Re: [PATCH v4] vhost/user: clear ring addresses when getting vring base

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 11/27/24 3:03 AM, Jianping Zhao wrote:
> Clear ring addresses during vring base retrieval to handle guest reboot
> scenarios correctly. This is particularly important for vdpa-blk devices
> where the following issue occurs:
> 
> When a guest OS with vdpa-blk device reboots, during UEFI stage, only
> one vring is actually used and configured. However, QEMU still sends
> enable messages for all configured queues. The remaining queues retain
> their addresses from before reboot, which reference invalid memory
> mappings in the rebooted guest.
> 
> The issue manifests in vq_is_ready():
> 
> static bool
> vq_is_ready(struct virtio_net *dev, struct vhost_virtqueue *vq)
> {
>      /* Only checks pointer validity, not address freshness */
>      rings_ok = vq->desc && vq->avail && vq->used;
>      ...
> }
> 
> vq_is_ready() incorrectly considers these queues as ready because it
> only checks if desc/avail/used pointers are non-NULL, but cannot
> detect that these addresses are stale from the previous boot.
> 
> Clear the ring addresses in vhost_user_get_vring_base() to force
> the guest driver to reconfigure them before use. This ensures that
> vq_is_ready() will return false for queues with stale addresses
> until they are properly reconfigured by the guest driver.
> 
> Fixes: 3ea7052f4b1b ("vhost: postpone rings addresses translation")
> 
> Signed-off-by: Jianping Zhao <zhao305149619@gmail.com>
> ---
>   lib/vhost/vhost_user.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> index 6d92ad904e..52d8078d7c 100644
> --- a/lib/vhost/vhost_user.c
> +++ b/lib/vhost/vhost_user.c
> @@ -2277,6 +2277,7 @@ vhost_user_get_vring_base(struct virtio_net **pdev,
>   
>   	rte_rwlock_write_lock(&vq->access_lock);
>   	vring_invalidate(dev, vq);
> +	memset(&vq->ring_addrs, 0, sizeof(struct vhost_vring_addr));
>   	rte_rwlock_write_unlock(&vq->access_lock);
>   
>   	return RTE_VHOST_MSG_RESULT_REPLY;

Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks,
Maxime