| Message ID | 1398271901-32534-2-git-send-email-vyasevic@redhat.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, Apr 23, 2014 at 12:51:40PM -0400, Vlad Yasevich wrote: > The following is a problematic configuration: > > VM1: virtio-net device connected to macvtap0@eth0 > VM2: e1000 device connect to macvtap1@eth0 > > The problem is is that virtio-net supports checksum offloading > and thus sends the packets to the host with CHECKSUM_PARTIAL set. > On the other hand, e1000 does not support any acceleration. > > For small TCP packets (and this includes the 3-way handshake), > e1000 ends up receiving packets that only have a partial checksum > set. This causes TCP to fail checksum validation and to drop > packets. As a result tcp connections can not be established. > > Commit 3e4f8b787370978733ca6cae452720a4f0c296b8 > macvtap: Perform GSO on forwarding path. > fixes this issue for large packets wthat will end up undergoing GSO. > This commit adds a check for the non-GSO case and attempts to > compute the checksum for partially checksummed packets in the > non-GSO case. > > CC: Daniel Lezcano <daniel.lezcano@free.fr> > CC: Patrick McHardy <kaber@trash.net> > CC: Andrian Nord <nightnord@gmail.com> > CC: Eric Dumazet <eric.dumazet@gmail.com> > CC: Michael S. Tsirkin <mst@redhat.com> > CC: Jason Wang <jasowang@redhat.com> > Signed-off-by: Vlad Yasevich <vyasevic@redhat.com> > --- > drivers/net/macvtap.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > index ff111a8..ba91084 100644 > --- a/drivers/net/macvtap.c > +++ b/drivers/net/macvtap.c > @@ -322,6 +322,13 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb) > segs = nskb; > } > } else { > + /* If we receive a partial checksum and the tap side > + * doesn't support checksum offload, compute the checksum. > + */ > + if (skb->ip_summed == CHECKSUM_PARTIAL && > + !(features & NETIF_F_ALL_CSUM) && > + skb_checksum_help(skb)) > + goto drop; Hmm confused by NETIF_F_ALL_CSUM here. features come from here: feature_mask = NETIF_F_HW_CSUM; if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) { if (arg & TUN_F_TSO_ECN) feature_mask |= NETIF_F_TSO_ECN; if (arg & TUN_F_TSO4) feature_mask |= NETIF_F_TSO; if (arg & TUN_F_TSO6) feature_mask |= NETIF_F_TSO6; } if (arg & TUN_F_UFO) feature_mask |= NETIF_F_UFO; okay so why not just check that NETIF_F_HW_CSUM is set? Also does it matter whether specific offloads are enabled? > skb_queue_tail(&q->sk.sk_receive_queue, skb); > } > > -- > 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 04/23/2014 03:20 PM, Michael S. Tsirkin wrote: > On Wed, Apr 23, 2014 at 12:51:40PM -0400, Vlad Yasevich wrote: >> The following is a problematic configuration: >> >> VM1: virtio-net device connected to macvtap0@eth0 >> VM2: e1000 device connect to macvtap1@eth0 >> >> The problem is is that virtio-net supports checksum offloading >> and thus sends the packets to the host with CHECKSUM_PARTIAL set. >> On the other hand, e1000 does not support any acceleration. >> >> For small TCP packets (and this includes the 3-way handshake), >> e1000 ends up receiving packets that only have a partial checksum >> set. This causes TCP to fail checksum validation and to drop >> packets. As a result tcp connections can not be established. >> >> Commit 3e4f8b787370978733ca6cae452720a4f0c296b8 >> macvtap: Perform GSO on forwarding path. >> fixes this issue for large packets wthat will end up undergoing GSO. >> This commit adds a check for the non-GSO case and attempts to >> compute the checksum for partially checksummed packets in the >> non-GSO case. >> >> CC: Daniel Lezcano <daniel.lezcano@free.fr> >> CC: Patrick McHardy <kaber@trash.net> >> CC: Andrian Nord <nightnord@gmail.com> >> CC: Eric Dumazet <eric.dumazet@gmail.com> >> CC: Michael S. Tsirkin <mst@redhat.com> >> CC: Jason Wang <jasowang@redhat.com> >> Signed-off-by: Vlad Yasevich <vyasevic@redhat.com> >> --- >> drivers/net/macvtap.c | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c >> index ff111a8..ba91084 100644 >> --- a/drivers/net/macvtap.c >> +++ b/drivers/net/macvtap.c >> @@ -322,6 +322,13 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb) >> segs = nskb; >> } >> } else { >> + /* If we receive a partial checksum and the tap side >> + * doesn't support checksum offload, compute the checksum. >> + */ >> + if (skb->ip_summed == CHECKSUM_PARTIAL && >> + !(features & NETIF_F_ALL_CSUM) && >> + skb_checksum_help(skb)) >> + goto drop; > > Hmm confused by NETIF_F_ALL_CSUM here. > > features come from here: > feature_mask = NETIF_F_HW_CSUM; > > if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) { > if (arg & TUN_F_TSO_ECN) > feature_mask |= NETIF_F_TSO_ECN; > if (arg & TUN_F_TSO4) > feature_mask |= NETIF_F_TSO; > if (arg & TUN_F_TSO6) > feature_mask |= NETIF_F_TSO6; > } > > if (arg & TUN_F_UFO) > feature_mask |= NETIF_F_UFO; > > > okay so why not just check that NETIF_F_HW_CSUM is set? We can do that, but it doesn't make much difference. > > Also does it matter whether specific offloads are enabled? > No it doesn't matter at all. The packet is not a GSO packet so no other acceleration is used. Also, other offloads are dependent on checksum. -vlad > >> skb_queue_tail(&q->sk.sk_receive_queue, skb); >> } >> >> -- >> 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Apr 23, 2014 at 03:39:44PM -0400, Vlad Yasevich wrote: > On 04/23/2014 03:20 PM, Michael S. Tsirkin wrote: > > On Wed, Apr 23, 2014 at 12:51:40PM -0400, Vlad Yasevich wrote: > >> The following is a problematic configuration: > >> > >> VM1: virtio-net device connected to macvtap0@eth0 > >> VM2: e1000 device connect to macvtap1@eth0 > >> > >> The problem is is that virtio-net supports checksum offloading > >> and thus sends the packets to the host with CHECKSUM_PARTIAL set. > >> On the other hand, e1000 does not support any acceleration. > >> > >> For small TCP packets (and this includes the 3-way handshake), > >> e1000 ends up receiving packets that only have a partial checksum > >> set. This causes TCP to fail checksum validation and to drop > >> packets. As a result tcp connections can not be established. > >> > >> Commit 3e4f8b787370978733ca6cae452720a4f0c296b8 > >> macvtap: Perform GSO on forwarding path. > >> fixes this issue for large packets wthat will end up undergoing GSO. > >> This commit adds a check for the non-GSO case and attempts to > >> compute the checksum for partially checksummed packets in the > >> non-GSO case. > >> > >> CC: Daniel Lezcano <daniel.lezcano@free.fr> > >> CC: Patrick McHardy <kaber@trash.net> > >> CC: Andrian Nord <nightnord@gmail.com> > >> CC: Eric Dumazet <eric.dumazet@gmail.com> > >> CC: Michael S. Tsirkin <mst@redhat.com> > >> CC: Jason Wang <jasowang@redhat.com> > >> Signed-off-by: Vlad Yasevich <vyasevic@redhat.com> > >> --- > >> drivers/net/macvtap.c | 7 +++++++ > >> 1 file changed, 7 insertions(+) > >> > >> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > >> index ff111a8..ba91084 100644 > >> --- a/drivers/net/macvtap.c > >> +++ b/drivers/net/macvtap.c > >> @@ -322,6 +322,13 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb) > >> segs = nskb; > >> } > >> } else { > >> + /* If we receive a partial checksum and the tap side > >> + * doesn't support checksum offload, compute the checksum. > >> + */ > >> + if (skb->ip_summed == CHECKSUM_PARTIAL && > >> + !