From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net] virtio-net: unbreak cusmed packet for small buffer XDP Date: Mon, 3 Jul 2017 20:03:57 +0300 Message-ID: <20170703195752-mutt-send-email-mst@kernel.org> References: <1498614843-8163-1-git-send-email-jasowang@redhat.com> <20170628050057-mutt-send-email-mst@kernel.org> <7068053c-50da-6779-5ff2-6588e01e616d@redhat.com> <20170628051555-mutt-send-email-mst@kernel.org> <69907228-fc1b-175f-f6cd-7ac332e318be@redhat.com> <20170628063033-mutt-send-email-mst@kernel.org> <51f4c402-6a02-9bad-6dab-563ca72f431a@redhat.com> <20170628065126-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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 > > > > > > > > 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