1 files changed, 272 insertions, 0 deletions
diff --git a/hw/i386/kvm/xen_overlay.c b/hw/i386/kvm/xen_overlay.c
new file mode 100644
index 0000000000..39fda1b72c
--- /dev/null
+++ b/hw/i386/kvm/xen_overlay.c
@@ -0,0 +1,272 @@
+/*
+ * QEMU Xen emulation: Shared/overlay pages support
+ *
+ * Copyright © 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Authors: David Woodhouse <dwmw2@infradead.org>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/host-utils.h"
+#include "qemu/module.h"
+#include "qemu/main-loop.h"
+#include "qapi/error.h"
+#include "qom/object.h"
+#include "exec/target_page.h"
+#include "exec/address-spaces.h"
+#include "migration/vmstate.h"
+
+#include "hw/sysbus.h"
+#include "hw/xen/xen.h"
+#include "xen_overlay.h"
+
+#include "sysemu/kvm.h"
+#include "sysemu/kvm_xen.h"
+#include <linux/kvm.h>
+
+#include "hw/xen/interface/memory.h"
+
+
+#define TYPE_XEN_OVERLAY "xen-overlay"
+OBJECT_DECLARE_SIMPLE_TYPE(XenOverlayState, XEN_OVERLAY)
+
+#define XEN_PAGE_SHIFT 12
+#define XEN_PAGE_SIZE (1ULL << XEN_PAGE_SHIFT)
+
+struct XenOverlayState {
+    /*< private >*/
+    SysBusDevice busdev;
+    /*< public >*/
+
+    MemoryRegion shinfo_mem;
+    void *shinfo_ptr;
+    uint64_t shinfo_gpa;
+    bool long_mode;
+};
+
+struct XenOverlayState *xen_overlay_singleton;
+
+void xen_overlay_do_map_page(MemoryRegion *page, uint64_t gpa)
+{
+    /*
+     * Xen allows guests to map the same page as many times as it likes
+     * into guest physical frames. We don't, because it would be hard
+     * to track and restore them all. One mapping of each page is
+     * perfectly sufficient for all known guests... and we've tested
+     * that theory on a few now in other implementations. dwmw2.
+     */
+    if (memory_region_is_mapped(page)) {
+        if (gpa == INVALID_GPA) {
+            memory_region_del_subregion(get_system_memory(), page);
+        } else {
+            /* Just move it */
+            memory_region_set_address(page, gpa);
+        }
+    } else if (gpa != INVALID_GPA) {
+        memory_region_add_subregion_overlap(get_system_memory(), gpa, page, 0);
+    }
+}
+
+/* KVM is the only existing back end for now. Let's not overengineer it yet. */
+static int xen_overlay_set_be_shinfo(uint64_t gfn)
+{
+    struct kvm_xen_hvm_attr xa = {
+        .type = KVM_XEN_ATTR_TYPE_SHARED_INFO,
+        .u.shared_info.gfn = gfn,
+    };
+
+    return kvm_vm_ioctl(kvm_state, KVM_XEN_HVM_SET_ATTR, &xa);
+}
+
+
+static void xen_overlay_realize(DeviceState *dev, Error **errp)
+{
+    XenOverlayState *s = XEN_OVERLAY(dev);
+
+    if (xen_mode != XEN_EMULATE) {
+        error_setg(errp, "Xen overlay page support is for Xen emulation");
+        return;
+    }
+
+    memory_region_init_ram(&s->shinfo_mem, OBJECT(dev), "xen:shared_info",
+                           XEN_PAGE_SIZE, &error_abort);
+    memory_region_set_enabled(&s->shinfo_mem, true);
+
+    s->shinfo_ptr = memory_region_get_ram_ptr(&s->shinfo_mem);
+    s->shinfo_gpa = INVALID_GPA;
+    s->long_mode = false;
+    memset(s->shinfo_ptr, 0, XEN_PAGE_SIZE);
+}
+
+static int xen_overlay_pre_save(void *opaque)
+{
+    /*
+     * Fetch the kernel's idea of long_mode to avoid the race condition
+     * where the guest has set the hypercall page up in 64-bit mode but
+     * not yet made a hypercall by the time migration happens, so qemu
+     * hasn't yet noticed.