(features & NETIF_F_ALL_CSUM) && > >> + skb_checksum_help(skb)) > >> + goto drop; > > > > Hmm confused by NETIF_F_ALL_CSUM here. > > > > features come from here: > > feature_mask = NETIF_F_HW_CSUM; > > > > if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) { > > if (arg & TUN_F_TSO_ECN) > > feature_mask |= NETIF_F_TSO_ECN; > > if (arg & TUN_F_TSO4) > > feature_mask |= NETIF_F_TSO; > > if (arg & TUN_F_TSO6) > > feature_mask |= NETIF_F_TSO6; > > } > > > > if (arg & TUN_F_UFO) > > feature_mask |= NETIF_F_UFO; > > > > > > okay so why not just check that NETIF_F_HW_CSUM is set? > > We can do that, but it doesn't make much difference. Seems cleaner to test a single bit otherwise one is left wondering what happens if only one bit matches. > > > > Also does it matter whether specific offloads are enabled? > > > > No it doesn't matter at all. The packet is not a GSO packet > so no other acceleration is used. Hmm how do we know it's not a gso packet? All I see is need_gso test which means it needs segmentation. > Also, other offloads are dependent on checksum. > > -vlad Right so what if checksum is on, but segmentation is off? Not the case with e1000 today but can be with other userspace. > > > >> skb_queue_tail(&q->sk.sk_receive_queue, skb); > >> } > >> > >> -- > >> 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 04/23/2014 04:10 PM, Michael S. Tsirkin wrote: > On Wed, Apr 23, 2014 at 03:39:44PM -0400, Vlad Yasevich wrote: >> On 04/23/2014 03:20 PM, Michael S. Tsirkin wrote: >>> On Wed, Apr 23, 2014 at 12:51:40PM -0400, Vlad Yasevich wrote: >>>> The following is a problematic configuration: >>>> >>>> VM1: virtio-net device connected to macvtap0@eth0 >>>> VM2: e1000 device connect to macvtap1@eth0 >>>> >>>> The problem is is that virtio-net supports checksum offloading >>>> and thus sends the packets to the host with CHECKSUM_PARTIAL set. >>>> On the other hand, e1000 does not support any acceleration. >>>> >>>> For small TCP packets (and this includes the 3-way handshake), >>>> e1000 ends up receiving packets that only have a partial checksum >>>> set. This causes TCP to fail checksum validation and to drop >>>> packets. As a result tcp connections can not be established. >>>> >>>> Commit 3e4f8b787370978733ca6cae452720a4f0c296b8 >>>> macvtap: Perform GSO on forwarding path. >>>> fixes this issue for large packets wthat will end up undergoing GSO. >>>> This commit adds a check for the non-GSO case and attempts to >>>> compute the checksum for partially checksummed packets in the >>>> non-GSO case. >>>> >>>> CC: Daniel Lezcano <daniel.lezcano@free.fr> >>>> CC: Patrick McHardy <kaber@trash.net> >>>> CC: Andrian Nord <nightnord@gmail.com> >>>> CC: Eric Dumazet <eric.dumazet@gmail.com> >>>> CC: Michael S. Tsirkin <mst@redhat.com> >>>> CC: Jason Wang <jasowang@redhat.com> >>>> Signed-off-by: Vlad Yasevich <vyasevic@redhat.com> >>>> --- >>>> drivers/net/macvtap.c | 7 +++++++ >>>> 1 file changed, 7 insertions(+) >>>> >>>> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c >>>> index ff111a8..ba91084 100644 >>>> --- a/drivers/net/macvtap.c >>>> +++ b/drivers/net/macvtap.c >>>> @@ -322,6 +322,13 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb) >>>> segs = nskb; >>>> } >>>> } else { >>>> + /* If we receive a partial checksum and the tap side >>>> + * doesn't support checksum offload, compute the checksum. >>>> + */ >>>> + if (skb->ip_summed == CHECKSUM_PARTIAL && >>>> + !