644
--- a/migration/fd.c
+++ b/migration/fd.c
@@ -15,18 +15,41 @@
  */
 
 #include "qemu/osdep.h"
+#include "qapi/error.h"
 #include "channel.h"
 #include "fd.h"
 #include "migration.h"
 #include "monitor/monitor.h"
+#include "io/channel-file.h"
 #include "io/channel-util.h"
+#include "options.h"
 #include "trace.h"
 
 
+static struct FdOutgoingArgs {
+    int fd;
+} outgoing_args;
+
+int fd_args_get_fd(void)
+{
+    return outgoing_args.fd;
+}
+
+void fd_cleanup_outgoing_migration(void)
+{
+    if (outgoing_args.fd > 0) {
+        close(outgoing_args.fd);
+        outgoing_args.fd = -1;
+    }
+}
+
 void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
 {
     QIOChannel *ioc;
     int fd = monitor_get_fd(monitor_cur(), fdname, errp);
+
+    outgoing_args.fd = -1;
+
     if (fd == -1) {
         return;
     }
@@ -38,6 +61,8 @@ void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **
         return;
     }
 
+    outgoing_args.fd = fd;
+
     qio_channel_set_name(ioc, "migration-fd-outgoing");
     migration_channel_connect(s, ioc, NULL, NULL);
     object_unref(OBJECT(ioc));
@@ -73,4 +98,23 @@ void fd_start_incoming_migration(const char *fdname, Error **errp)
                                fd_accept_incoming_migration,
                                NULL, NULL,
                                g_main_context_get_thread_default());
+
+    if (migrate_multifd()) {
+        int channels = migrate_multifd_channels();
+
+        while (channels--) {
+            ioc = QIO_CHANNEL(qio_channel_file_new_fd(dup(fd)));
+
+            if (QIO_CHANNEL_FILE(ioc)->fd == -1) {
+                error_setg(errp, "Failed to duplicate fd %d", fd);
+                return;
+            }
+
+            qio_channel_set_name(ioc, "migration-fd-incoming");
+            qio_channel_add_watch_full(ioc, G_IO_IN,
+                                       fd_accept_incoming_migration,
+                                       NULL, NULL,
+                                       g_main_context_get_thread_default());
+        }
+    }
 }
diff --git a/migration/fd.h b/migration/fd.h
index b901bc014e..0c0a18d9e7 100644
--- a/migration/fd.h
+++ b/migration/fd.h
@@ -20,4 +20,6 @@ void fd_start_incoming_migration(const char *fdname, Error **errp);
 
 void fd_start_outgoing_migration(MigrationState *s, const char *fdname,
                                  Error **errp);
+void fd_cleanup_outgoing_migration(void);
+int fd_args_get_fd(void);
 #endif
diff --git a/migration/file.c b/migration/file.c
index 5d4975f43e..164b079966 100644
--- a/migration/file.c
+++ b/migration/file.c
@@ -6,17 +6,25 @@
  */
 
 #include "qemu/osdep.h"
+#include "exec/ramblock.h"
 #include "qemu/cutils.h"
+#include "qemu/error-report.h"
 #include "qapi/error.h"
 #include "channel.h"
+#include "fd.h"
 #include "file.h"
 #include "migration.h"
 #include "io/channel-file.h"
 #include "io/channel-util.h"
+#include "options.h"
 #include "trace.h"
 
 #define OFFSET_OPTION ",offset="
 
+static struct FileOutgoingArgs {
+    char *fname;
+} outgoing_args;
+
 /* Remove the offset option from @filespec and return it in @offsetp. */
 
 int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp)
@@ -36,6 +44,41 @@ int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp)
     return 0;
 }
 
+void file_cleanup_outgoing_migration(void)
+{
+    g_free(outgoing_args.fname);
+    outgoing_args.fname = NULL;
+}
+
+bool file_send_channel_create(gpointer opaque, Error **errp)
+{
+    QIOChannelFile *ioc;
+    int flags = O_WRONLY;
+    bool ret = false;
+    int fd = fd_args_get_fd();
+
+    if (fd && fd != -1) {
+        ioc = qio_channel_file_new_fd(dup(fd));
+    } else {
+        ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, errp);
+        if (!ioc) {
+            goto out;
+        }
+    }
+
+    multifd_channel_connect(opaque, QIO_CHANNEL(ioc));
+    ret = true;
+
+out:
+    /*
+     * File channel creation is synchronous. However posting this
+     * semaphore here is simpler than adding a special case.
+     */
+    multifd_send_channel_created();
+
+    return ret;
+}
+
 void file_start_outgoing_migration(MigrationState *s,
                                    FileMigrationArgs *file_args, Error **errp)
 {
@@ -52,6 +95,8 @@ void file_start_outgoing_migration(MigrationState *s,
         return;
     }
 
+    outgoing_args.fname = g_strdup(filename);
+
     ioc = QIO_CHANNEL(fioc);
     if (offset && qio_channel_io_seek(ioc, offset, SEEK_SET, errp) < 0) {
         return;
@@ -74,7 +119,8 @@ void file_start_incoming_migration(FileMigrationArgs *file_args, Error **errp)
     g_autofree char *filename = g_strdup(file_args->filename);
     QIOChannelFile *fioc = NULL;
     uint64_t offset = file_args->offset;
-    QIOChannel *ioc;
+    int channels = 1;
+    int i = 0;
 
     trace_migration_file_incoming(filename);
 
@@ -83,13 +129,100 @@ void file_start_incoming_migration(FileMigrationArgs *file_args, Error **errp)
         return;
     }
 
-    ioc = QIO_CHANNEL(fioc);
-    if (offset && qio_channel_io_seek(ioc, offset, SEEK_SET, errp) < 0) {
+    if (offset &&
+        qio_channel_io_seek(QIO_CHANNEL(fioc), offset, SEEK_SET, errp) < 0) {
         return;
     }
-    qio_channel_set_name(QIO_CHANNEL(ioc), "migration-file-incoming");
-    qio_channel_add_watch_full(ioc, G_IO_IN,
-                               file_accept_incoming_migration,
-                               NULL, NULL,
-                               g_main_context_get_thread_default());
+
+    if (migrate_multifd()) {
+        channels += migrate_multifd_channels();
+    }
+
+    do {
+        QIOChannel *ioc = QIO_CHANNEL(fioc);
+
+        qio_channel_set_name(ioc, "migration-file-incoming");
+        qio_channel_add_watch_full(ioc, G_IO_IN,
+                                   file_accept_incoming_migration,
+                                   NULL, NULL,
+                                   g_main_context_get_thread_default());
+
+        fioc = qio_channel_file_new_fd(dup(fioc->fd));
+
+        if (!fioc || fioc->fd == -1) {
+            error_setg(errp, "Error creating migration incoming channel");
+            break;
+        }
+    } while (++i < channels);
+}
+
+int file_write_ramblock_iov(QIOChannel *ioc, const struct iovec *iov,
+                            int niov, RAMBlock *block, Error **errp)
+{
+    ssize_t ret = -1;
+    int i, slice_idx, slice_num;
+    uintptr_t base, next, offset;
+    size_t len;
+
+    slice_idx = 0;
+    slice_num = 1;
+
+    /*
+     * If the iov array doesn't have contiguous elements, we need to
+     * split it in slices because we only have one file offset for the
+     * whole iov. Do this here so callers don't need to break the iov
+     * array themselves.
+     */
+    for (i = 0; i < niov; i++, slice_num++) {
+        base = (uintptr_t) iov[i].iov_base;
+
+        if (i != niov - 1) {
+            len = iov[i].iov_len;
+            next = (uintptr_t) iov[i + 1].iov_base;
+
+            if (base + len == next) {
+                continue;
+            }
+        }
+
+        /*
+         * Use the offset of the first element of the segment that
+         * we're sending.
+         */
+        offset = (uintptr_t) iov[slice_idx].iov_base - (uintptr_t) block->host;
+        if (offset >= block->used_length) {
+            error_setg(errp, "offset " RAM_ADDR_FMT
+                       "outside of ramblock %s range", offset, block->idstr);
+            ret = -1;
+            break;
+        }
+
+        ret = qio_channel_pwritev(ioc, &iov[slice_idx], slice_num,
+                                  block->pages_offset + offset, errp);
+        if (ret < 0) {
+            break;
+        }
+
+        slice_idx += slice_num;
+        slice_num = 0;
+    }
+
+    return (ret < 0) ? ret : 0;
+}
+
+int multifd_file_recv_data(MultiFDRecvParams *p, Error **errp)
+{
+    MultiFDRecvData *data = p->data;
+    size_t ret;
+
+    ret = qio_channel_pread(p->c, (char *) data->opaque,
+                            data->size, data->file_offset, errp);
+    if (ret != data->size) {
+        error_prepend(errp,
+                      "multifd recv (%u): read 0x%zx, expected 0x%zx",
+                      p->id, ret, data->size);
+        return -1;
+    }
+
+    return 0;
 }
diff --git a/migration/file.h b/migration/file.h
index 37d6a08bfc..9f71e87f74 100644
--- a/migration/file.h
+++ b/migration/file.h
@@ -9,10 +9,18 @@
 #define QEMU_MIGRATION_FILE_H
 
 #include "qapi/qapi-types-migration.h"
+#include "io/task.h"
+#include "channel.h"
+#include "multifd.h"
 
 void file_start_incoming_migration(FileMigrationArgs *file_args, Error **errp);
 
 void file_start_outgoing_migration(MigrationState *s,
                                    FileMigrationArgs *file_args, Error **errp);
 int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp);
+void file_cleanup_outgoing_migration(void);
+bool file_send_channel_create(gpointer opaque, Error **errp);
+int file_write_ramblock_iov(QIOChannel *ioc, const struct iovec *iov,
+                            int niov, RAMBlock *block, Error **errp);
+int multifd_file_recv_data(MultiFDRecvParams *p, Error **errp);
 #endif
diff --git a/migration/migration.c b/migration/migration.c
index bab68bcbef..a49fcd53ee 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -140,9 +140,38 @@ static bool transport_supports_multi_channels(MigrationAddress *addr)
     if (addr->transport == MIGRATION_ADDRESS_TYPE_SOCKET) {
         SocketAddress *saddr = &addr->u.socket;
 
