Just having a file descriptor is not enough to consider a memory region public. If QEMU didn't map it as MAP_SHARED (in case of share=off), guest writes to this region won't be visible to the vhost-user backend, thus causing it to read all zeroes or garbage. Make sure we don't pass such regions and include that to our definition of what a private region is.
Signed-off-by: Daniil Tatianin <[email protected]> --- hw/virtio/vhost.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index 266a11514a..eb098a25c5 100644 --- a/hw/virtio/vhost.c +++ b/hw/virtio/vhost.c @@ -591,11 +591,13 @@ static bool vhost_section(struct vhost_dev *dev, MemoryRegionSection *section) /* * Some backends (like vhost-user) can only handle memory regions * that have an fd (can be mapped into a different process). Filter - * the ones without an fd out, if requested. - * - * TODO: we might have to limit to MAP_SHARED as well. + * the ones without an fd out, if requested. Also make sure that + * this region is mapped as shared so that the vhost backend can + * observe modifications to this region, otherwise we consider it + * private. */ - if (memory_region_get_fd(section->mr) < 0 && + if ((memory_region_get_fd(section->mr) < 0 || + !qemu_ram_is_shared(section->mr->ram_block)) && dev->vhost_ops->vhost_backend_no_private_memslots && dev->vhost_ops->vhost_backend_no_private_memslots(dev)) { trace_vhost_reject_section(mr->name, 2); -- 2.34.1
