virtio-mem: Migration sanity checks

We want to make sure that certain properties don't change during
migration, especially to catch user errors in a nice way. Let's migrate
a temporary structure and validate that the properties didn't change.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200626072248.78761-19-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-mem.c

@@ -519,12 +519,82 @@ static int virtio_mem_post_load(void *opaque, int version_id)
     return virtio_mem_restore_unplugged(VIRTIO_MEM(opaque));
 }
 
+typedef struct VirtIOMEMMigSanityChecks {
+    VirtIOMEM *parent;
+    uint64_t addr;
+    uint64_t region_size;
+    uint64_t block_size;
+    uint32_t node;
+} VirtIOMEMMigSanityChecks;
+
+static int virtio_mem_mig_sanity_checks_pre_save(void *opaque)
+{
+    VirtIOMEMMigSanityChecks *tmp = opaque;
+    VirtIOMEM *vmem = tmp->parent;
+
+    tmp->addr = vmem->addr;
+    tmp->region_size = memory_region_size(&vmem->memdev->mr);
+    tmp->block_size = vmem->block_size;
+    tmp->node = vmem->node;
+    return 0;
+}
+
+static int virtio_mem_mig_sanity_checks_post_load(void *opaque, int version_id)
+{
+    VirtIOMEMMigSanityChecks *tmp = opaque;
+    VirtIOMEM *vmem = tmp->parent;
+    const uint64_t new_region_size = memory_region_size(&vmem->memdev->mr);
+
+    if (tmp->addr != vmem->addr) {
+        error_report("Property '%s' changed from 0x%" PRIx64 " to 0x%" PRIx64,
+                     VIRTIO_MEM_ADDR_PROP, tmp->addr, vmem->addr);
+        return -EINVAL;
+    }
+    /*
+     * Note: Preparation for resizeable memory regions. The maximum size
+     * of the memory region must not change during migration.
+     */
+    if (tmp->region_size != new_region_size) {
+        error_report("Property '%s' size changed from 0x%" PRIx64 " to 0x%"
+                     PRIx64, VIRTIO_MEM_MEMDEV_PROP, tmp->region_size,
+                     new_region_size);
+        return -EINVAL;
+    }
+    if (tmp->block_size != vmem->block_size) {
+        error_report("Property '%s' changed from 0x%" PRIx64 " to 0x%" PRIx64,
+                     VIRTIO_MEM_BLOCK_SIZE_PROP, tmp->block_size,
+                     vmem->block_size);
+        return -EINVAL;
+    }
+    if (tmp->node != vmem->node) {
+        error_report("Property '%s' changed from %" PRIu32 " to %" PRIu32,
+                     VIRTIO_MEM_NODE_PROP, tmp->node, vmem->node);
+        return -EINVAL;
+    }
+    return 0;
+}
+
+static const VMStateDescription vmstate_virtio_mem_sanity_checks = {
+    .name = "virtio-mem-device/sanity-checks",
+    .pre_save = virtio_mem_mig_sanity_checks_pre_save,
+    .post_load = virtio_mem_mig_sanity_checks_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT64(addr, VirtIOMEMMigSanityChecks),
+        VMSTATE_UINT64(region_size, VirtIOMEMMigSanityChecks),
+        VMSTATE_UINT64(block_size, VirtIOMEMMigSanityChecks),
+        VMSTATE_UINT32(node, VirtIOMEMMigSanityChecks),
+        VMSTATE_END_OF_LIST(),
+    },
+};
+
 static const VMStateDescription vmstate_virtio_mem_device = {
     .name = "virtio-mem-device",
     .minimum_version_id = 1,
     .version_id = 1,
     .post_load = virtio_mem_post_load,
     .fields = (VMStateField[]) {
+        VMSTATE_WITH_TMP(VirtIOMEM, VirtIOMEMMigSanityChecks,
+                         vmstate_virtio_mem_sanity_checks),
         VMSTATE_UINT64(usable_region_size, VirtIOMEM),
         VMSTATE_UINT64(size, VirtIOMEM),
         VMSTATE_UINT64(requested_size, VirtIOMEM),