-        return saddr->type == SOCKET_ADDRESS_TYPE_INET ||
-               saddr->type == SOCKET_ADDRESS_TYPE_UNIX ||
-               saddr->type == SOCKET_ADDRESS_TYPE_VSOCK;
+        if (saddr->type == SOCKET_ADDRESS_TYPE_FD) {
+            return migrate_mapped_ram();
+        }
+
+        return (saddr->type == SOCKET_ADDRESS_TYPE_INET ||
+                saddr->type == SOCKET_ADDRESS_TYPE_UNIX ||
+                saddr->type == SOCKET_ADDRESS_TYPE_VSOCK);
+    } else if (addr->transport == MIGRATION_ADDRESS_TYPE_FILE) {
+        return migrate_mapped_ram();
+    } else {
+        return false;
+    }
+}
+
+static bool migration_needs_seekable_channel(void)
+{
+    return migrate_mapped_ram();
+}
+
+static bool transport_supports_seeking(MigrationAddress *addr)
+{
+    if (addr->transport == MIGRATION_ADDRESS_TYPE_FILE) {
+        return true;
+    }
+
+    /*
+     * At this point, the user might not yet have passed the file
+     * descriptor to QEMU, so we cannot know for sure whether it
+     * refers to a plain file or a socket. Let it through anyway.
+     */
+    if (addr->transport == MIGRATION_ADDRESS_TYPE_SOCKET) {
+        return addr->u.socket.type == SOCKET_ADDRESS_TYPE_FD;
     }
 
     return false;
@@ -152,6 +181,12 @@ static bool
 migration_channels_and_transport_compatible(MigrationAddress *addr,
                                             Error **errp)
 {
+    if (migration_needs_seekable_channel() &&
+        !transport_supports_seeking(addr)) {
+        error_setg(errp, "Migration requires seekable transport (e.g. file)");
+        return false;
+    }
+
     if (migration_needs_multiple_sockets() &&
         !transport_supports_multi_channels(addr)) {
         error_setg(errp, "Migration requires multi-channel URIs (e.g. tcp)");
@@ -881,7 +916,8 @@ void migration_ioc_process_incoming(QIOChannel *ioc, Error **errp)
     uint32_t channel_magic = 0;
     int ret = 0;
 
-    if (migrate_multifd() && !migrate_postcopy_ram() &&
+    if (migrate_multifd() && !migrate_mapped_ram() &&
+        !migrate_postcopy_ram() &&
         qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_READ_MSG_PEEK)) {
         /*
          * With multiple channels, it is possible that we receive channels
@@ -1950,6 +1986,18 @@ static bool migrate_prepare(MigrationState *s, bool blk, bool blk_inc,
         return false;
     }
 
+    if (migrate_mapped_ram()) {
+        if (migrate_tls()) {
+            error_setg(errp, "Cannot use TLS with mapped-ram");
+            return false;
+        }
+
+        if (migrate_multifd_compression()) {
+            error_setg(errp, "Cannot use compression with mapped-ram");
+            return false;
+        }
+    }
+
     if (migrate_mode_is_cpr(s)) {
         const char *conflict = NULL;
 
diff --git a/migration/multifd-zlib.c b/migration/multifd-zlib.c
index 012e3bdea1..6120faad65 100644
--- a/migration/multifd-zlib.c
+++ b/migration/multifd-zlib.c
@@ -69,7 +69,7 @@ static int zlib_send_setup(MultiFDSendParams *p, Error **errp)
         err_msg = "out of memory for buf";
         goto err_free_zbuff;
     }
-    p->data = z;
+    p->compress_data = z;
     return 0;
 
 err_free_zbuff:
@@ -92,15 +92,15 @@ err_free_z:
  */
 static void zlib_send_cleanup(MultiFDSendParams *p, Error **errp)
 {
-    struct zlib_data *z = p->data;
+    struct zlib_data *z = p->compress_data;
 
     deflateEnd(&z->zs);
     g_free(z->zbuff);
     z->zbuff = NULL;
     g_free(z->buf);
     z->buf = NULL;
-    g_free(p->data);
-    p->data = NULL;
+    g_free(p->compress_data);
+    p->compress_data = NULL;
 }
 
 /**
@@ -117,7 +117,7 @@ static void zlib_send_cleanup(MultiFDSendParams *p, Error **errp)
 static int zlib_send_prepare(MultiFDSendParams *p, Error **errp)
 {
     MultiFDPages_t *pages = p->pages;
-    struct zlib_data *z = p->data;
+    struct zlib_data *z = p->compress_data;
     z_stream *zs = &z->zs;
     uint32_t out_size = 0;
     int ret;
@@ -194,7 +194,7 @@ static int zlib_recv_setup(MultiFDRecvParams *p, Error **errp)
     struct zlib_data *z = g_new0(struct zlib_data, 1);
     z_stream *zs = &z->zs;
 
-    p->data = z;
+    p->compress_data = z;
     zs->zalloc = Z_NULL;
     zs->zfree = Z_NULL;
     zs->opaque = Z_NULL;
@@ -224,17 +224,17 @@ static int zlib_recv_setup(MultiFDRecvParams *p, Error **errp)
  */
 static void zlib_recv_cleanup(MultiFDRecvParams *p)
 {
-    struct zlib_data *z = p->data;
+    struct zlib_data *z = p->compress_data;
 
     inflateEnd(&z->zs);
     g_free(z->zbuff);
     z->zbuff = NULL;
-    g_free(p->data);
-    p->data = NULL;
+    g_free(p->compress_data);
+    p->compress_data = NULL;
 }
 
 /**
- * zlib_recv_pages: read the data from the channel into actual pages
+ * zlib_recv: read the data from the channel into actual pages
  *
  * Read the compressed buffer, and uncompress it into the actual
  * pages.
@@ -244,9 +244,9 @@ static void zlib_recv_cleanup(MultiFDRecvParams *p)
  * @p: Params for the channel that we are using
  * @errp: pointer to an error
  */
-static int zlib_recv_pages(MultiFDRecvParams *p, Error **errp)
+static int zlib_recv(MultiFDRecvParams *p, Error **errp)
 {
-    struct zlib_data *z = p->data;
+    struct zlib_data *z = p->compress_data;
     z_stream *zs = &z->zs;
     uint32_t in_size = p->next_packet_size;
     /* we measure the change of total_out */
@@ -319,7 +319,7 @@ static MultiFDMethods multifd_zlib_ops = {
     .send_prepare = zlib_send_prepare,
     .recv_setup = zlib_recv_setup,
     .recv_cleanup = zlib_recv_cleanup,
-    .recv_pages = zlib_recv_pages
+    .recv = zlib_recv
 };
 
 static void multifd_zlib_register(void)
diff --git a/migration/multifd-zstd.c b/migration/multifd-zstd.c
index dc8fe43e94..cac236833d 100644
--- a/migration/multifd-zstd.c
+++ b/migration/multifd-zstd.c
@@ -52,7 +52,7 @@ static int zstd_send_setup(MultiFDSendParams *p, Error **errp)
     struct zstd_data *z = g_new0(struct zstd_data, 1);
     int res;
 
-    p->data = z;
+    p->compress_data = z;
     z->zcs = ZSTD_createCStream();
     if (!z->zcs) {
         g_free(z);
@@ -90,14 +90,14 @@ static int zstd_send_setup(MultiFDSendParams *p, Error **errp)
  */
 static void zstd_send_cleanup(MultiFDSendParams *p, Error **errp)
 {
-    struct zstd_data *z = p->data;
+    struct zstd_data *z = p->compress_data;
 
     ZSTD_freeCStream(z->zcs);
     z->zcs = NULL;
     g_free(z->zbuff);
     z->zbuff = NULL;
-    g_free(p->data);
-    p->data = NULL;
+    g_free(p->compress_data);
+    p->compress_data = NULL;
 }
 
 /**
@@ -114,7 +114,7 @@ static void zstd_send_cleanup(MultiFDSendParams *p, Error **errp)
 static int zstd_send_prepare(MultiFDSendParams *p, Error **errp)
 {
     MultiFDPages_t *pages = p->pages;
-    struct zstd_data *z = p->data;
+    struct zstd_data *z = p->compress_data;
     int ret;
     uint32_t i;
 
@@ -183,7 +183,7 @@ static int zstd_recv_setup(MultiFDRecvParams *p, Error **errp)
     struct zstd_data *z = g_new0(struct zstd_data, 1);
     int ret;
 
-    p->data = z;
+    p->compress_data = z;
     z->zds = ZSTD_createDStream();
     if (!z->zds) {
         g_free(z);
@@ -221,18 +221,18 @@ static int zstd_recv_setup(MultiFDRecvParams *p, Error **errp)
  */
 static void zstd_recv_cleanup(MultiFDRecvParams *p)
 {
-    struct zstd_data *z = p->data;
+    struct zstd_data *z = p->compress_data;
 
     ZSTD_freeDStream(z->zds);
     z->zds = NULL;
     g_free(z->zbuff);
     z->zbuff = NULL;
-    g_free(p->data);
-    p->data = NULL;
+    g_free(p->compress_data);
+    p->compress_data = NULL;
 }
 
 /**
- * zstd_recv_pages: read the data from the channel into actual pages
+ * zstd_recv: read the data from the channel into actual pages
  *
  * Read the compressed buffer, and uncompress it into the actual
  * pages.
@@ -242,13 +242,13 @@ static void zstd_recv_cleanup(MultiFDRecvParams *p)
  * @p: Params for the channel that we are using
  * @errp: pointer to an error
  */
-static int zstd_recv_pages(MultiFDRecvParams *p, Error **errp)
+static int zstd_recv(MultiFDRecvParams *p, Error **errp)
 {
     uint32_t in_size = p->next_packet_size;
     uint32_t out_size = 0;
     uint32_t expected_size = p->normal_num * p->page_size;
     uint32_t flags = p->flags & MULTIFD_FLAG_COMPRESSION_MASK;
-    struct zstd_data *z = p->data;
+    struct zstd_data *z = p->compress_data;
     int ret;
     int i;
 
@@ -310,7 +310,7 @@ static MultiFDMethods multifd_zstd_ops = {
     .send_prepare = zstd_send_prepare,
     .recv_setup = zstd_recv_setup,
     .recv_cleanup = zstd_recv_cleanup,
-    .recv_pages = zstd_recv_pages
+    .recv = zstd_recv
 };
 
 static void multifd_zstd_register(void)
diff --git a/migration/multifd.c b/migration/multifd.c
index 6c07f19af1..d4a44da559 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -17,7 +17,8 @@
 #include "exec/ramblock.h"
 #include "qemu/error-report.h"
 #include "qapi/error.h"
-#include "ram.h"
+#include "fd.h"
+#include "file.h"
 #include "migration.h"
 #include "migration-stats.h"
 #include "socket.h"
@@ -28,6 +29,7 @@
 #include "threadinfo.h"
 #include "options.h"
 #include "qemu/yank.h"
+#include "io/channel-file.h"
 #include "io/channel-socket.h"
 #include "yank_functions.h"
 
@@ -81,9 +83,13 @@ struct {
 
 struct {
     MultiFDRecvParams *params;
+    MultiFDRecvData *data;
     /* number of created threads */
     int count;
-    /* syncs main thread and channels */
+    /*
+     * This is always posted by the recv threads, the migration thread
+     * uses it to wait for recv threads to finish assigned tasks.
+     */
     QemuSemaphore sem_sync;
     /* global number of generated multifd packets */
     uint64_t packet_num;
@@ -92,6 +98,27 @@ struct {
     MultiFDMethods *ops;
 } *multifd_recv_state;
 
