[PATCH v2] vhost: fix deadlock during software live migration of VDPA in a nested virtualization environment

[Maxime Coquelin]

On 1/22/24 04:27, Hao Chen wrote:
> In a nested virtualization environment, running dpdk-vdpa in QEMU-L1 for
> software live migration will result in a deadlock between dpdke-vdpa and
> QEMU-L2 processes.
> 'rte_vdpa_relay_vring_used'->
> '__vhost_iova_to_vva'->
> 'vhost_user_iotlb_rd_unlock(vq)'->
> 'vhost_user_iotlb_miss'-> send vhost message 'VHOST_USER_SLAVE_IOTLB_MSG'
> to QEMU-L2's vdpa socket,
> then call 'vhost_user_iotlb_rd_lock(vq)' to hold the read lock `iotlb_lock`.
> But there is no place to release this read lock.
> 
> QEMU-L2 get the 'VHOST_USER_SLAVE_IOTLB_MSG',
> then call 'vhost_user_send_device_iotlb_msg' to send 'VHOST_USER_IOTLB_MSG'
> messages to dpdk-vdpa.
> Dpdk-vdpa will call vhost_user_iotlb_msg->
> vhost_user_iotlb_cache_insert, here, will obtain the write lock
> `iotlb_lock`, but the read lock `iotlb_lock` has not been released and
> will block here.
> 
> This patch add lock and unlock function to fix the deadlock.
> 
> Fixes: b13ad2decc83 ("vhost: provide helpers for virtio ring relay")
> Cc: stable at dpdk.org
> 
> Signed-off-by: Hao Chen <chenh at yusur.tech>
> ---
> Changes v1 ... v2:
> - protect the vhost_alloc_copy_ind_table() call too.
> 


Applied to next-virtio tree with reworked commit message.

Thanks,
Maxime