On Wed, Jun 28, 2017 at 08:05:06PM +0800, Jason Wang wrote:

On 2017年06月28日 12:01, Michael S. Tsirkin wrote:

quoted

On Wed, Jun 28, 2017 at 11:40:30AM +0800, Jason Wang wrote:

quoted

On 2017年06月28日 11:31, Michael S. Tsirkin wrote:

quoted

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

quoted

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

Yes, but the comment said:

"
CKSUM_NONE:
  *
  *   The skb was already checksummed by the protocol, or a checksum is not
  *   required.
  *
  * CHECKSUM_UNNECESSARY:
  *
  *   This has the same meaning on as CHECKSUM_NONE for checksum offload on
  *   output.
  *
"

So still correct I think?

Thanks

Hmm maybe I mean NEEDS_CHECKSUM actually.

I'll need to re-read the spec.

Not sure this is an issue. But if it is, we can probably checksum the packet
before passing it to XDP. But it would be a little slow.

Thanks

Right. I confused DATA_VALID with NEEDS_CHECKSUM.

IIUC XDP generally refuses to attach if checksum offload
is enabled.

Could you pls explain how to reproduce the issue you are seeing?

-- 
MST