+static bool multifd_use_packets(void)
+{
+    return !migrate_mapped_ram();
+}
+
+void multifd_send_channel_created(void)
+{
+    qemu_sem_post(&multifd_send_state->channels_created);
+}
+
+static void multifd_set_file_bitmap(MultiFDSendParams *p)
+{
+    MultiFDPages_t *pages = p->pages;
+
+    assert(pages->block);
+
+    for (int i = 0; i < p->pages->num; i++) {
+        ramblock_set_file_bmap_atomic(pages->block, pages->offset[i]);
+    }
+}
+
 /* Multifd without compression */
 
 /**
@@ -122,6 +149,19 @@ static void nocomp_send_cleanup(MultiFDSendParams *p, Error **errp)
     return;
 }
 
+static void multifd_send_prepare_iovs(MultiFDSendParams *p)
+{
+    MultiFDPages_t *pages = p->pages;
+
+    for (int i = 0; i < pages->num; i++) {
+        p->iov[p->iovs_num].iov_base = pages->block->host + pages->offset[i];
+        p->iov[p->iovs_num].iov_len = p->page_size;
+        p->iovs_num++;
+    }
+
+    p->next_packet_size = pages->num * p->page_size;
+}
+
 /**
  * nocomp_send_prepare: prepare date to be able to send
  *
@@ -136,9 +176,15 @@ static void nocomp_send_cleanup(MultiFDSendParams *p, Error **errp)
 static int nocomp_send_prepare(MultiFDSendParams *p, Error **errp)
 {
     bool use_zero_copy_send = migrate_zero_copy_send();
-    MultiFDPages_t *pages = p->pages;
     int ret;
 
+    if (!multifd_use_packets()) {
+        multifd_send_prepare_iovs(p);
+        multifd_set_file_bitmap(p);
+
+        return 0;
+    }
+
     if (!use_zero_copy_send) {
         /*
          * Only !zerocopy needs the header in IOV; zerocopy will
@@ -147,13 +193,7 @@ static int nocomp_send_prepare(MultiFDSendParams *p, Error **errp)
         multifd_send_prepare_header(p);
     }
 
-    for (int i = 0; i < pages->num; i++) {
-        p->iov[p->iovs_num].iov_base = pages->block->host + pages->offset[i];
-        p->iov[p->iovs_num].iov_len = p->page_size;
-        p->iovs_num++;
-    }
-
-    p->next_packet_size = pages->num * p->page_size;
+    multifd_send_prepare_iovs(p);
     p->flags |= MULTIFD_FLAG_NOCOMP;
 
     multifd_send_fill_packet(p);
@@ -197,7 +237,7 @@ static void nocomp_recv_cleanup(MultiFDRecvParams *p)
 }
 
 /**
- * nocomp_recv_pages: read the data from the channel into actual pages
+ * nocomp_recv: read the data from the channel
  *
  * For no compression we just need to read things into the correct place.
  *
@@ -206,9 +246,15 @@ static void nocomp_recv_cleanup(MultiFDRecvParams *p)
  * @p: Params for the channel that we are using
  * @errp: pointer to an error
  */
-static int nocomp_recv_pages(MultiFDRecvParams *p, Error **errp)
+static int nocomp_recv(MultiFDRecvParams *p, Error **errp)
 {
-    uint32_t flags = p->flags & MULTIFD_FLAG_COMPRESSION_MASK;
+    uint32_t flags;
+
+    if (!multifd_use_packets()) {
+        return multifd_file_recv_data(p, errp);
+    }
+
+    flags = p->flags & MULTIFD_FLAG_COMPRESSION_MASK;
 
     if (flags != MULTIFD_FLAG_NOCOMP) {
         error_setg(errp, "multifd %u: flags received %x flags expected %x",
@@ -228,7 +274,7 @@ static MultiFDMethods multifd_nocomp_ops = {
     .send_prepare = nocomp_send_prepare,
     .recv_setup = nocomp_recv_setup,
     .recv_cleanup = nocomp_recv_cleanup,
-    .recv_pages = nocomp_recv_pages
+    .recv = nocomp_recv
 };
 
 static MultiFDMethods *multifd_ops[MULTIFD_COMPRESSION__MAX] = {
@@ -663,6 +709,19 @@ static bool multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
 {
     if (p->c) {
         migration_ioc_unregister_yank(p->c);
+        /*
+         * An explicit close() on the channel here is normally not
+         * required, but can be helpful for "file:" iochannels, where it
+         * will include fdatasync() to make sure the data is flushed to the
+         * disk backend.
+         *
+         * The object_unref() cannot guarantee that because: (1) finalize()
+         * of the iochannel is only triggered on the last reference, and
+         * it's not guaranteed that we always hold the last refcount when
+         * reaching here, and, (2) even if finalize() is invoked, it only
+         * does a close(fd) without data flush.
+         */
+        qio_channel_close(p->c, &error_abort);
         object_unref(OBJECT(p->c));
         p->c = NULL;
     }
@@ -684,6 +743,8 @@ static bool multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
 
 static void multifd_send_cleanup_state(void)
 {
+    file_cleanup_outgoing_migration();
+    fd_cleanup_outgoing_migration();
     socket_cleanup_outgoing_migration();
     qemu_sem_destroy(&multifd_send_state->channels_created);
     qemu_sem_destroy(&multifd_send_state->channels_ready);
@@ -795,15 +856,18 @@ static void *multifd_send_thread(void *opaque)
     MigrationThread *thread = NULL;
     Error *local_err = NULL;
     int ret = 0;
+    bool use_packets = multifd_use_packets();
 
     thread = migration_threads_add(p->name, qemu_get_thread_id());
 
     trace_multifd_send_thread_start(p->id);
     rcu_register_thread();
 
-    if (multifd_send_initial_packet(p, &local_err) < 0) {
-        ret = -1;
-        goto out;
+    if (use_packets) {
+        if (multifd_send_initial_packet(p, &local_err) < 0) {
+            ret = -1;
+            goto out;
+        }
     }
 
     while (true) {
@@ -829,8 +893,15 @@ static void *multifd_send_thread(void *opaque)
                 break;
             }
 
-            ret = qio_channel_writev_full_all(p->c, p->iov, p->iovs_num, NULL,
-                                              0, p->write_flags, &local_err);
+            if (migrate_mapped_ram()) {
+                ret = file_write_ramblock_iov(p->c, p->iov, p->iovs_num,
+                                              p->pages->block, &local_err);
+            } else {
+                ret = qio_channel_writev_full_all(p->c, p->iov, p->iovs_num,
+                                                  NULL, 0, p->write_flags,
+                                                  &local_err);
+            }
+
             if (ret != 0) {
                 break;
             }
@@ -854,16 +925,20 @@ static void *multifd_send_thread(void *opaque)
              * it doesn't require explicit memory barriers.
              */
             assert(qatomic_read(&p->pending_sync));
-            p->flags = MULTIFD_FLAG_SYNC;
-            multifd_send_fill_packet(p);
-            ret = qio_channel_write_all(p->c, (void *)p->packet,
-                                        p->packet_len, &local_err);
-            if (ret != 0) {
-                break;
+
+            if (use_packets) {
+                p->flags = MULTIFD_FLAG_SYNC;
+                multifd_send_fill_packet(p);
+                ret = qio_channel_write_all(p->c, (void *)p->packet,
+                                            p->packet_len, &local_err);
+                if (ret != 0) {
+                    break;
+                }
+                /* p->next_packet_size will always be zero for a SYNC packet */
+                stat64_add(&mig_stats.multifd_bytes, p->packet_len);
+                p->flags = 0;
             }
-            /* p->next_packet_size will always be zero for a SYNC packet */
-            stat64_add(&mig_stats.multifd_bytes, p->packet_len);
-            p->flags = 0;
+
             qatomic_set(&p->pending_sync, false);
             qemu_sem_post(&p->sem_sync);
         }
@@ -939,7 +1014,7 @@ static bool multifd_tls_channel_connect(MultiFDSendParams *p,
     return true;
 }
 
-static void multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc)
+void multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc)
 {
     qio_channel_set_delay(ioc, false);
 
@@ -990,7 +1065,7 @@ out:
      * Here we're not interested whether creation succeeded, only that
      * it happened at all.
      */
-    qemu_sem_post(&multifd_send_state->channels_created);
+    multifd_send_channel_created();
 
     if (ret) {
         return;
@@ -1007,9 +1082,14 @@ out:
     error_free(local_err);
 }
 
-static void multifd_new_send_channel_create(gpointer opaque)
+static bool multifd_new_send_channel_create(gpointer opaque, Error **errp)
 {
+    if (!multifd_use_packets()) {
+        return file_send_channel_create(opaque, errp);
+    }
+
     socket_send_channel_create(multifd_new_send_channel_async, opaque);
+    return true;
 }
 
 bool multifd_send_setup(void)
@@ -1018,6 +1098,7 @@ bool multifd_send_setup(void)
     Error *local_err = NULL;
     int thread_count, ret = 0;
     uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
+    bool use_packets = multifd_use_packets();
     uint8_t i;
 
     if (!migrate_multifd()) {
@@ -1040,18 +1121,27 @@ bool multifd_send_setup(void)
         qemu_sem_init(&p->sem_sync, 0);
         p->id = i;
         p->pages = multifd_pages_init(page_count);
-        p->packet_len = sizeof(MultiFDPacket_t)
-                      + sizeof(uint64_t) * page_count;
-        p->packet = g_malloc0(p->packet_len);
-        p->packet->magic = cpu_to_be32(MULTIFD_MAGIC);
-        p->packet->version = cpu_to_be32(MULTIFD_VERSION);
+
+        if (use_packets) {
+            p->packet_len = sizeof(MultiFDPacket_t)
+                          + sizeof(uint64_t) * page_count;
+            p->packet = g_malloc0(p->packet_len);
+            p->packet->magic = cpu_to_be32(MULTIFD_MAGIC);
+            p->packet->version = cpu_to_be32(MULTIFD_VERSION);
+
+            /* We need one extra place for the packet header */
+            p->iov = g_new0(struct iovec, page_count + 1);
+        } else {
+            p->iov = g_new0(struct iovec, page_count);
+        }
         p->name = g_strdup_printf("multifdsend_%d", i);
-        /* We need one extra place for the packet header */
-        p->iov = g_new0(struct iovec, page_count + 1);
         p->page_size = qemu_target_page_size();
         p->page_count = page_count;
         p->write_flags = 0;
-        multifd_new_send_channel_create(p);
+
+        if (!multifd_new_send_channel_create(p, &local_err)) {
+            return false;
+        }
     }
 
