The spec states:
  "The device MUST set addr, region_size, usable_region_size, plugged_size,
   requested_size to multiples of block_size."

With block sizes > 256MB, we currently wouldn't guarantee that for the
usable_region_size.

Note that we cannot exceed the region_size, as we already enforce the
alignment there properly.

Fixes: 910b25766b33 ("virtio-mem: Paravirtualized memory hot(un)plug")
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/virtio/virtio-mem.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index 70200b4eac..461ac68ee8 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -227,6 +227,9 @@ static void virtio_mem_resize_usable_region(VirtIOMEM *vmem,
     uint64_t newsize = MIN(memory_region_size(&vmem->memdev->mr),
                            requested_size + VIRTIO_MEM_USABLE_EXTENT);
 
+    /* The usable region size always has to be multiples of the block size. */
+    newsize = QEMU_ALIGN_UP(newsize, vmem->block_size);
+
     if (!requested_size) {
         newsize = 0;
     }
-- 
2.26.2