Merge tag 'mem-2024-02-06-v3' of https://github.com/davidhildenbrand/qemu into staging

Hi,

"Host Memory Backends" and "Memory devices" queue ("mem"):
- Reintroduce memory region size checks for memory devices; the removal
  lead to some undesired side effects
- Preallocate memory of memory backends in selected configurations
  asynchronously (so we preallocate concurrently), to speed up QEMU
  startup time.

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* tag 'mem-2024-02-06-v3' of https://github.com/davidhildenbrand/qemu:
  oslib-posix: initialize backend memory objects in parallel
  memory-device: reintroduce memory region size check
  hv-balloon: use get_min_alignment() to express 32 GiB alignment

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

1 files changed, 100 insertions, 31 deletions

diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 7c297003b9..3c379f96c2 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -42,6 +42,7 @@
 #include "qemu/cutils.h"
 #include "qemu/units.h"
 #include "qemu/thread-context.h"
+#include "qemu/main-loop.h"
 
 #ifdef CONFIG_LINUX
 #include <sys/syscall.h>
@@ -63,11 +64,15 @@
 
 struct MemsetThread;
 
+static QLIST_HEAD(, MemsetContext) memset_contexts =
+    QLIST_HEAD_INITIALIZER(memset_contexts);
+
 typedef struct MemsetContext {
     bool all_threads_created;
     bool any_thread_failed;
     struct MemsetThread *threads;
     int num_threads;
+    QLIST_ENTRY(MemsetContext) next;
 } MemsetContext;
 
 struct MemsetThread {
@@ -412,19 +417,44 @@ static inline int get_memset_num_threads(size_t hpagesize, size_t numpages,
     return ret;
 }
 
+static int wait_and_free_mem_prealloc_context(MemsetContext *context)
+{
+    int i, ret = 0, tmp;
+
+    for (i = 0; i < context->num_threads; i++) {
+        tmp = (uintptr_t)qemu_thread_join(&context->threads[i].pgthread);
+
+        if (tmp) {
+            ret = tmp;
+        }
+    }
+    g_free(context->threads);
+    g_free(context);
+    return ret;
+}
+
 static int touch_all_pages(char *area, size_t hpagesize, size_t numpages,
-                           int max_threads, ThreadContext *tc,
+                           int max_threads, ThreadContext *tc, bool async,
                            bool use_madv_populate_write)
 {
     static gsize initialized = 0;
-    MemsetContext context = {
-        .num_threads = get_memset_num_threads(hpagesize, numpages, max_threads),
-    };
+    MemsetContext *context = g_malloc0(sizeof(MemsetContext));
     size_t numpages_per_thread, leftover;
     void *(*touch_fn)(void *);
-    int ret = 0, i = 0;
+    int ret, i = 0;
     char *addr = area;
 
+    /*
+     * Asynchronous preallocation is only allowed when using MADV_POPULATE_WRITE
+     * and prealloc context for thread placement.
+     */
+    if (!use_madv_populate_write || !tc) {
+        async = false;
+    }
+
+    context->num_threads =
+        get_memset_num_threads(hpagesize, numpages, max_threads);
+
     if (g_once_init_enter(&initialized)) {
         qemu_mutex_init(&page_mutex);
         qemu_cond_init(&page_cond);
@@ -432,8 +462,11 @@ static int touch_all_pages(char *area, size_t hpagesize, size_t numpages,
     }
 
     if (use_madv_populate_write) {
-        /* Avoid creating a single thread for MADV_POPULATE_WRITE */
-        if (context.num_threads == 1) {
+        /*
+         * Avoid creating a single thread for MADV_POPULATE_WRITE when
+         * preallocating synchronously.
+         */
+        if (context->num_threads == 1 && !async) {
             if (qemu_madvise(area, hpagesize * numpages,
                              QEMU_MADV_POPULATE_WRITE)) {
                 return -errno;
@@ -445,50 +478,86 @@ static int touch_all_pages(char *area, size_t hpagesize, size_t numpages,
         touch_fn = do_touch_pages;
     }
 