(features & NETIF_F_ALL_CSUM) && >>>> + skb_checksum_help(skb)) >>>> + goto drop; >>> >>> Hmm confused by NETIF_F_ALL_CSUM here. >>> >>> features come from here: >>> feature_mask = NETIF_F_HW_CSUM; >>> >>> if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) { >>> if (arg & TUN_F_TSO_ECN) >>> feature_mask |= NETIF_F_TSO_ECN; >>> if (arg & TUN_F_TSO4) >>> feature_mask |= NETIF_F_TSO; >>> if (arg & TUN_F_TSO6) >>> feature_mask |= NETIF_F_TSO6; >>> } >>> >>> if (arg & TUN_F_UFO) >>> feature_mask |= NETIF_F_UFO; >>> >>> >>> okay so why not just check that NETIF_F_HW_CSUM is set? >> >> We can do that, but it doesn't make much difference. > > Seems cleaner to test a single bit otherwise one is left > wondering what happens if only one bit matches. I can certainly do a single test, but if we ever change it, this will be another palace that would have to change. The above is also what dev_start_hard_xmit() does. > >>> >>> Also does it matter whether specific offloads are enabled? >>> >> >> No it doesn't matter at all. The packet is not a GSO packet >> so no other acceleration is used. > > Hmm how do we know it's not a gso packet? > All I see is need_gso test which means it needs segmentation. Part of netif_needs_gso() is a test for skb_is_gso(). So it it's gso and doesn't need segmentation (meaning the guest can receive large packets), then partial checksum is OK. > > >> Also, other offloads are dependent on checksum. >> >> -vlad > > Right so what if checksum is on, but segmentation is off? > Not the case with e1000 today but can be with other userspace. > In this case, the skb will be in need to segmentation and will take a different branch. -vlad > >>> >>>> skb_queue_tail(&q->sk.sk_receive_queue, skb); >>>> } >>>> >>>> -- >>>> 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Apr 23, 2014 at 04:30:22PM -0400, Vlad Yasevich wrote: > On 04/23/2014 04:10 PM, Michael S. Tsirkin wrote: > > On Wed, Apr 23, 2014 at 03:39:44PM -0400, Vlad Yasevich wrote: > >> On 04/23/2014 03:20 PM, Michael S. Tsirkin wrote: > >>> On Wed, Apr 23, 2014 at 12:51:40PM -0400, Vlad Yasevich wrote: > >>>> The following is a problematic configuration: > >>>> > >>>> VM1: virtio-net device connected to macvtap0@eth0 > >>>> VM2: e1000 device connect to macvtap1@eth0 > >>>> > >>>> The problem is is that virtio-net supports checksum offloading > >>>> and thus sends the packets to the host with CHECKSUM_PARTIAL set. > >>>> On the other hand, e1000 does not support any acceleration. > >>>> > >>>> For small TCP packets (and this includes the 3-way handshake), > >>>> e1000 ends up receiving packets that only have a partial checksum > >>>> set. This causes TCP to fail checksum validation and to drop > >>>> packets. As a result tcp connections can not be established. > >>>> > >>>> Commit 3e4f8b787370978733ca6cae452720a4f0c296b8 > >>>> macvtap: Perform GSO on forwarding path. > >>>> fixes this issue for large packets wthat will end up undergoing GSO. > >>>> This commit adds a check for the non-GSO case and attempts to > >>>> compute the checksum for partially checksummed packets in the > >>>> non-GSO case. > >>>> > >>>> CC: Daniel Lezcano <daniel.lezcano@free.fr> > >>>> CC: Patrick McHardy <kaber@trash.net> > >>>> CC: Andrian Nord <nightnord@gmail.com> > >>>> CC: Eric Dumazet <eric.dumazet@gmail.com> > >>>> CC: Michael S. Tsirkin <mst@redhat.com> > >>>> CC: Jason Wang <jasowang@redhat.com> > >>>> Signed-off-by: Vlad Yasevich <vyasevic@redhat.com> > >>>> --- > >>>> drivers/net/macvtap.c | 7 +++++++ > >>>> 1 file changed, 7 insertions(+) > >>>> > >>>> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > >>>> index ff111a8..ba91084 100644 > >>>> --- a/drivers/net/macvtap.c > >>>> +++ b/drivers/net/macvtap.c > >>>> @@ -322,6 +322,13 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb) > >>>> segs = nskb; > >>>> } > >>>> } else { > >>>> + /* If we receive a partial checksum and the tap side > >>>> + * doesn't support checksum offload, compute the checksum. > >>>> + */ > >>>> + if (skb->ip_summed == CHECKSUM_PARTIAL && > >>>> + !