Messages in this thread | | | Subject | Re: [PATCH net] virtio-net: unbreak cusmed packet for small buffer XDP | From | Jason Wang <> | Date | Tue, 4 Jul 2017 20:20:00 +0800 |
| |
On 2017年07月04日 01:03, Michael S. Tsirkin wrote: > 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: >>> On Wed, Jun 28, 2017 at 11:40:30AM +0800, Jason Wang wrote: >>>> On 2017年06月28日 11:31, Michael S. Tsirkin wrote: >>>>> 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: >>>>>>> On Wed, Jun 28, 2017 at 10:14:34AM +0800, Jason Wang wrote: >>>>>>>> On 2017年06月28日 10:02, Michael S. Tsirkin wrote: >>>>>>>>> On Wed, Jun 28, 2017 at 09:54:03AM +0800, Jason Wang wrote: >>>>>>>>>> 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.
Any reason to do this? (Looks like I don't see any code for this)
> > Could you pls explain how to reproduce the issue you are seeing? >
Using small buffer, all csumed packets will be dropped.
Thanks
| |