Re: [dpdk-dev] [PATCH] vhost: fix wrong IOTLB initialization

[David Marchand <david.marchand@redhat.com>]

On Thu, May 13, 2021 at 2:38 PM Chenbo Xia <chenbo.xia@intel.com> wrote:
>
> This patch fixes an issue of application crash because of vhost iotlb
> not initialized when virtio has multiqueue enabled.
>
> iotlb messages will be sent when some queues are not enabled. If we
> initialize iotlb in vhost_user_set_vring_num, it could happen that
> iotlb update comes when iotlb pool of disabled queues are not
> initialized.

This makes the problem I reproduced disappear at init, but I noticed
the segfault after restarting testpmd once.
And a little bit after this, my vm crashed.

This is not systematic, so I guess there is some condition with how
the virtio device is initialised in the vm.


One question below.


Bugzilla ID: 703

> Fixes: 968bbc7e2e50 ("vhost: avoid IOTLB mempool allocation while IOMMU disabled")
>

Reported-by: Pei Zhang <pezhang@redhat.com>

> Signed-off-by: Chenbo Xia <chenbo.xia@intel.com>
> ---
>  lib/vhost/vhost_user.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> index 611ff209e3..ae4df8eb69 100644
> --- a/lib/vhost/vhost_user.c
> +++ b/lib/vhost/vhost_user.c
> @@ -311,6 +311,7 @@ vhost_user_set_features(struct virtio_net **pdev, struct VhostUserMsg *msg,
>         uint64_t features = msg->payload.u64;
>         uint64_t vhost_features = 0;
>         struct rte_vdpa_device *vdpa_dev;
> +       uint32_t i;
>
>         if (validate_msg_fds(msg, 0) != 0)
>                 return RTE_VHOST_MSG_RESULT_ERR;
> @@ -389,6 +390,14 @@ vhost_user_set_features(struct virtio_net **pdev, struct VhostUserMsg *msg,
>                 vdpa_dev->ops->set_features(dev->vid);
>
>         dev->flags &= ~VIRTIO_DEV_FEATURES_FAILED;
> +
> +       if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM)) {
> +               for (i = 0; i < dev->nr_vring; i++) {

I don't know the vhost-user protocol.
At this point of the device init/life, are we sure nr_vring is set to
the max number of vring?
The logs I have tend to say it is the case, but is there a guarantee
in the protocol?


Another way to fix would be to allocate on the first
VHOST_USER_IOTLB_MSG message received for a vring.


> +                       if (vhost_user_iotlb_init(dev, i))
> +                               return RTE_VHOST_MSG_RESULT_ERR;
> +               }
> +       }
> +
>         return RTE_VHOST_MSG_RESULT_OK;
>  }
>


-- 
David Marchand