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

[Alex Fishman <afishman@redhat.com>]

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.

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