     /*
@@ -1083,6 +1173,57 @@ bool multifd_send_setup(void)
     return true;
 }
 
+bool multifd_recv(void)
+{
+    int i;
+    static int next_recv_channel;
+    MultiFDRecvParams *p = NULL;
+    MultiFDRecvData *data = multifd_recv_state->data;
+
+    /*
+     * next_channel can remain from a previous migration that was
+     * using more channels, so ensure it doesn't overflow if the
+     * limit is lower now.
+     */
+    next_recv_channel %= migrate_multifd_channels();
+    for (i = next_recv_channel;; i = (i + 1) % migrate_multifd_channels()) {
+        if (multifd_recv_should_exit()) {
+            return false;
+        }
+
+        p = &multifd_recv_state->params[i];
+
+        if (qatomic_read(&p->pending_job) == false) {
+            next_recv_channel = (i + 1) % migrate_multifd_channels();
+            break;
+        }
+    }
+
+    /*
+     * Order pending_job read before manipulating p->data below. Pairs
+     * with qatomic_store_release() at multifd_recv_thread().
+     */
+    smp_mb_acquire();
+
+    assert(!p->data->size);
+    multifd_recv_state->data = p->data;
+    p->data = data;
+
+    /*
+     * Order p->data update before setting pending_job. Pairs with
+     * qatomic_load_acquire() at multifd_recv_thread().
+     */
+    qatomic_store_release(&p->pending_job, true);
+    qemu_sem_post(&p->sem);
+
+    return true;
+}
+
+MultiFDRecvData *multifd_get_recv_data(void)
+{
+    return multifd_recv_state->data;
+}
+
 static void multifd_recv_terminate_threads(Error *err)
 {
     int i;
@@ -1107,10 +1248,27 @@ static void multifd_recv_terminate_threads(Error *err)
         MultiFDRecvParams *p = &multifd_recv_state->params[i];
 
         /*
-         * multifd_recv_thread may hung at MULTIFD_FLAG_SYNC handle code,
-         * however try to wakeup it without harm in cleanup phase.
+         * The migration thread and channels interact differently
+         * depending on the presence of packets.
          */
-        qemu_sem_post(&p->sem_sync);
+        if (multifd_use_packets()) {
+            /*
+             * The channel receives as long as there are packets. When
+             * packets end (i.e. MULTIFD_FLAG_SYNC is reached), the
+             * channel waits for the migration thread to sync. If the
+             * sync never happens, do it here.
+             */
+            qemu_sem_post(&p->sem_sync);
+        } else {
+            /*
+             * The channel waits for the migration thread to give it
+             * work. When the migration thread runs out of work, it
+             * releases the channel and waits for any pending work to
+             * finish. If we reach here (e.g. due to error) before the
+             * work runs out, release the channel.
+             */
+            qemu_sem_post(&p->sem);
+        }
 
         /*
          * We could arrive here for two reasons:
@@ -1138,6 +1296,7 @@ static void multifd_recv_cleanup_channel(MultiFDRecvParams *p)
     p->c = NULL;
     qemu_mutex_destroy(&p->mutex);
     qemu_sem_destroy(&p->sem_sync);
+    qemu_sem_destroy(&p->sem);
     g_free(p->name);
     p->name = NULL;
     p->packet_len = 0;
@@ -1155,6 +1314,8 @@ static void multifd_recv_cleanup_state(void)
     qemu_sem_destroy(&multifd_recv_state->sem_sync);
     g_free(multifd_recv_state->params);
     multifd_recv_state->params = NULL;
+    g_free(multifd_recv_state->data);
+    multifd_recv_state->data = NULL;
     g_free(multifd_recv_state);
     multifd_recv_state = NULL;
 }
@@ -1182,18 +1343,53 @@ void multifd_recv_cleanup(void)
 
 void multifd_recv_sync_main(void)
 {
+    int thread_count = migrate_multifd_channels();
+    bool file_based = !multifd_use_packets();
     int i;
 
     if (!migrate_multifd()) {
         return;
     }
-    for (i = 0; i < migrate_multifd_channels(); i++) {
-        MultiFDRecvParams *p = &multifd_recv_state->params[i];
 
-        trace_multifd_recv_sync_main_wait(p->id);
+    /*
+     * File-based channels don't use packets and therefore need to
+     * wait for more work. Release them to start the sync.
+     */
+    if (file_based) {
+        for (i = 0; i < thread_count; i++) {
+            MultiFDRecvParams *p = &multifd_recv_state->params[i];
+
+            trace_multifd_recv_sync_main_signal(p->id);
+            qemu_sem_post(&p->sem);
+        }
+    }
+
+    /*
+     * Initiate the synchronization by waiting for all channels.
+     *
+     * For socket-based migration this means each channel has received
+     * the SYNC packet on the stream.
+     *
+     * For file-based migration this means each channel is done with
+     * the work (pending_job=false).
+     */
+    for (i = 0; i < thread_count; i++) {
+        trace_multifd_recv_sync_main_wait(i);
         qemu_sem_wait(&multifd_recv_state->sem_sync);
     }
-    for (i = 0; i < migrate_multifd_channels(); i++) {
+
+    if (file_based) {
+        /*
+         * For file-based loading is done in one iteration. We're
+         * done.
+         */
+        return;
+    }
+
+    /*
+     * Sync done. Release the channels for the next iteration.
+     */
+    for (i = 0; i < thread_count; i++) {
         MultiFDRecvParams *p = &multifd_recv_state->params[i];
 
         WITH_QEMU_LOCK_GUARD(&p->mutex) {
@@ -1211,46 +1407,87 @@ static void *multifd_recv_thread(void *opaque)
 {
     MultiFDRecvParams *p = opaque;
     Error *local_err = NULL;
+    bool use_packets = multifd_use_packets();
     int ret;
 
     trace_multifd_recv_thread_start(p->id);
     rcu_register_thread();
 
     while (true) {
-        uint32_t flags;
+        uint32_t flags = 0;
+        bool has_data = false;
+        p->normal_num = 0;
 
-        if (multifd_recv_should_exit()) {
-            break;
-        }
+        if (use_packets) {
+            if (multifd_recv_should_exit()) {
+                break;
+            }
 
-        ret = qio_channel_read_all_eof(p->c, (void *)p->packet,
-                                       p->packet_len, &local_err);
-        if (ret == 0 || ret == -1) {   /* 0: EOF  -1: Error */
-            break;
-        }
+            ret = qio_channel_read_all_eof(p->c, (void *)p->packet,
+                                           p->packet_len, &local_err);
+            if (ret == 0 || ret == -1) {   /* 0: EOF  -1: Error */
+                break;
+            }
 
-        qemu_mutex_lock(&p->mutex);
-        ret = multifd_recv_unfill_packet(p, &local_err);
-        if (ret) {
+            qemu_mutex_lock(&p->mutex);
+            ret = multifd_recv_unfill_packet(p, &local_err);
+            if (ret) {
+                qemu_mutex_unlock(&p->mutex);
+                break;
+            }
+
+            flags = p->flags;
+            /* recv methods don't know how to handle the SYNC flag */
+            p->flags &= ~MULTIFD_FLAG_SYNC;
+            has_data = !!p->normal_num;
             qemu_mutex_unlock(&p->mutex);
-            break;
-        }
+        } else {
+            /*
+             * No packets, so we need to wait for the vmstate code to
+             * give us work.
+             */
+            qemu_sem_wait(&p->sem);
+
+            if (multifd_recv_should_exit()) {
+                break;
+            }
+
+            /* pairs with qatomic_store_release() at multifd_recv() */
+            if (!qatomic_load_acquire(&p->pending_job)) {
+                /*
+                 * Migration thread did not send work, this is
+                 * equivalent to pending_sync on the sending
+                 * side. Post sem_sync to notify we reached this
+                 * point.
+                 */
+                qemu_sem_post(&multifd_recv_state->sem_sync);
+                continue;
+            }
 
-        flags = p->flags;
-        /* recv methods don't know how to handle the SYNC flag */
-        p->flags &= ~MULTIFD_FLAG_SYNC;
-        qemu_mutex_unlock(&p->mutex);
+            has_data = !!p->data->size;
+        }
 
-        if (p->normal_num) {
-            ret = multifd_recv_state->ops->recv_pages(p, &local_err);
+        if (has_data) {
+            ret = multifd_recv_state->ops->recv(p, &local_err);
             if (ret != 0) {
                 break;
             }
         }
 
-        if (flags & MULTIFD_FLAG_SYNC) {
-            qemu_sem_post(&multifd_recv_state->sem_sync);
-            qemu_sem_wait(&p->sem_sync);
+        if (use_packets) {
+            if (flags & MULTIFD_FLAG_SYNC) {
+                qemu_sem_post(&multifd_recv_state->sem_sync);
+                qemu_sem_wait(&p->sem_sync);
+            }
+        } else {
+            p->total_normal_pages += p->data->size / qemu_target_page_size();
+            p->data->size = 0;
+            /*
+             * Order data->size update before clearing
+             * pending_job. Pairs with smp_mb_acquire() at
+             * multifd_recv().
+             */
+            qatomic_store_release(&p->pending_job, false);
         }
     }
 
@@ -1269,6 +1506,7 @@ int multifd_recv_setup(Error **errp)
 {
     int thread_count;
     uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
+    bool use_packets = multifd_use_packets();
     uint8_t i;
 
     /*
@@ -1282,6 +1520,10 @@ int multifd_recv_setup(Error **errp)
     thread_count = migrate_multifd_channels();
     multifd_recv_state = g_malloc0(sizeof(*multifd_recv_state));
     multifd_recv_state->params = g_new0(MultiFDRecvParams, thread_count);
+
+    multifd_recv_state->data = g_new0(MultiFDRecvData, 1);
+    multifd_recv_state->data->size = 0;
+
     qatomic_set(&multifd_recv_state->count, 0);
     qatomic_set(&multifd_recv_state->exiting, 0);
     qemu_sem_init(&multifd_recv_state->sem_sync, 0);
@@ -1292,10 +1534,18 @@ int multifd_recv_setup(Error **errp)
 
         qemu_mutex_init(&p->mutex);
         qemu_sem_init(&p->sem_sync, 0);
+        qemu_sem_init(&p->sem, 0);
+        p->pending_job = false;
         p->id = i;
-        p->packet_len = sizeof(MultiFDPacket_t)
-                      + sizeof(uint64_t) * page_count;
-        p->packet = g_malloc0(p->packet_len);
+
+        p->data = g_new0(MultiFDRecvData, 1);
+        p->data->size = 0;
+
+        if (use_packets) {
+            p->packet_len = sizeof(MultiFDPacket_t)
+                + sizeof(uint64_t) * page_count;
+            p->packet = g_malloc0(p->packet_len);
+        }
         p->name = g_strdup_printf("multifdrecv_%d", i);
         p->iov = g_new0(struct iovec, page_count);
         p->normal = g_new0(ram_addr_t, page_count);
@@ -1339,18 +1589,23 @@ void multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
 {
     MultiFDRecvParams *p;
     Error *local_err = NULL;
+    bool use_packets = multifd_use_packets();
     int id;
 
