Re: [PATCH v1 0/2] vhost: Handle vrings crossing virtio-mem slots

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Sep 09, 2026 at 03:59:21PM +0300, Alex Fishman wrote:
> Virtio-mem dynamic memslots are intentionally exposed as separate memory
> regions. If a guest places a vring part across two adjacent slots, a later
> memory update fails vhost ring verification because the complete ring part
> is not contained in one vhost memory region.

when does this happen?

> Coalesce coherent adjacent sections only when a descriptor table,
> available ring, or used ring crosses their boundary. Unrelated
> unmergeable sections remain separate so they can still be updated
> independently.
> 
> Patch 2 adds an end-to-end qtest reproducer using a fake vhost-user
> backend and virtio-mem dynamic memslots. It also verifies that a newly
> activated slot is not folded into the merge required by the crossing
> vring.
> 
> Tested with the vhost-user/mem-slots/boundary qtest.
> 
> Buglink: https://redhat.atlassian.net/browse/RHEL-146583
> 
> Alex Fishman (2):
>   vhost: coalesce unmergeable sections across vring boundaries
>   tests/qtest: Add vhost-user memslot boundary test
> 
>  hw/virtio/vhost.c             |  72 ++++++-
>  tests/qtest/vhost-user-test.c | 395 +++++++++++++++++++++++++++++++++-
>  2 files changed, 452 insertions(+), 15 deletions(-)
> 
> 
> base-commit: ff1d2d19d7e24893e2012d879f8e73077e17b9bd
> -- 
> 2.52.0