-    context.threads = g_new0(MemsetThread, context.num_threads);
-    numpages_per_thread = numpages / context.num_threads;
-    leftover = numpages % context.num_threads;
-    for (i = 0; i < context.num_threads; i++) {
-        context.threads[i].addr = addr;
-        context.threads[i].numpages = numpages_per_thread + (i < leftover);
-        context.threads[i].hpagesize = hpagesize;
-        context.threads[i].context = &context;
+    context->threads = g_new0(MemsetThread, context->num_threads);
+    numpages_per_thread = numpages / context->num_threads;
+    leftover = numpages % context->num_threads;
+    for (i = 0; i < context->num_threads; i++) {
+        context->threads[i].addr = addr;
+        context->threads[i].numpages = numpages_per_thread + (i < leftover);
+        context->threads[i].hpagesize = hpagesize;
+        context->threads[i].context = context;
         if (tc) {
-            thread_context_create_thread(tc, &context.threads[i].pgthread,
+            thread_context_create_thread(tc, &context->threads[i].pgthread,
                                          "touch_pages",
-                                         touch_fn, &context.threads[i],
+                                         touch_fn, &context->threads[i],
                                          QEMU_THREAD_JOINABLE);
         } else {
-            qemu_thread_create(&context.threads[i].pgthread, "touch_pages",
-                               touch_fn, &context.threads[i],
+            qemu_thread_create(&context->threads[i].pgthread, "touch_pages",
+                               touch_fn, &context->threads[i],
                                QEMU_THREAD_JOINABLE);
         }
-        addr += context.threads[i].numpages * hpagesize;
+        addr += context->threads[i].numpages * hpagesize;
+    }
+
+    if (async) {
+        /*
+         * async requests currently require the BQL. Add it to the list and kick
+         * preallocation off during qemu_finish_async_prealloc_mem().
+         */
+        assert(bql_locked());
+        QLIST_INSERT_HEAD(&memset_contexts, context, next);
+        return 0;
     }
 
     if (!use_madv_populate_write) {
-        sigbus_memset_context = &context;
+        sigbus_memset_context = context;
     }
 
     qemu_mutex_lock(&page_mutex);
-    context.all_threads_created = true;
+    context->all_threads_created = true;
     qemu_cond_broadcast(&page_cond);
     qemu_mutex_unlock(&page_mutex);
 
-    for (i = 0; i < context.num_threads; i++) {
-        int tmp = (uintptr_t)qemu_thread_join(&context.threads[i].pgthread);
+    ret = wait_and_free_mem_prealloc_context(context);
 
+    if (!use_madv_populate_write) {
+        sigbus_memset_context = NULL;
+    }
+    return ret;
+}
+
+bool qemu_finish_async_prealloc_mem(Error **errp)
+{
+    int ret = 0, tmp;
+    MemsetContext *context, *next_context;
+
+    /* Waiting for preallocation requires the BQL. */
+    assert(bql_locked());
+    if (QLIST_EMPTY(&memset_contexts)) {
+        return true;
+    }
+
+    qemu_mutex_lock(&page_mutex);
+    QLIST_FOREACH(context, &memset_contexts, next) {
+        context->all_threads_created = true;
+    }
+    qemu_cond_broadcast(&page_cond);
+    qemu_mutex_unlock(&page_mutex);
+
+    QLIST_FOREACH_SAFE(context, &memset_contexts, next, next_context) {
+        QLIST_REMOVE(context, next);
+        tmp = wait_and_free_mem_prealloc_context(context);
         if (tmp) {
             ret = tmp;
         }
     }
 
-    if (!use_madv_populate_write) {
-        sigbus_memset_context = NULL;
+    if (ret) {
+        error_setg_errno(errp, -ret,
+                         "qemu_prealloc_mem: preallocating memory failed");
+        return false;
     }
-    g_free(context.threads);
-
-    return ret;
+    return true;
 }
 
 static bool madv_populate_write_possible(char *area, size_t pagesize)
@@ -498,7 +567,7 @@ static bool madv_populate_write_possible(char *area, size_t pagesize)
 }
 
 bool qemu_prealloc_mem(int fd, char *area, size_t sz, int max_threads,
-                       ThreadContext *tc, Error **errp)
+                       ThreadContext *tc, bool async, Error **errp)
 {
     static gsize initialized;
     int ret;
@@ -540,7 +609,7 @@ bool qemu_prealloc_mem(int fd, char *area, size_t sz, int max_threads,
     }
 
     /* touch pages simultaneously */
-    ret = touch_all_pages(area, hpagesize, numpages, max_threads, tc,
+    ret = touch_all_pages(area, hpagesize, numpages, max_threads, tc, async,
                           use_madv_populate_write);
     if (ret) {
         error_setg_errno(errp, -ret,