-    id = multifd_recv_initial_packet(ioc, &local_err);
-    if (id < 0) {
-        multifd_recv_terminate_threads(local_err);
-        error_propagate_prepend(errp, local_err,
-                                "failed to receive packet"
-                                " via multifd channel %d: ",
-                                qatomic_read(&multifd_recv_state->count));
-        return;
+    if (use_packets) {
+        id = multifd_recv_initial_packet(ioc, &local_err);
+        if (id < 0) {
+            multifd_recv_terminate_threads(local_err);
+            error_propagate_prepend(errp, local_err,
+                                    "failed to receive packet"
+                                    " via multifd channel %d: ",
+                                    qatomic_read(&multifd_recv_state->count));
+            return;
+        }
+        trace_multifd_recv_new_channel(id);
+    } else {
+        id = qatomic_read(&multifd_recv_state->count);
     }
-    trace_multifd_recv_new_channel(id);
 
     p = &multifd_recv_state->params[id];
     if (p->c != NULL) {
diff --git a/migration/multifd.h b/migration/multifd.h
index b3fe27ae93..7447c2bea3 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -13,8 +13,13 @@
 #ifndef QEMU_MIGRATION_MULTIFD_H
 #define QEMU_MIGRATION_MULTIFD_H
 
+#include "ram.h"
+
+typedef struct MultiFDRecvData MultiFDRecvData;
+
 bool multifd_send_setup(void);
 void multifd_send_shutdown(void);
+void multifd_send_channel_created(void);
 int multifd_recv_setup(Error **errp);
 void multifd_recv_cleanup(void);
 void multifd_recv_shutdown(void);
@@ -23,6 +28,8 @@ void multifd_recv_new_channel(QIOChannel *ioc, Error **errp);
 void multifd_recv_sync_main(void);
 int multifd_send_sync_main(void);
 bool multifd_queue_page(RAMBlock *block, ram_addr_t offset);
+bool multifd_recv(void);
+MultiFDRecvData *multifd_get_recv_data(void);
 
 /* Multifd Compression flags */
 #define MULTIFD_FLAG_SYNC (1 << 0)
@@ -63,6 +70,13 @@ typedef struct {
     RAMBlock *block;
 } MultiFDPages_t;
 
+struct MultiFDRecvData {
+    void *opaque;
+    size_t size;
+    /* for preadv */
+    off_t file_offset;
+};
+
 typedef struct {
     /* Fields are only written at creating/deletion time */
     /* No lock required for them, they are read only */
@@ -127,7 +141,7 @@ typedef struct {
     /* number of iovs used */
     uint32_t iovs_num;
     /* used for compression methods */
-    void *data;
+    void *compress_data;
 }  MultiFDSendParams;
 
 typedef struct {
@@ -152,6 +166,8 @@ typedef struct {
 
     /* syncs main thread and channels */
     QemuSemaphore sem_sync;
+    /* sem where to wait for more work */
+    QemuSemaphore sem;
 
     /* this mutex protects the following parameters */
     QemuMutex mutex;
@@ -161,6 +177,8 @@ typedef struct {
     uint32_t flags;
     /* global number of generated multifd packets */
     uint64_t packet_num;
+    int pending_job;
+    MultiFDRecvData *data;
 
     /* thread local variables. No locking required */
 
@@ -183,7 +201,7 @@ typedef struct {
     /* num of non zero pages */
     uint32_t normal_num;
     /* used for de-compression methods */
-    void *data;
+    void *compress_data;
 } MultiFDRecvParams;
 
 typedef struct {
@@ -197,8 +215,8 @@ typedef struct {
     int (*recv_setup)(MultiFDRecvParams *p, Error **errp);
     /* Cleanup for receiving side */
     void (*recv_cleanup)(MultiFDRecvParams *p);
-    /* Read all pages */
-    int (*recv_pages)(MultiFDRecvParams *p, Error **errp);
+    /* Read all data */
+    int (*recv)(MultiFDRecvParams *p, Error **errp);
 } MultiFDMethods;
 
 void multifd_register_ops(int method, MultiFDMethods *ops);
@@ -211,5 +229,6 @@ static inline void multifd_send_prepare_header(MultiFDSendParams *p)
     p->iovs_num++;
 }
 
+void multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc);
 
 #endif
diff --git a/migration/options.c b/migration/options.c
index 3e3e0b93b4..40eb930940 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -204,6 +204,7 @@ Property migration_properties[] = {
     DEFINE_PROP_MIG_CAP("x-switchover-ack",
                         MIGRATION_CAPABILITY_SWITCHOVER_ACK),
     DEFINE_PROP_MIG_CAP("x-dirty-limit", MIGRATION_CAPABILITY_DIRTY_LIMIT),
+    DEFINE_PROP_MIG_CAP("mapped-ram", MIGRATION_CAPABILITY_MAPPED_RAM),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -263,6 +264,13 @@ bool migrate_events(void)
     return s->capabilities[MIGRATION_CAPABILITY_EVENTS];
 }
 
+bool migrate_mapped_ram(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    return s->capabilities[MIGRATION_CAPABILITY_MAPPED_RAM];
+}
+
 bool migrate_ignore_shared(void)
 {
     MigrationState *s = migrate_get_current();
@@ -645,6 +653,26 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
         }
     }
 
+    if (new_caps[MIGRATION_CAPABILITY_MAPPED_RAM]) {
+        if (new_caps[MIGRATION_CAPABILITY_XBZRLE]) {
+            error_setg(errp,
+                       "Mapped-ram migration is incompatible with xbzrle");
+            return false;
+        }
+
+        if (new_caps[MIGRATION_CAPABILITY_COMPRESS]) {
+            error_setg(errp,
+                       "Mapped-ram migration is incompatible with compression");
+            return false;
+        }
+
+        if (new_caps[MIGRATION_CAPABILITY_POSTCOPY_RAM]) {
+            error_setg(errp,
+                       "Mapped-ram migration is incompatible with postcopy");
+            return false;
+        }
+    }
+
     return true;
 }
 
@@ -1218,6 +1246,13 @@ bool migrate_params_check(MigrationParameters *params, Error **errp)
     }
 #endif
 
+    if (migrate_mapped_ram() &&
+        (migrate_multifd_compression() || migrate_tls())) {
+        error_setg(errp,
+                   "Mapped-ram only available for non-compressed non-TLS multifd migration");
+        return false;
+    }
+
     if (params->has_x_vcpu_dirty_limit_period &&
         (params->x_vcpu_dirty_limit_period < 1 ||
          params->x_vcpu_dirty_limit_period > 1000)) {
@@ -1312,6 +1347,12 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
     if (params->has_multifd_compression) {
         dest->multifd_compression = params->multifd_compression;
     }
+    if (params->has_multifd_zlib_level) {
+        dest->multifd_zlib_level = params->multifd_zlib_level;
+    }
+    if (params->has_multifd_zstd_level) {
+        dest->multifd_zstd_level = params->multifd_zstd_level;
+    }
     if (params->has_xbzrle_cache_size) {
         dest->xbzrle_cache_size = params->xbzrle_cache_size;
     }
@@ -1447,6 +1488,12 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
     if (params->has_multifd_compression) {
         s->parameters.multifd_compression = params->multifd_compression;
     }
+    if (params->has_multifd_zlib_level) {
+        s->parameters.multifd_zlib_level = params->multifd_zlib_level;
+    }
+    if (params->has_multifd_zstd_level) {
+        s->parameters.multifd_zstd_level = params->multifd_zstd_level;
+    }
     if (params->has_xbzrle_cache_size) {
         s->parameters.xbzrle_cache_size = params->xbzrle_cache_size;
         xbzrle_cache_resize(params->xbzrle_cache_size, errp);
diff --git a/migration/options.h b/migration/options.h
index 246c160aee..6ddd8dad9b 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -31,6 +31,7 @@ bool migrate_compress(void);
 bool migrate_dirty_bitmaps(void);
 bool migrate_dirty_limit(void);
 bool migrate_events(void);
+bool migrate_mapped_ram(void);
 bool migrate_ignore_shared(void);
 bool migrate_late_block_activate(void);
 bool migrate_multifd(void);
diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 94231ff295..b10c882629 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -33,6 +33,7 @@
 #include "options.h"
 #include "qapi/error.h"
 #include "rdma.h"
+#include "io/channel-file.h"
 
 #define IO_BUF_SIZE 32768
 #define MAX_IOV_SIZE MIN_CONST(IOV_MAX, 64)
@@ -255,6 +256,10 @@ static void qemu_iovec_release_ram(QEMUFile *f)
     memset(f->may_free, 0, sizeof(f->may_free));
 }
 
+bool qemu_file_is_seekable(QEMUFile *f)
+{
+    return qio_channel_has_feature(f->ioc, QIO_CHANNEL_FEATURE_SEEKABLE);
+}
 
 /**
  * Flushes QEMUFile buffer
@@ -447,6 +452,107 @@ void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, size_t size)
     }
 }
 
