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Subject: Re: [virtio-comment] Re: [PATCH v4 1/2] virtio-net: update description for VIRTIO_NET_F_GUEST_CSUM.
å 2023/12/6 äå5:03, Heng Qi åé:
å 2023/12/6 äå4:46, Jason Wang åé:On Wed, Dec 6, 2023 at 4:08âPM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:On Wed, 6 Dec 2023 12:36:53 +0800, Jason Wang <jasowang@redhat.com> wrote:On Wed, Dec 6, 2023 at 10:21âAM Heng Qi <hengqi@linux.alibaba.com> wrote:å 2023/12/5 äå10:45, Michael S. Tsirkin åé:On Tue, Dec 05, 2023 at 10:18:32PM +0800, Heng Qi wrote:å 2023/12/5 äå11:52, Jason Wang åé:On Mon, Dec 4, 2023 at 5:34âPM Heng Qi <hengqi@linux.alibaba.com> wrote:I agree, we can be clear about what types of packets DATA_VALID mightå 2023/12/4 äå5:05, Michael S. Tsirkin åé:I'm not sure if this should be defined by a new FULL_CSUM feature.On Mon, Dec 04, 2023 at 04:59:49PM +0800, Jason Wang wrote:On Mon, Dec 4, 2023 at 4:53âPM Michael S. Tsirkin <mst@redhat.com> wrote:Yes, I think it is probably the headers that DATA_VALID can work. WeOn Mon, Dec 04, 2023 at 04:49:46PM +0800, Jason Wang wrote:On Mon, Dec 4, 2023 at 3:37âPM Heng Qi <hengqi@linux.alibaba.com> wrote:I feel we just need a proper definition of what does "full checksum"I'd suggest to leave it as is. As I didn't find any issue since evenå 2023/12/4 äå3:18, Jason Wang åé:On Fri, Dec 1, 2023 at 3:16âPM Heng Qi <hengqi@linux.alibaba.com> wrote:Yes, you are right, so I used "device *can*" here. Which packet typesI think DATA_VALID is optional here as device can't recognize all typeå 2023/12/1 äå3:05, Jason Wang åé:On Fri, Dec 1, 2023 at 2:30âPM Heng Qi <hengqi@linux.alibaba.com> wrote:I may miss something here, but what's the difference betweenå 2023/12/1 äå2:24, Heng Qi åé:å 2023/12/1 äå1:18, Jason Wang åé:On Wed, Nov 29, 2023 at 4:23âPM Heng Qi <hengqi@linux.alibaba.com>wrote:å 2023/11/29 äå4:00, Jason Wang åé:On Tue, Nov 28, 2023 at 4:08âPM Heng Qi <hengqi@linux.alibaba.com>wrote:To prevent readers from misunderstanding that the driver canonly handles packets with partial checksum whenVIRTIO_NET_F_GUEST_CSUM is negotiated, we update the description.Signed-off-by: Heng Qi <hengqi@linux.alibaba.com> --- device-types/net/description.tex | 2 +-ÂÂÂÂÂÂÂÂ 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/device-types/net/description.tex b/device-types/net/description.tex index aff5e08..529f470 100644 --- a/device-types/net/description.tex +++ b/device-types/net/description.tex@@ -38,7 +38,7 @@ \subsection{Feature bits}\label{sec:Device Types/ Network Device / Feature bits \begin{description}\item[VIRTIO_NET_F_CSUM (0)] Device handles packets withpartial checksum offload.-\item[VIRTIO_NET_F_GUEST_CSUM (1)] Driver handles packets withpartial checksum.+\item[VIRTIO_NET_F_GUEST_CSUM (1)] Driver handles packets withpartial checksum or full checksum.So patch 2 said "+\item[VIRTIO_NET_F_GUEST_FULL_CSUM (64)] Driver handles packets withfull checksum. \end{description} "Is there any difference between the two "full checksum" here?There's no difference.The core is that VIRTIO_NET_F_GUEST_FULL_CSUM means that the driver"can only" handle packets with full checksum.This seems to be odd.Driver can always handle packet with full checksum, no?Yes.I meant it will be then to be functional equivalent to ! VIRTIO_NET_F_GUEST_FULL_CSUM?Are you referring to "functional equivalent to !VIRTIO_NET_F_GUEST_CSUM" ?Sorry, this is a typo. I meant Are you referring to"functional equivalent to !VIRTIO_NET_F_GUEST_FULL_CSUM" ?If so, I think it's no.Maybe a description similar to the following would be more clearer:+\item[VIRTIO_NET_F_GUEST_FULL_CSUM (64)] Driver does not handlepackets with partial checksum.VIRTIO_NET_F_GUEST_FULL_CSUM and !VIRTIO_NET_F_GUEST_CSUM?