On Wed, Jun 28, 2017 at 10:45:18AM +0800, Jason Wang wrote:

On 2017年06月28日 10:17, Michael S. Tsirkin wrote:

quoted

On Wed, Jun 28, 2017 at 10:14:34AM +0800, Jason Wang wrote:

quoted

On 2017年06月28日 10:02, Michael S. Tsirkin wrote:

quoted

On Wed, Jun 28, 2017 at 09:54:03AM +0800, Jason Wang wrote:

quoted

We should allow csumed packet for small buffer, otherwise XDP_PASS
won't work correctly.

Fixes commit bb91accf2733 ("virtio-net: XDP support for small buffers")
Signed-off-by: Jason Wang <jasowang@redhat.com>

The issue would be VIRTIO_NET_HDR_F_DATA_VALID might be set.
What do you think?

I think it's safe. For XDP_PASS, it work like in the past.

That's the part I don't get. With DATA_VALID csum in packet is wrong, XDP
tools assume it's value.

DATA_VALID is CHECKSUM_UNCESSARY on the host, and according to the comment
in skbuff.h


"
 *   The hardware you're dealing with doesn't calculate the full checksum
 *   (as in CHECKSUM_COMPLETE), but it does parse headers and verify
checksums
 *   for specific protocols. For such packets it will set
CHECKSUM_UNNECESSARY
 *   if their checksums are okay. skb->csum is still undefined in this case
 *   though. A driver or device must never modify the checksum field in the
 *   packet even if checksum is verified.
"

The csum is correct I believe?

Thanks

That's on input. But I think for tun it's output, where that is equivalent
to CHECKSUM_NONE

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quoted

For XDP_TX, we
zero the vnet header.

Again TX offload is disabled, so packets will go out with an invalid
checksum.

quoted

For adjusting header, XDP prog should deal with csum.

Thanks

That part seems right.

quoted

quoted

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---
The patch is needed for -stable.
---
   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 143d8a9..499fcc9 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -413,7 +413,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
   		void *orig_data;
   		u32 act;
-		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
+		if (unlikely(hdr->hdr.gso_type))
   			goto err_xdp;
   		xdp.data_hard_start = buf + VIRTNET_RX_PAD + vi->hdr_len;

-- 
2.7.4

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