+void qemu_put_buffer_at(QEMUFile *f, const uint8_t *buf, size_t buflen,
+                        off_t pos)
+{
+    Error *err = NULL;
+    size_t ret;
+
+    if (f->last_error) {
+        return;
+    }
+
+    qemu_fflush(f);
+    ret = qio_channel_pwrite(f->ioc, (char *)buf, buflen, pos, &err);
+
+    if (err) {
+        qemu_file_set_error_obj(f, -EIO, err);
+        return;
+    }
+
+    if ((ssize_t)ret == QIO_CHANNEL_ERR_BLOCK) {
+        qemu_file_set_error_obj(f, -EAGAIN, NULL);
+        return;
+    }
+
+    if (ret != buflen) {
+        error_setg(&err, "Partial write of size %zu, expected %zu", ret,
+                   buflen);
+        qemu_file_set_error_obj(f, -EIO, err);
+        return;
+    }
+
+    stat64_add(&mig_stats.qemu_file_transferred, buflen);
+
+    return;
+}
+
+
+size_t qemu_get_buffer_at(QEMUFile *f, const uint8_t *buf, size_t buflen,
+                          off_t pos)
+{
+    Error *err = NULL;
+    size_t ret;
+
+    if (f->last_error) {
+        return 0;
+    }
+
+    ret = qio_channel_pread(f->ioc, (char *)buf, buflen, pos, &err);
+
+    if ((ssize_t)ret == -1 || err) {
+        qemu_file_set_error_obj(f, -EIO, err);
+        return 0;
+    }
+
+    if ((ssize_t)ret == QIO_CHANNEL_ERR_BLOCK) {
+        qemu_file_set_error_obj(f, -EAGAIN, NULL);
+        return 0;
+    }
+
+    if (ret != buflen) {
+        error_setg(&err, "Partial read of size %zu, expected %zu", ret, buflen);
+        qemu_file_set_error_obj(f, -EIO, err);
+        return 0;
+    }
+
+    return ret;
+}
+
+void qemu_set_offset(QEMUFile *f, off_t off, int whence)
+{
+    Error *err = NULL;
+    off_t ret;
+
+    if (qemu_file_is_writable(f)) {
+        qemu_fflush(f);
+    } else {
+        /* Drop all cached buffers if existed; will trigger a re-fill later */
+        f->buf_index = 0;
+        f->buf_size = 0;
+    }
+
+    ret = qio_channel_io_seek(f->ioc, off, whence, &err);
+    if (ret == (off_t)-1) {
+        qemu_file_set_error_obj(f, -EIO, err);
+    }
+}
+
+off_t qemu_get_offset(QEMUFile *f)
+{
+    Error *err = NULL;
+    off_t ret;
+
+    qemu_fflush(f);
+
+    ret = qio_channel_io_seek(f->ioc, 0, SEEK_CUR, &err);
+    if (ret == (off_t)-1) {
+        qemu_file_set_error_obj(f, -EIO, err);
+    }
+    return ret;
+}
+
+
 void qemu_put_byte(QEMUFile *f, int v)
 {
     if (f->last_error) {
diff --git a/migration/qemu-file.h b/migration/qemu-file.h
index 8aec9fabf7..32fd4a34fd 100644
--- a/migration/qemu-file.h
+++ b/migration/qemu-file.h
@@ -75,6 +75,12 @@ QEMUFile *qemu_file_get_return_path(QEMUFile *f);
 int qemu_fflush(QEMUFile *f);
 void qemu_file_set_blocking(QEMUFile *f, bool block);
 int qemu_file_get_to_fd(QEMUFile *f, int fd, size_t size);
+void qemu_set_offset(QEMUFile *f, off_t off, int whence);
+off_t qemu_get_offset(QEMUFile *f);
+void qemu_put_buffer_at(QEMUFile *f, const uint8_t *buf, size_t buflen,
+                        off_t pos);
+size_t qemu_get_buffer_at(QEMUFile *f, const uint8_t *buf, size_t buflen,
+                          off_t pos);
 
 QIOChannel *qemu_file_get_ioc(QEMUFile *file);
 
diff --git a/migration/ram.c b/migration/ram.c
index 83fd780fc2..003c28e133 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -94,6 +94,24 @@
 #define RAM_SAVE_FLAG_MULTIFD_FLUSH    0x200
 /* We can't use any flag that is bigger than 0x200 */
 
+/*
+ * mapped-ram migration supports O_DIRECT, so we need to make sure the
+ * userspace buffer, the IO operation size and the file offset are
+ * aligned according to the underlying device's block size. The first
+ * two are already aligned to page size, but we need to add padding to
+ * the file to align the offset.  We cannot read the block size
+ * dynamically because the migration file can be moved between
+ * different systems, so use 1M to cover most block sizes and to keep
+ * the file offset aligned at page size as well.
+ */
+#define MAPPED_RAM_FILE_OFFSET_ALIGNMENT 0x100000
+
+/*
+ * When doing mapped-ram migration, this is the amount we read from
+ * the pages region in the migration file at a time.
+ */
+#define MAPPED_RAM_LOAD_BUF_SIZE 0x100000
+
 XBZRLECacheStats xbzrle_counters;
 
 /* used by the search for pages to send */
@@ -1126,12 +1144,18 @@ static int save_zero_page(RAMState *rs, PageSearchStatus *pss,
         return 0;
     }
 
+    stat64_add(&mig_stats.zero_pages, 1);
+
+    if (migrate_mapped_ram()) {
+        /* zero pages are not transferred with mapped-ram */
+        clear_bit_atomic(offset >> TARGET_PAGE_BITS, pss->block->file_bmap);
+        return 1;
+    }
+
     len += save_page_header(pss, file, pss->block, offset | RAM_SAVE_FLAG_ZERO);
     qemu_put_byte(file, 0);
     len += 1;
     ram_release_page(pss->block->idstr, offset);
-
-    stat64_add(&mig_stats.zero_pages, 1);
     ram_transferred_add(len);
 
     /*
@@ -1189,14 +1213,20 @@ static int save_normal_page(PageSearchStatus *pss, RAMBlock *block,
 {
     QEMUFile *file = pss->pss_channel;
 
-    ram_transferred_add(save_page_header(pss, pss->pss_channel, block,
-                                         offset | RAM_SAVE_FLAG_PAGE));
-    if (async) {
-        qemu_put_buffer_async(file, buf, TARGET_PAGE_SIZE,
-                              migrate_release_ram() &&
-                              migration_in_postcopy());
+    if (migrate_mapped_ram()) {
+        qemu_put_buffer_at(file, buf, TARGET_PAGE_SIZE,
+                           block->pages_offset + offset);
+        set_bit(offset >> TARGET_PAGE_BITS, block->file_bmap);
     } else {
-        qemu_put_buffer(file, buf, TARGET_PAGE_SIZE);
+        ram_transferred_add(save_page_header(pss, pss->pss_channel, block,
+                                             offset | RAM_SAVE_FLAG_PAGE));
+        if (async) {
+            qemu_put_buffer_async(file, buf, TARGET_PAGE_SIZE,
+                                  migrate_release_ram() &&
+                                  migration_in_postcopy());
+        } else {
+            qemu_put_buffer(file, buf, TARGET_PAGE_SIZE);
+        }
     }
     ram_transferred_add(TARGET_PAGE_SIZE);
     stat64_add(&mig_stats.normal_pages, 1);
@@ -1332,14 +1362,18 @@ static int find_dirty_block(RAMState *rs, PageSearchStatus *pss)
         pss->block = QLIST_NEXT_RCU(pss->block, next);
         if (!pss->block) {
             if (migrate_multifd() &&
-                !migrate_multifd_flush_after_each_section()) {
+                (!migrate_multifd_flush_after_each_section() ||
+                 migrate_mapped_ram())) {
                 QEMUFile *f = rs->pss[RAM_CHANNEL_PRECOPY].pss_channel;
                 int ret = multifd_send_sync_main();
                 if (ret < 0) {
                     return ret;
                 }
-                qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
-                qemu_fflush(f);
+
+                if (!migrate_mapped_ram()) {
+                    qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
+                    qemu_fflush(f);
+                }
             }
             /*
              * If memory migration starts over, we will meet a dirtied page
@@ -2778,6 +2812,9 @@ static void ram_list_init_bitmaps(void)
              */
             block->bmap = bitmap_new(pages);
             bitmap_set(block->bmap, 0, pages);
+            if (migrate_mapped_ram()) {
+                block->file_bmap = bitmap_new(pages);
+            }
             block->clear_bmap_shift = shift;
             block->clear_bmap = bitmap_new(clear_bmap_size(pages, shift));
         }
@@ -2915,6 +2952,89 @@ void qemu_guest_free_page_hint(void *addr, size_t len)
     }
 }
 
+#define MAPPED_RAM_HDR_VERSION 1
+struct MappedRamHeader {
+    uint32_t version;
+    /*
+     * The target's page size, so we know how many pages are in the
+     * bitmap.
+     */
+    uint64_t page_size;
+    /*
+     * The offset in the migration file where the pages bitmap is
+     * stored.
+     */
+    uint64_t bitmap_offset;
+    /*
+     * The offset in the migration file where the actual pages (data)
+     * are stored.
+     */
+    uint64_t pages_offset;
+} QEMU_PACKED;
+typedef struct MappedRamHeader MappedRamHeader;
+
+static void mapped_ram_setup_ramblock(QEMUFile *file, RAMBlock *block)
+{
+    g_autofree MappedRamHeader *header = NULL;
+    size_t header_size, bitmap_size;
+    long num_pages;
+
+    header = g_new0(MappedRamHeader, 1);
+    header_size = sizeof(MappedRamHeader);
+
+    num_pages = block->used_length >> TARGET_PAGE_BITS;
+    bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long);
+
+    /*
+     * Save the file offsets of where the bitmap and the pages should
+     * go as they are written at the end of migration and during the
+     * iterative phase, respectively.
+     */
+    block->bitmap_offset = qemu_get_offset(file) + header_size;
+    block->pages_offset = ROUND_UP(block->bitmap_offset +
+                                   bitmap_size,
+                                   MAPPED_RAM_FILE_OFFSET_ALIGNMENT);
+
+    header->version = cpu_to_be32(MAPPED_RAM_HDR_VERSION);
+    header->page_size = cpu_to_be64(TARGET_PAGE_SIZE);
+    header->bitmap_offset = cpu_to_be64(block->bitmap_offset);
+    header->pages_offset = cpu_to_be64(block->pages_offset);
+
+    qemu_put_buffer(file, (uint8_t *) header, header_size);
+
+    /* prepare offset for next ramblock */
+    qemu_set_offset(file, block->pages_offset + block->used_length, SEEK_SET);
+}
+
+static bool mapped_ram_read_header(QEMUFile *file, MappedRamHeader *header,
+                                   Error **errp)
+{
+    size_t ret, header_size = sizeof(MappedRamHeader);
+
+    ret = qemu_get_buffer(file, (uint8_t *)header, header_size);
+    if (ret != header_size) {
+        error_setg(errp, "Could not read whole mapped-ram migration header "
+                   "(expected %zd, got %zd bytes)", header_size, ret);
+        return false;
+    }
+
+    /* migration stream is big-endian */
+    header->version = be32_to_cpu(header->version);
+
+    if (header->version > MAPPED_RAM_HDR_VERSION) {
+        error_setg(errp, "Migration mapped-ram capability version not "
+                   "supported (expected <= %d, got %d)", MAPPED_RAM_HDR_VERSION,
+                   header->version);
+        return false;
+    }
+
+    header->page_size = be64_to_cpu(header->page_size);
+    header->bitmap_offset = be64_to_cpu(header->bitmap_offset);
+    header->pages_offset = be64_to_cpu(header->pages_offset);
+
+    return true;
+}
+
 /*
  * Each of ram_save_setup, ram_save_iterate and ram_save_complete has
  * long-running RCU critical section.  When rcu-reclaims in the code
@@ -2970,6 +3090,10 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
             if (migrate_ignore_shared()) {
                 qemu_put_be64(f, block->mr->addr);
             }
+
+            if (migrate_mapped_ram()) {
+                mapped_ram_setup_ramblock(f, block);
+            }
         }
     }
 
@@ -2995,7 +3119,8 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
         return ret;
     }
 
