Linux Virtualization - May 2018 - [PATCH net 2/4] virtio-net: correctly transmit XDP buff after linearizing

Hi:

Please review the patches that tries to fix sevreal issues of
virtio-net mergeable XDP.

Thanks

Jason Wang (4):
  virtio-net: correctly redirect linearized packet
  virtio-net: correctly transmit XDP buff after linearizing
  virtio-net: reset num_buf to 1 after linearizing packet
  virito-net: fix leaking page for gso packet during mergeable XDP

 drivers/net/virtio_net.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

-- 
2.7.4

After a linearized packet was redirected by XDP, we should not go for
the err path which will try to pop buffers for the next packet and
increase the drop counter. Fixing this by just drop the page refcnt
for the original page.

Fixes: 186b3c998c50 ("virtio-net: support XDP_REDIRECT")
Reported-by: David Ahern <dsahern at gmail.com>
Tested-by: David Ahern <dsahern at gmail.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 770422e..c15d240 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -787,7 +787,7 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 			}
 			*xdp_xmit = true;
 			if (unlikely(xdp_page != page))
-				goto err_xdp;
+				put_page(page);
 			rcu_read_unlock();
 			goto xdp_xmit;
 		default:
-- 
2.7.4

We should not go for the error path after successfully transmitting a
XDP buffer after linearizing. Since the error path may try to pop and
drop next packet and increase the drop counters. Fixing this by simply
drop the refcnt of original page and go for xmit path.

Fixes: 72979a6c3590 ("virtio_net: xdp, add slowpath case for non contiguous
buffers")
Cc: John Fastabend <john.fastabend at gmail.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c15d240..6260d65 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -775,7 +775,7 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 			}
 			*xdp_xmit = true;
 			if (unlikely(xdp_page != page))
-				goto err_xdp;
+				put_page(page);
 			rcu_read_unlock();
 			goto xdp_xmit;
 		case XDP_REDIRECT:
-- 
2.7.4

If we successfully linearize the packets, num_buf were set to zero
which was wrong since we now have only 1 buffer to be used for e.g in
the error path of receive_mergeable(). Zero num_buf will lead the code
try to pop the buffers of next packet and drop it. Fixing this by set
num_buf to 1 if we successfully linearize the packet.

Fixes: 4941d472bf95 ("virtio-net: do not reset during XDP set")
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 6260d65..165a922 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -722,6 +722,7 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 						      &len);
 			if (!xdp_page)
 				goto err_xdp;
+			num_buf = 1;
 			offset = VIRTIO_XDP_HEADROOM;
 		} else {
 			xdp_page = page;
-- 
2.7.4

We need to drop refcnt to xdp_page if we see a gso packet. Otherwise
it will be leaked. Fixing this by moving the check of gso packet above
the linearizing logic.

Cc: John Fastabend <john.fastabend at gmail.com>
Fixes: 72979a6c3590 ("virtio_net: xdp, add slowpath case for non contiguous
buffers")
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 165a922..f8db809 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -707,6 +707,14 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 		void *data;
 		u32 act;
 
+		/* Transient failure which in theory could occur if
+		 * in-flight packets from before XDP was enabled reach
+		 * the receive path after XDP is loaded. In practice I
+		 * was not able to create this condition.
+		 */
+		if (unlikely(hdr->hdr.gso_type))
+			goto err_xdp;
+
 		/* This happens when rx buffer size is underestimated
 		 * or headroom is not enough because of the buffer
 		 * was refilled before XDP is set. This should only
@@ -728,14 +736,6 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 			xdp_page = page;
 		}
 
-		/* Transient failure which in theory could occur if
-		 * in-flight packets from before XDP was enabled reach
-		 * the receive path after XDP is loaded. In practice I
-		 * was not able to create this condition.
-		 */
-		if (unlikely(hdr->hdr.gso_type))
-			goto err_xdp;
-
 		/* Allow consuming headroom but reserve enough space to push
 		 * the descriptor on if we get an XDP_TX return code.
 		 */
-- 
2.7.4

On Mon, May 21, 2018 at 04:35:05PM +0800, Jason Wang
wrote:
> If we successfully linearize the packets, num_buf were set to zero
> which was wrong since we now have only 1 buffer to be used for e.g in
> the error path of receive_mergeable(). Zero num_buf will lead the code
> try to pop the buffers of next packet and drop it. Fixing this by set
> num_buf to 1 if we successfully linearize the packet.
> 
> Fixes: 4941d472bf95 ("virtio-net: do not reset during XDP set")
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6260d65..165a922 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -722,6 +722,7 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  						      &len);
>  			if (!xdp_page)
>  				goto err_xdp;
> +			num_buf = 1;
So this is tweaked here for the benefit of err_skb below.
That's confusing and we won't remember to change it
if we change the error handling.

