Re: [PATCH v3 3/3] vhost: Don't call log_access_ok() when using IOTLB

[Jason Wang]

On 2020/10/3 下午6:02, Greg Kurz wrote:
> When the IOTLB device is enabled, the log_guest_addr that is passed by
> userspace to the VHOST_SET_VRING_ADDR ioctl, and which is then written
> to vq->log_addr, is a GIOVA. All writes to this address are translated
> by log_user() to writes to an HVA, and then ultimately logged through
> the corresponding GPAs in log_write_hva(). No logging will ever occur
> with vq->log_addr in this case. It is thus wrong to pass vq->log_addr
> and log_guest_addr to log_access_vq() which assumes they are actual
> GPAs.
>
> Introduce a new vq_log_used_access_ok() helper that only checks accesses
> to the log for the used structure when there isn't an IOTLB device around.
>
> Signed-off-by: Greg Kurz <groug@kaod.org>


Acked-by: Jason Wang <jasowang@redhat.com>

In the future, we may consider to deprecate log_guest_addr since in any 
case regardless of IOTLB ennoblement we can get GPA from either IOTLB or 
MEM table.

Thanks


> ---
>   drivers/vhost/vhost.c |   23 ++++++++++++++++++-----
>   1 file changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 9d2c225fb518..9ad45e1d27f0 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1370,6 +1370,20 @@ bool vhost_log_access_ok(struct vhost_dev *dev)
>   }
>   EXPORT_SYMBOL_GPL(vhost_log_access_ok);
>   
> +static bool vq_log_used_access_ok(struct vhost_virtqueue *vq,
> +                                 void __user *log_base,
> +                                 bool log_used,
> +                                 u64 log_addr)
> +{
> +       /* If an IOTLB device is present, log_addr is a GIOVA that
> +        * will never be logged by log_used(). */
> +       if (vq->iotlb)
> +               return true;
> +
> +       return !log_used || log_access_ok(log_base, log_addr,
> +                                         vhost_get_used_size(vq, vq->num));
> +}
> +
>   /* Verify access for write logging. */
>   /* Caller should have vq mutex and device mutex */
>   static bool vq_log_access_ok(struct vhost_virtqueue *vq,
> @@ -1377,8 +1391,7 @@ static bool vq_log_access_ok(struct vhost_virtqueue *vq,
>   {
>         return vq_memory_access_ok(log_base, vq->umem,
>                                    vhost_has_feature(vq, VHOST_F_LOG_ALL)) &&
> -               (!vq->log_used || log_access_ok(log_base, vq->log_addr,
> -                                 vhost_get_used_size(vq, vq->num)));
> +               vq_log_used_access_ok(vq, log_base, vq->log_used, vq->log_addr);
>   }
>   
>   /* Can we start vq? */
> @@ -1517,9 +1530,9 @@ static long vhost_vring_set_addr(struct vhost_dev *d,
>                         return -EINVAL;
>   
>   		/* Also validate log access for used ring if enabled. */
> -               if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) &&
> -                       !log_access_ok(vq->log_base, a.log_guest_addr,
> -                                      vhost_get_used_size(vq, vq->num)))
> +               if (!vq_log_used_access_ok(vq, vq->log_base,
> +                               a.flags & (0x1 << VHOST_VRING_F_LOG),
> +                               a.log_guest_addr))
>                         return -EINVAL;
>         }
>