[PATCH v1 1/2] virtio-mem: Warn if a memory backend with "prealloc=on" is used

[David Hildenbrand <david@redhat.com>]

"prealloc=on" for the memory backend does not work as expected, as
virtio-mem will simply discard all preallocated memory immediately again.
In the best case, it's an expensive NOP. In the worst case, it's an
unexpected allocation error.

Instead, "prealloc=on" should be specified for the virtio-mem device only,
such that virtio-mem will try preallocating memory before plugging
memory dynamically to the guest.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/virtio/virtio-mem.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index 04c223b0c9..6c337db0a7 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -765,6 +765,13 @@ static void virtio_mem_device_realize(DeviceState *dev, Error **errp)
         return;
     }
 
+    if (vmem->memdev->prealloc) {
+        warn_report("'%s' property specifies a memdev with preallocation"
+                    " enabled: %s. Instead, specify 'prealloc=on' for the"
+                    " virtio-mem device. ", VIRTIO_MEM_MEMDEV_PROP,
+                    object_get_canonical_path_component(OBJECT(vmem->memdev)));
+    }
+
     if ((nb_numa_nodes && vmem->node >= nb_numa_nodes) ||
         (!nb_numa_nodes && vmem->node)) {
         error_setg(errp, "'%s' property has value '%" PRIu32 "', which exceeds"
-- 
2.34.1