virtio-mem: Fail if a memory backend with "prealloc=on" is specified

"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. Fail if such a memory backend is

Tested-by: Michal Privoznik <>
Reviewed-by: Dr. David Alan Gilbert <>
Reviewed-by: Peter Xu <>
Reviewed-by: Michael S. Tsirkin <>
Reviewed-by: Juan Quintela <>S
Signed-off-by: David Hildenbrand <>
Signed-off-by: Juan Quintela <>
1 file changed