[PATCH v1 15/15] virtio-mem: Mark memslot alias memory regions unmergeable

[David Hildenbrand <david@redhat.com>]

Let's mark the memslot alias memory regions as unmergable, such that
flatview and vhost won't merge adjacent memory region aliases and we can
atomically map/unmap individual aliases without affecting adjacent
alias memory regions.

This fixes issues with vhost and vfio (which do not support atomic memslot
updates) and avoids the temporary removal of large memslots, which
can be an expensive operation. For example, vfio might have to unpin +
repin a lot of memory, which is undesired.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/virtio/virtio-mem.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index 516370067a..cccd834466 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -955,6 +955,12 @@ static void virtio_mem_prepare_memslots(VirtIOMEM *vmem)
         memory_region_init_alias(&vmem->memslots[idx], OBJECT(vmem), name,
                                  &vmem->memdev->mr, memslot_offset,
                                  memslot_size);
+        /*
+         * We want to be able to atomically and efficiently activate/deactivate
+         * individual memslots without affecting adjacent memslots in memory
+         * notifiers.
+         */
+        memory_region_set_unmergeable(&vmem->memslots[idx], true);
     }
 }
 
-- 
2.40.1