-    if (migrate_multifd() && !migrate_multifd_flush_after_each_section()) {
+    if (migrate_multifd() && !migrate_multifd_flush_after_each_section()
+        && !migrate_mapped_ram()) {
         qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
     }
 
@@ -3003,6 +3128,33 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     return qemu_fflush(f);
 }
 
+static void ram_save_file_bmap(QEMUFile *f)
+{
+    RAMBlock *block;
+
+    RAMBLOCK_FOREACH_MIGRATABLE(block) {
+        long num_pages = block->used_length >> TARGET_PAGE_BITS;
+        long bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long);
+
+        qemu_put_buffer_at(f, (uint8_t *)block->file_bmap, bitmap_size,
+                           block->bitmap_offset);
+        ram_transferred_add(bitmap_size);
+
+        /*
+         * Free the bitmap here to catch any synchronization issues
+         * with multifd channels. No channels should be sending pages
+         * after we've written the bitmap to file.
+         */
+        g_free(block->file_bmap);
+        block->file_bmap = NULL;
+    }
+}
+
+void ramblock_set_file_bmap_atomic(RAMBlock *block, ram_addr_t offset)
+{
+    set_bit_atomic(offset >> TARGET_PAGE_BITS, block->file_bmap);
+}
+
 /**
  * ram_save_iterate: iterative stage for migration
  *
@@ -3112,7 +3264,8 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
 out:
     if (ret >= 0
         && migration_is_setup_or_active(migrate_get_current()->state)) {
-        if (migrate_multifd() && migrate_multifd_flush_after_each_section()) {
+        if (migrate_multifd() && migrate_multifd_flush_after_each_section() &&
+            !migrate_mapped_ram()) {
             ret = multifd_send_sync_main();
             if (ret < 0) {
                 return ret;
@@ -3192,7 +3345,20 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
         return ret;
     }
 
-    if (migrate_multifd() && !migrate_multifd_flush_after_each_section()) {
+    if (migrate_mapped_ram()) {
+        ram_save_file_bmap(f);
+
+        if (qemu_file_get_error(f)) {
+            Error *local_err = NULL;
+            int err = qemu_file_get_error_obj(f, &local_err);
+
+            error_reportf_err(local_err, "Failed to write bitmap to file: ");
+            return -err;
+        }
+    }
+
+    if (migrate_multifd() && !migrate_multifd_flush_after_each_section() &&
+        !migrate_mapped_ram()) {
         qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
     }
     qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
@@ -3792,23 +3958,149 @@ void colo_flush_ram_cache(void)
     trace_colo_flush_ram_cache_end();
 }
 
+static size_t ram_load_multifd_pages(void *host_addr, size_t size,
+                                     uint64_t offset)
+{
+    MultiFDRecvData *data = multifd_get_recv_data();
+
+    data->opaque = host_addr;
+    data->file_offset = offset;
+    data->size = size;
+
+    if (!multifd_recv()) {
+        return 0;
+    }
+
+    return size;
+}
+
+static bool read_ramblock_mapped_ram(QEMUFile *f, RAMBlock *block,
+                                     long num_pages, unsigned long *bitmap,
+                                     Error **errp)
+{
+    ERRP_GUARD();
+    unsigned long set_bit_idx, clear_bit_idx;
+    ram_addr_t offset;
+    void *host;
+    size_t read, unread, size;
+
+    for (set_bit_idx = find_first_bit(bitmap, num_pages);
+         set_bit_idx < num_pages;
+         set_bit_idx = find_next_bit(bitmap, num_pages, clear_bit_idx + 1)) {
+
+        clear_bit_idx = find_next_zero_bit(bitmap, num_pages, set_bit_idx + 1);
+
+        unread = TARGET_PAGE_SIZE * (clear_bit_idx - set_bit_idx);
+        offset = set_bit_idx << TARGET_PAGE_BITS;
+
+        while (unread > 0) {
+            host = host_from_ram_block_offset(block, offset);
+            if (!host) {
+                error_setg(errp, "page outside of ramblock %s range",
+                           block->idstr);
+                return false;
+            }
+
+            size = MIN(unread, MAPPED_RAM_LOAD_BUF_SIZE);
+
+            if (migrate_multifd()) {
+                read = ram_load_multifd_pages(host, size,
+                                              block->pages_offset + offset);
+            } else {
+                read = qemu_get_buffer_at(f, host, size,
+                                          block->pages_offset + offset);
+            }
+
+            if (!read) {
+                goto err;
+            }
+            offset += read;
+            unread -= read;
+        }
+    }
+
+    return true;
+
+err:
+    qemu_file_get_error_obj(f, errp);
+    error_prepend(errp, "(%s) failed to read page " RAM_ADDR_FMT
+                  "from file offset %" PRIx64 ": ", block->idstr, offset,
+                  block->pages_offset + offset);
+    return false;
+}
+
+static void parse_ramblock_mapped_ram(QEMUFile *f, RAMBlock *block,
+                                      ram_addr_t length, Error **errp)
+{
+    g_autofree unsigned long *bitmap = NULL;
+    MappedRamHeader header;
+    size_t bitmap_size;
+    long num_pages;
+
+    if (!mapped_ram_read_header(f, &header, errp)) {
+        return;
+    }
+
+    block->pages_offset = header.pages_offset;
+
+    /*
+     * Check the alignment of the file region that contains pages. We
+     * don't enforce MAPPED_RAM_FILE_OFFSET_ALIGNMENT to allow that
+     * value to change in the future. Do only a sanity check with page
+     * size alignment.
+     */
+    if (!QEMU_IS_ALIGNED(block->pages_offset, TARGET_PAGE_SIZE)) {
+        error_setg(errp,
+                   "Error reading ramblock %s pages, region has bad alignment",
+                   block->idstr);
+        return;
+    }
+
+    num_pages = length / header.page_size;
+    bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long);
+
+    bitmap = g_malloc0(bitmap_size);
+    if (qemu_get_buffer_at(f, (uint8_t *)bitmap, bitmap_size,
+                           header.bitmap_offset) != bitmap_size) {
+        error_setg(errp, "Error reading dirty bitmap");
+        return;
+    }
+
+    if (!read_ramblock_mapped_ram(f, block, num_pages, bitmap, errp)) {
+        return;
+    }
+
+    /* Skip pages array */
+    qemu_set_offset(f, block->pages_offset + length, SEEK_SET);
+
+    return;
+}
+
 static int parse_ramblock(QEMUFile *f, RAMBlock *block, ram_addr_t length)
 {
     int ret = 0;
     /* ADVISE is earlier, it shows the source has the postcopy capability on */
     bool postcopy_advised = migration_incoming_postcopy_advised();
     int max_hg_page_size;
+    Error *local_err = NULL;
 
     assert(block);
 
+    if (migrate_mapped_ram()) {
+        parse_ramblock_mapped_ram(f, block, length, &local_err);
+        if (local_err) {
+            error_report_err(local_err);
+            return -EINVAL;
+        }
+        return 0;
+    }
+
     if (!qemu_ram_is_migratable(block)) {
         error_report("block %s should not be migrated !", block->idstr);
         return -EINVAL;
     }
 
     if (length != block->used_length) {
-        Error *local_err = NULL;
-
         ret = qemu_ram_resize(block, length, &local_err);
         if (local_err) {
             error_report_err(local_err);
@@ -3899,6 +4191,12 @@ static int ram_load_precopy(QEMUFile *f)
         invalid_flags |= RAM_SAVE_FLAG_COMPRESS_PAGE;
     }
 
+    if (migrate_mapped_ram()) {
+        invalid_flags |= (RAM_SAVE_FLAG_HOOK | RAM_SAVE_FLAG_MULTIFD_FLUSH |
+                          RAM_SAVE_FLAG_PAGE | RAM_SAVE_FLAG_XBZRLE |
+                          RAM_SAVE_FLAG_ZERO);
+    }
+
     while (!ret && !(flags & RAM_SAVE_FLAG_EOS)) {
         ram_addr_t addr;
         void *host = NULL, *host_bak = NULL;
@@ -3920,6 +4218,8 @@ static int ram_load_precopy(QEMUFile *f)
         addr &= TARGET_PAGE_MASK;
 
         if (flags & invalid_flags) {
+            error_report("Unexpected RAM flags: %d", flags & invalid_flags);
+
             if (flags & invalid_flags & RAM_SAVE_FLAG_COMPRESS_PAGE) {
                 error_report("Received an unexpected compressed page");
             }
@@ -3972,6 +4272,16 @@ static int ram_load_precopy(QEMUFile *f)
         switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
         case RAM_SAVE_FLAG_MEM_SIZE:
             ret = parse_ramblocks(f, addr);
+            /*
+             * For mapped-ram migration (to a file) using multifd, we sync
+             * once and for all here to make sure all tasks we queued to
+             * multifd threads are completed, so that all the ramblocks
+             * (including all the guest memory pages within) are fully
+             * loaded after this sync returns.
+             */
+            if (migrate_mapped_ram()) {
+                multifd_recv_sync_main();
+            }
             break;
 
         case RAM_SAVE_FLAG_ZERO:
@@ -4012,7 +4322,12 @@ static int ram_load_precopy(QEMUFile *f)
         case RAM_SAVE_FLAG_EOS:
             /* normal exit */
             if (migrate_multifd() &&
-                migrate_multifd_flush_after_each_section()) {
+                migrate_multifd_flush_after_each_section() &&
+                /*
+                 * Mapped-ram migration flushes once and for all after
+                 * parsing ramblocks. Always ignore EOS for it.
+                 */
+                !migrate_mapped_ram()) {
                 multifd_recv_sync_main();
             }
             break;
diff --git a/migration/ram.h b/migration/ram.h
index 9b937a446b..b9ac0da587 100644
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -75,6 +75,7 @@ bool ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *rb, Error **errp);
 bool ramblock_page_is_discarded(RAMBlock *rb, ram_addr_t start);
 void postcopy_preempt_shutdown_file(MigrationState *s);
 void *postcopy_preempt_thread(void *opaque);
+void ramblock_set_file_bmap_atomic(RAMBlock *block, ram_addr_t offset);
 
