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| Started by | "Michael S. Tsirkin" <mst@redhat.com> |
|---|---|
| First post | 2017-07-03 19:10 +0200 |
| Last post | 2017-07-06 02:10 +0200 |
| Articles | 3 — 2 participants |
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Re: [PATCH net] virtio-net: unbreak cusmed packet for small buffer XDP "Michael S. Tsirkin" <mst@redhat.com> - 2017-07-03 19:10 +0200
Re: [PATCH net] virtio-net: unbreak cusmed packet for small buffer XDP Jason Wang <jasowang@redhat.com> - 2017-07-04 14:30 +0200
Re: [PATCH net] virtio-net: unbreak cusmed packet for small buffer XDP "Michael S. Tsirkin" <mst@redhat.com> - 2017-07-06 02:10 +0200
| From | "Michael S. Tsirkin" <mst@redhat.com> |
|---|---|
| Date | 2017-07-03 19:10 +0200 |
| Subject | Re: [PATCH net] virtio-net: unbreak cusmed packet for small buffer XDP |
| Message-ID | <tZd1f-4pZ-3@gated-at.bofh.it> |
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.
Could you pls explain how to reproduce the issue you are seeing?
--
MST
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| From | Jason Wang <jasowang@redhat.com> |
|---|---|
| Date | 2017-07-04 14:30 +0200 |
| Message-ID | <tZv7Q-89B-13@gated-at.bofh.it> |
| In reply to | #1680504 |
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
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| From | "Michael S. Tsirkin" <mst@redhat.com> |
|---|---|
| Date | 2017-07-06 02:10 +0200 |
| Message-ID | <u02wN-52u-11@gated-at.bofh.it> |
| In reply to | #1680915 |
On Tue, Jul 04, 2017 at 08:20:00PM +0800, Jason Wang wrote: > > 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) Some of it was covered here https://www.mail-archive.com/netdev@vger.kernel.org/msg162577.html -- MST
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