ÂÂÂÂÂ From the device perspective:If !VIRTIO_NET_F_GUEST_CSUM, the device delivers packets with fullchecksum to the driver,but the device can not validate the checksum for these packets. That is,the flags in virtio-net-hdrwill not contain _DATA_VALID, and the driver or stack needs to validatethese packets.If VIRTIO_NET_F_GUEST_FULL_CSUM, the device delivers packets with fullchecksum to the driver,and the device can validate the checksum for these packets. That is, theflags in virtio-net-hdr will contain _DATA_VALID,of protocols.the device recognizes or validatesdepends on the device's implementation. This is also the currentpractice of GUEST_CSUM.and the driver or stack does not need to validate these packets.Ok, so I think there're something that is subtle here,Ok, I see.and that's why I'm asking here:1) "Driver does not handle packets with partial checksum" is notaccurate, !GUEST_CUSM also fit for this definition.2) "Driver handles packets with full checksum" is kind of ambiguous as it doesn't say whether or not the packet has been validated or not.Maybe the description below would be less subtle?+\item[VIRTIO_NET_F_GUEST_CSUM (1)] Driver handles packets with partialchecksum or full checksum.with DATA_VALID. Did you?+\item[VIRTIO_NET_F_GUEST_FULL_CSUM (64)] The driver handles packetswith full checksum, and the device optionally validates the packet's checksum.Or maybe something like (not a native speaker)The driver handles packets with full checksum which the device hasalready validated. Thanksmean in this context. It is used but not defined. Assume this feature was negotiated.My understanding is that this is just like VIRTIO_NET_F_GUEST_CSUMbut certain values in the header are then disallowed? Which? This should be in the spec.never define it in the past.E.g in the Linux we map DATA_VALID to CHECKSUM_UNNECESSARY, but it canonly work for some specific protocols: """ÂÂÂÂ *ÂÂ %CHECKSUM_UNNECESSARY is applicable to following protocols:ÂÂÂÂ * ÂÂÂÂ *ÂÂÂÂ - TCP: IPv6 and IPv4.ÂÂÂÂ *ÂÂÂÂ - UDP: IPv4 and IPv6. A device may apply CHECKSUM_UNNECESSARY to a ÂÂÂÂ *ÂÂÂÂÂÂ zero UDP checksum for either IPv4 or IPv6, the networking stackÂÂÂÂ *ÂÂÂÂÂÂ may perform further validation in this case.ÂÂÂÂ *ÂÂÂÂ - GRE: only if the checksum is present in the header. ÂÂÂÂ *ÂÂÂÂ - SCTP: indicates the CRC in SCTP header has been validated. ÂÂÂÂ *ÂÂÂÂ - FCOE: indicates the CRC in FC frame has been validated."""I'm not sure whether it's just fine to duplicate the definition orit's too late to define any now.I think it's mostly harmless for other protocols.This seems to be an issue with GUEST_CSUM.I think we should supplement these with a new patch for GUEST_CSUM?Probably. My understanding is:You want to reuse DATA_VALID here, so we need to stick to a consistentsemantic for GUEST_CUSM and FULL_CSUM. So we need a definition of "full csum" or what kind of packet could DATA_VALID work here.cover, e.g. TCP/UDP/GRE/SCTP/FoCE.But I think we also need something like \field{supported_validate_types} to indicate which packet types the device supports validating and settingDATA_VALID,otherwise the device driver that negotiates this feature may fail to livemigration. Am I right?I'm not sure how GUEST_CSUM works now as it should also suffer from theabovementioned issues with live migration, but no devices are reporting thisright now.Maybe, each device only supports checksum verification for TCP/UDP bydefault? I don't know.But I hope we can focus on this and get consensus, because our hw releasedate is coming soon. Thanks a lot!First, DATA_VALID is not a thing that hardware should ever use. It's a hack when packets are passed within host.Get here. Thanks!So if I understand correctly, we need a new flag here and define the supported protocols.For what, migration?No. It's basically a question of whether or not we want to reuse DATA_VALID. It has limitations that it only works for some specific protocols.Yes, I understand what Xuan means is that we reuse DATA_VALID and advertisewhat specific protocols DATA_VALID covers.Back to supported_validate_types, now I think we really don't need to let the device provide this field. Why? Because asssuming the device provides it, it seems useless because the driver does not parse the protocol type for each packet and does not use this field. The driver and stack just want to know whether the packet is valid or checksum unneccessary.
Hi Jason and Michael. Are we aligned on this?If yes, I'll write a new version to refresh the thread and try to avoid future rollbacks.
Thanks a lot!
Thanks!If we don't, we need a new flag. ThanksThis publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdfList Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-listsCommittee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/
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