How about fixing the error path?


-        while (--num_buf) {
+        while (num_buf-- > 1) {

Seems more robust to me.

>  			offset = VIRTIO_XDP_HEADROOM;
>  		} else {
>  			xdp_page = page;
> -- 
> 2.7.4

On Mon, May 21, 2018 at 04:35:06PM +0800, Jason Wang
wrote:
> We need to drop refcnt to xdp_page if we see a gso packet. Otherwise
> it will be leaked. Fixing this by moving the check of gso packet above
> the linearizing logic.
> 
> Cc: John Fastabend <john.fastabend at gmail.com>
> Fixes: 72979a6c3590 ("virtio_net: xdp, add slowpath case for non
contiguous buffers")
> Signed-off-by: Jason Wang <jasowang at redhat.com>
typo in subject
> ---
>  drivers/net/virtio_net.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 165a922..f8db809 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -707,6 +707,14 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  		void *data;
>  		u32 act;
>  
> +		/* Transient failure which in theory could occur if
> +		 * in-flight packets from before XDP was enabled reach
> +		 * the receive path after XDP is loaded. In practice I
> +		 * was not able to create this condition.
BTW we should probably drop the last sentence. It says in theory, should be
enough.
> +		 */
> +		if (unlikely(hdr->hdr.gso_type))
> +			goto err_xdp;
> +
>  		/* This happens when rx buffer size is underestimated
>  		 * or headroom is not enough because of the buffer
>  		 * was refilled before XDP is set. This should only
> @@ -728,14 +736,6 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  			xdp_page = page;
>  		}
>  
> -		/* Transient failure which in theory could occur if
> -		 * in-flight packets from before XDP was enabled reach
> -		 * the receive path after XDP is loaded. In practice I
> -		 * was not able to create this condition.
> -		 */
> -		if (unlikely(hdr->hdr.gso_type))
> -			goto err_xdp;
> -
>  		/* Allow consuming headroom but reserve enough space to push
>  		 * the descriptor on if we get an XDP_TX return code.
>  		 */
> -- 
> 2.7.4

On Mon, May 21, 2018 at 04:35:03PM +0800, Jason Wang
wrote:
> After a linearized packet was redirected by XDP, we should not go for
> the err path which will try to pop buffers for the next packet and
> increase the drop counter. Fixing this by just drop the page refcnt
> for the original page.
> 
> Fixes: 186b3c998c50 ("virtio-net: support XDP_REDIRECT")
> Reported-by: David Ahern <dsahern at gmail.com>
> Tested-by: David Ahern <dsahern at gmail.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  drivers/net/virtio_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 770422e..c15d240 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -787,7 +787,7 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  			}
>  			*xdp_xmit = true;
>  			if (unlikely(xdp_page != page))
> -				goto err_xdp;
> +				put_page(page);
>  			rcu_read_unlock();
>  			goto xdp_xmit;
>  		default:
> -- 
> 2.7.4

On Mon, May 21, 2018 at 04:35:04PM +0800, Jason Wang
wrote:
> We should not go for the error path after successfully transmitting a
> XDP buffer after linearizing. Since the error path may try to pop and
> drop next packet and increase the drop counters. Fixing this by simply
> drop the refcnt of original page and go for xmit path.
> 
> Fixes: 72979a6c3590 ("virtio_net: xdp, add slowpath case for non
contiguous buffers")
> Cc: John Fastabend <john.fastabend at gmail.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  drivers/net/virtio_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c15d240..6260d65 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -775,7 +775,7 @@ static struct sk_buff *receive_mergeable(struct
net_device *dev,
>  			}
>  			*xdp_xmit = true;
>  			if (unlikely(xdp_page != page))
> -				goto err_xdp;
> +				put_page(page);
>  			rcu_read_unlock();
>  			goto xdp_xmit;
>  		case XDP_REDIRECT:
> -- 
> 2.7.4

On Mon, May 21, 2018 at 04:35:02PM +0800, Jason Wang
wrote:
> Hi:
> 
> Please review the patches that tries to fix sevreal issues of
> virtio-net mergeable XDP.
> 
> Thanks
I think we should do 3/4 differently.
The rest looks good, and probably needed on stable.

Thanks!
> Jason Wang (4):
>   virtio-net: correctly redirect linearized packet
>   virtio-net: correctly transmit XDP buff after linearizing
>   virtio-net: reset num_buf to 1 after linearizing packet
>   virito-net: fix leaking page for gso packet during mergeable XDP
> 
>  drivers/net/virtio_net.c | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
> 
> -- 
> 2.7.4