+     */
+    return xen_sync_long_mode();
+}
+
+static int xen_overlay_post_load(void *opaque, int version_id)
+{
+    XenOverlayState *s = opaque;
+
+    if (s->shinfo_gpa != INVALID_GPA) {
+        xen_overlay_do_map_page(&s->shinfo_mem, s->shinfo_gpa);
+        xen_overlay_set_be_shinfo(s->shinfo_gpa >> XEN_PAGE_SHIFT);
+    }
+    if (s->long_mode) {
+        xen_set_long_mode(true);
+    }
+
+    return 0;
+}
+
+static bool xen_overlay_is_needed(void *opaque)
+{
+    return xen_mode == XEN_EMULATE;
+}
+
+static const VMStateDescription xen_overlay_vmstate = {
+    .name = "xen_overlay",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = xen_overlay_is_needed,
+    .pre_save = xen_overlay_pre_save,
+    .post_load = xen_overlay_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT64(shinfo_gpa, XenOverlayState),
+        VMSTATE_BOOL(long_mode, XenOverlayState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static void xen_overlay_reset(DeviceState *dev)
+{
+    kvm_xen_soft_reset();
+}
+
+static void xen_overlay_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->reset = xen_overlay_reset;
+    dc->realize = xen_overlay_realize;
+    dc->vmsd = &xen_overlay_vmstate;
+}
+
+static const TypeInfo xen_overlay_info = {
+    .name          = TYPE_XEN_OVERLAY,
+    .parent        = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(XenOverlayState),
+    .class_init    = xen_overlay_class_init,
+};
+
+void xen_overlay_create(void)
+{
+    xen_overlay_singleton = XEN_OVERLAY(sysbus_create_simple(TYPE_XEN_OVERLAY,
+                                                             -1, NULL));
+
+    /* If xen_domid wasn't explicitly set, at least make sure it isn't zero. */
+    if (xen_domid == DOMID_QEMU) {
+        xen_domid = 1;
+    };
+}
+
+static void xen_overlay_register_types(void)
+{
+    type_register_static(&xen_overlay_info);
+}
+
+type_init(xen_overlay_register_types)
+
+int xen_overlay_map_shinfo_page(uint64_t gpa)
+{
+    XenOverlayState *s = xen_overlay_singleton;
+    int ret;
+
+    if (!s) {
+        return -ENOENT;
+    }
+
+    assert(qemu_mutex_iothread_locked());
+
+    if (s->shinfo_gpa) {
+        /* If removing shinfo page, turn the kernel magic off first */
+        ret = xen_overlay_set_be_shinfo(INVALID_GFN);
+        if (ret) {
+            return ret;
+        }
+    }
+
+    xen_overlay_do_map_page(&s->shinfo_mem, gpa);
+    if (gpa != INVALID_GPA) {
+        ret = xen_overlay_set_be_shinfo(gpa >> XEN_PAGE_SHIFT);
+        if (ret) {
+            return ret;
+        }
+    }
+    s->shinfo_gpa = gpa;
+
+    return 0;
+}
+
+void *xen_overlay_get_shinfo_ptr(void)
+{
+    XenOverlayState *s = xen_overlay_singleton;
+
+    if (!s) {
+        return NULL;
+    }
+
+    return s->shinfo_ptr;
+}
+
+int xen_sync_long_mode(void)
+{
+    int ret;
+    struct kvm_xen_hvm_attr xa = {
+        .type = KVM_XEN_ATTR_TYPE_LONG_MODE,
+    };
+
+    if (!xen_overlay_singleton) {
+        return -ENOENT;
+    }
+
+    ret = kvm_vm_ioctl(kvm_state, KVM_XEN_HVM_GET_ATTR, &xa);
+    if (!ret) {
+        xen_overlay_singleton->long_mode = xa.u.long_mode;
+    }
+
+    return ret;
+}
+
+int xen_set_long_mode(bool long_mode)
+{
+    int ret;
+    struct kvm_xen_hvm_attr xa = {
+        .type = KVM_XEN_ATTR_TYPE_LONG_MODE,
+        .u.long_mode = long_mode,
+    };
+
+    if (!xen_overlay_singleton) {
+        return -ENOENT;
+    }
+
+    ret = kvm_vm_ioctl(kvm_state, KVM_XEN_HVM_SET_ATTR, &xa);
+    if (!ret) {
+        xen_overlay_singleton->long_mode = xa.u.long_mode;
+    }
+
+    return ret;
+}
+
+bool xen_is_long_mode(void)
+{
+    return xen_overlay_singleton && xen_overlay_singleton->long_mode;
+}