Re: [PATCH V2 4/9] vhost: reset invalidate_count in vhost_set_vring_num_addr()

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Jul 31, 2019 at 04:46:50AM -0400, Jason Wang wrote:
> The vhost_set_vring_num_addr() could be called in the middle of
> invalidate_range_start() and invalidate_range_end(). If we don't reset
> invalidate_count after the un-registering of MMU notifier, the
> invalidate_cont will run out of sync (e.g never reach zero). This will
> in fact disable the fast accessor path. Fixing by reset the count to
> zero.
> 
> Reported-by: Michael S. Tsirkin <mst@redhat.com>

Did Michael report this as well?

> Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
> Signed-off-by: Jason Wang <jasowang@redhat.com>
>  drivers/vhost/vhost.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 2a3154976277..2a7217c33668 100644
> +++ b/drivers/vhost/vhost.c
> @@ -2073,6 +2073,10 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
>  		d->has_notifier = false;
>  	}
>  
> +	/* reset invalidate_count in case we are in the middle of
> +	 * invalidate_start() and invalidate_end().
> +	 */
> +	vq->invalidate_count = 0;
>  	vhost_uninit_vq_maps(vq);
>  #endif
>