 /* ram cache */
 int colo_init_ram_cache(void);
diff --git a/migration/savevm.c b/migration/savevm.c
index d612c8a902..dc1fb9c0d3 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -245,6 +245,7 @@ static bool should_validate_capability(int capability)
     /* Validate only new capabilities to keep compatibility. */
     switch (capability) {
     case MIGRATION_CAPABILITY_X_IGNORE_SHARED:
+    case MIGRATION_CAPABILITY_MAPPED_RAM:
         return true;
     default:
         return false;
diff --git a/migration/trace-events b/migration/trace-events
index 298ad2b0dd..bf1a069632 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -132,7 +132,7 @@ multifd_recv(uint8_t id, uint64_t packet_num, uint32_t used, uint32_t flags, uin
 multifd_recv_new_channel(uint8_t id) "channel %u"
 multifd_recv_sync_main(long packet_num) "packet num %ld"
 multifd_recv_sync_main_signal(uint8_t id) "channel %u"
-multifd_recv_sync_main_wait(uint8_t id) "channel %u"
+multifd_recv_sync_main_wait(uint8_t id) "iter %u"
 multifd_recv_terminate_threads(bool error) "error %d"
 multifd_recv_thread_end(uint8_t id, uint64_t packets, uint64_t pages) "channel %u packets %" PRIu64 " pages %" PRIu64
 multifd_recv_thread_start(uint8_t id) "%u"
diff --git a/qapi/migration.json b/qapi/migration.json
index 0b33a71ab4..62acc834af 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -531,6 +531,10 @@
 #     and can result in more stable read performance.  Requires KVM
 #     with accelerator property "dirty-ring-size" set.  (Since 8.1)
 #
+# @mapped-ram: Migrate using fixed offsets in the migration file for
+#     each RAM page.  Requires a migration URI that supports seeking,
+#     such as a file.  (since 9.0)
+#
 # Features:
 #
 # @deprecated: Member @block is deprecated.  Use blockdev-mirror with
@@ -555,7 +559,7 @@
            { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
            'validate-uuid', 'background-snapshot',
            'zero-copy-send', 'postcopy-preempt', 'switchover-ack',
-           'dirty-limit'] }
+           'dirty-limit', 'mapped-ram'] }
 
 ##
 # @MigrationCapabilityStatus:
@@ -636,28 +640,30 @@
 #
 # @normal: the original form of migration. (since 8.2)
 #
-# @cpr-reboot: The migrate command stops the VM and saves state to the URI.
-#     After quitting qemu, the user resumes by running qemu -incoming.
+# @cpr-reboot: The migrate command stops the VM and saves state to
+#     the URI.  After quitting QEMU, the user resumes by running
+#     QEMU -incoming.
 #
-#     This mode allows the user to quit qemu, and restart an updated version
-#     of qemu.  The user may even update and reboot the OS before restarting,
-#     as long as the URI persists across a reboot.
+#     This mode allows the user to quit QEMU, optionally update and
+#     reboot the OS, and restart QEMU.  If the user reboots, the URI
+#     must persist across the reboot, such as by using a file.
 #
-#     Unlike normal mode, the use of certain local storage options does not
-#     block the migration, but the user must not modify guest block devices
-#     between the quit and restart.
+#     Unlike normal mode, the use of certain local storage options
+#     does not block the migration, but the user must not modify the
+#     contents of guest block devices between the quit and restart.
 #
-#     This mode supports vfio devices provided the user first puts the guest
-#     in the suspended runstate, such as by issuing guest-suspend-ram to the
-#     qemu guest agent.
+#     This mode supports VFIO devices provided the user first puts
+#     the guest in the suspended runstate, such as by issuing
+#     guest-suspend-ram to the QEMU guest agent.
 #
-#     Best performance is achieved when the memory backend is shared and the
-#     @x-ignore-shared migration capability is set, but this is not required.
-#     Further, if the user reboots before restarting such a configuration, the
-#     shared backend must be be non-volatile across reboot, such as by backing
-#     it with a dax device.
+#     Best performance is achieved when the memory backend is shared
+#     and the @x-ignore-shared migration capability is set, but this
+#     is not required.  Further, if the user reboots before restarting
+#     such a configuration, the shared memory must persist across the
+#     reboot, such as by backing it with a dax device.
 #
-#     cpr-reboot may not be used with postcopy, colo, or background-snapshot.
+#     @cpr-reboot may not be used with postcopy, background-snapshot,
+#     or COLO.
 #
 #     (since 8.2)
 ##
diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
index 83512bce85..4023d808f9 100644
--- a/tests/qtest/migration-test.c
+++ b/tests/qtest/migration-test.c
@@ -2200,6 +2200,14 @@ static void *test_mode_reboot_start(QTestState *from, QTestState *to)
     return NULL;
 }
 
+static void *migrate_mapped_ram_start(QTestState *from, QTestState *to)
+{
+    migrate_set_capability(from, "mapped-ram", true);
+    migrate_set_capability(to, "mapped-ram", true);
+
+    return NULL;
+}
+
 static void test_mode_reboot(void)
 {
     g_autofree char *uri = g_strdup_printf("file:%s/%s", tmpfs,
@@ -2214,6 +2222,72 @@ static void test_mode_reboot(void)
     test_file_common(&args, true);
 }
 
+static void test_precopy_file_mapped_ram_live(void)
+{
+    g_autofree char *uri = g_strdup_printf("file:%s/%s", tmpfs,
+                                           FILE_TEST_FILENAME);
+    MigrateCommon args = {
+        .connect_uri = uri,
+        .listen_uri = "defer",
+        .start_hook = migrate_mapped_ram_start,
+    };
+
+    test_file_common(&args, false);
+}
+
+static void test_precopy_file_mapped_ram(void)
+{
+    g_autofree char *uri = g_strdup_printf("file:%s/%s", tmpfs,
+                                           FILE_TEST_FILENAME);
+    MigrateCommon args = {
+        .connect_uri = uri,
+        .listen_uri = "defer",
+        .start_hook = migrate_mapped_ram_start,
+    };
+
+    test_file_common(&args, true);
+}
+
+static void *migrate_multifd_mapped_ram_start(QTestState *from, QTestState *to)
+{
+    migrate_mapped_ram_start(from, to);
+
+    migrate_set_parameter_int(from, "multifd-channels", 4);
+    migrate_set_parameter_int(to, "multifd-channels", 4);
+
+    migrate_set_capability(from, "multifd", true);
+    migrate_set_capability(to, "multifd", true);
+
+    return NULL;
+}
+
+static void test_multifd_file_mapped_ram_live(void)
+{
+    g_autofree char *uri = g_strdup_printf("file:%s/%s", tmpfs,
+                                           FILE_TEST_FILENAME);
+    MigrateCommon args = {
+        .connect_uri = uri,
+        .listen_uri = "defer",
+        .start_hook = migrate_multifd_mapped_ram_start,
+    };
+
+    test_file_common(&args, false);
+}
+
+static void test_multifd_file_mapped_ram(void)
+{
+    g_autofree char *uri = g_strdup_printf("file:%s/%s", tmpfs,
+                                           FILE_TEST_FILENAME);
+    MigrateCommon args = {
+        .connect_uri = uri,
+        .listen_uri = "defer",
+        .start_hook = migrate_multifd_mapped_ram_start,
+    };
+
+    test_file_common(&args, true);
+}
+
+
 static void test_precopy_tcp_plain(void)
 {
     MigrateCommon args = {
@@ -2462,6 +2536,13 @@ static void *migrate_precopy_fd_file_start(QTestState *from, QTestState *to)
     return NULL;
 }
 
+static void *migrate_fd_file_mapped_ram_start(QTestState *from, QTestState *to)
+{
+    migrate_mapped_ram_start(from, to);
+
+    return migrate_precopy_fd_file_start(from, to);
+}
+
 static void test_migrate_precopy_fd_file(void)
 {
     MigrateCommon args = {
@@ -2472,6 +2553,36 @@ static void test_migrate_precopy_fd_file(void)
     };
     test_file_common(&args, true);
 }
+
+static void test_migrate_precopy_fd_file_mapped_ram(void)
+{
+    MigrateCommon args = {
+        .listen_uri = "defer",
+        .connect_uri = "fd:fd-mig",
+        .start_hook = migrate_fd_file_mapped_ram_start,
+        .finish_hook = test_migrate_fd_finish_hook
+    };
+    test_file_common(&args, true);
+}
+
+static void *migrate_multifd_fd_mapped_ram_start(QTestState *from,
+                                                QTestState *to)
+{
+    migrate_multifd_mapped_ram_start(from, to);
+    return migrate_precopy_fd_file_start(from, to);
+}
+
+static void test_multifd_fd_mapped_ram(void)
+{
+    MigrateCommon args = {
+        .connect_uri = "fd:fd-mig",
+        .listen_uri = "defer",
+        .start_hook = migrate_multifd_fd_mapped_ram_start,
+        .finish_hook = test_migrate_fd_finish_hook
+    };
+
+    test_file_common(&args, true);
+}
 #endif /* _WIN32 */
 
 static void do_test_validate_uuid(MigrateStart *args, bool should_fail)
@@ -2664,6 +2775,13 @@ static void *
 test_migrate_precopy_tcp_multifd_zlib_start(QTestState *from,
                                             QTestState *to)
 {
+    /*
+     * Overloading this test to also check that set_parameter does not error.
+     * This is also done in the tests for the other compression methods.
+     */
+    migrate_set_parameter_int(from, "multifd-zlib-level", 2);
+    migrate_set_parameter_int(to, "multifd-zlib-level", 2);
+
     return test_migrate_precopy_tcp_multifd_start_common(from, to, "zlib");
 }
 
@@ -2672,6 +2790,9 @@ static void *
 test_migrate_precopy_tcp_multifd_zstd_start(QTestState *from,
                                             QTestState *to)
 {
+    migrate_set_parameter_int(from, "multifd-zstd-level", 2);
+    migrate_set_parameter_int(to, "multifd-zstd-level", 2);
+
     return test_migrate_precopy_tcp_multifd_start_common(from, to, "zstd");
 }
 #endif /* CONFIG_ZSTD */
@@ -3509,6 +3630,20 @@ int main(int argc, char **argv)
         migration_test_add("/migration/mode/reboot", test_mode_reboot);
     }
 
+    migration_test_add("/migration/precopy/file/mapped-ram",
+                       test_precopy_file_mapped_ram);
+    migration_test_add("/migration/precopy/file/mapped-ram/live",
+                       test_precopy_file_mapped_ram_live);
+
+    migration_test_add("/migration/multifd/file/mapped-ram",
+                       test_multifd_file_mapped_ram);
+    migration_test_add("/migration/multifd/file/mapped-ram/live",
+                       test_multifd_file_mapped_ram_live);
+#ifndef _WIN32
+    migration_test_add("/migration/multifd/fd/mapped-ram",
+                       test_multifd_fd_mapped_ram);
+#endif
+
 #ifdef CONFIG_GNUTLS
     migration_test_add("/migration/precopy/unix/tls/psk",
                        test_precopy_unix_tls_psk);
@@ -3570,6 +3705,8 @@ int main(int argc, char **argv)
                        test_migrate_precopy_fd_socket);
     migration_test_add("/migration/precopy/fd/file",
                        test_migrate_precopy_fd_file);
+    migration_test_add("/migration/precopy/fd/file/mapped-ram",
+                       test_migrate_precopy_fd_file_mapped_ram);
 #endif
     migration_test_add("/migration/validate_uuid", test_validate_uuid);
     migration_test_add("/migration/validate_uuid_error",