(features & NETIF_F_ALL_CSUM) && > >>>> + skb_checksum_help(skb)) > >>>> + goto drop; > >>> > >>> Hmm confused by NETIF_F_ALL_CSUM here. > >>> > >>> features come from here: > >>> feature_mask = NETIF_F_HW_CSUM; > >>> > >>> if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) { > >>> if (arg & TUN_F_TSO_ECN) > >>> feature_mask |= NETIF_F_TSO_ECN; > >>> if (arg & TUN_F_TSO4) > >>> feature_mask |= NETIF_F_TSO; > >>> if (arg & TUN_F_TSO6) > >>> feature_mask |= NETIF_F_TSO6; > >>> } > >>> > >>> if (arg & TUN_F_UFO) > >>> feature_mask |= NETIF_F_UFO; > >>> > >>> > >>> okay so why not just check that NETIF_F_HW_CSUM is set? > >> > >> We can do that, but it doesn't make much difference. > > > > Seems cleaner to test a single bit otherwise one is left > > wondering what happens if only one bit matches. > > I can certainly do a single test, but if we ever change it, > this will be another palace that would have to change. Hmm change what exactly? Add support for selectively disabling checksum for specific protocols? > The above is also what dev_start_hard_xmit() does. Yes and I was wondering about that too, but check it out: that one calls: netif_skb_dev_features which in turn calls harmonize_features. And there we have: if (skb->ip_summed != CHECKSUM_NONE && !can_checksum_protocol(features, skb_network_protocol(skb, &tmp))) { features &= ~NETIF_F_ALL_CSUM; } else if (illegal_highdma(dev, skb)) { features &= ~NETIF_F_SG; } So NETIF_F_HW_CSUM is tested because it's cleared by a per-protocol handling here which is not there in your patch. Your patch is still correct - the reason harmonize_features is not necessary is because tap either sets HW_CSUM or nothing, can_checksum_protocol is always true or always false. But since we rely on this anyway, isn't it better to make this explicit? Alternatively let's clarify the comment here: > >>>> + /* If we receive a partial checksum and the tap side > >>>> + * doesn't support checksum offload, compute the checksum. Add: + * Note: it doesn't matter which checksum feature to + * check, we either support them all or none. > >>>> + */ Fine? > > > >>> > >>> Also does it matter whether specific offloads are enabled? > >>> > >> > >> No it doesn't matter at all. The packet is not a GSO packet > >> so no other acceleration is used. > > > > Hmm how do we know it's not a gso packet? > > All I see is need_gso test which means it needs segmentation. > > Part of netif_needs_gso() is a test for skb_is_gso(). So it > it's gso and doesn't need segmentation (meaning the guest can > receive large packets), then partial checksum is OK. That is correct- thanks for the clarification. > > > > > >> Also, other offloads are dependent on checksum. > >> > >> -vlad > > > > Right so what if checksum is on, but segmentation is off? > > Not the case with e1000 today but can be with other userspace. > > > > In this case, the skb will be in need to segmentation and will take > a different branch. > > -vlad > > > >>> > >>>> skb_queue_tail(&q->sk.sk_receive_queue, skb); > >>>> } > >>>> > >>>> -- > >>>> 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 04/24/2014 03:26 AM, Michael S. Tsirkin wrote: > On Wed, Apr 23, 2014 at 04:30:22PM -0400, Vlad Yasevich wrote: >> On 04/23/2014 04:10 PM, Michael S. Tsirkin wrote: >>> On Wed, Apr 23, 2014 at 03:39:44PM -0400, Vlad Yasevich wrote: >>>> On 04/23/2014 03:20 PM, Michael S. Tsirkin wrote: >>>>> On Wed, Apr 23, 2014 at 12:51:40PM -0400, Vlad Yasevich wrote: >>>>>> The following is a problematic configuration: >>>>>> >>>>>> VM1: virtio-net device connected to macvtap0@eth0 >>>>>> VM2: e1000 device connect to macvtap1@eth0 >>>>>> >>>>>> The problem is is that virtio-net supports checksum offloading >>>>>> and thus sends the packets to the host with CHECKSUM_PARTIAL set. >>>>>> On the other hand, e1000 does not support any acceleration. >>>>>> >>>>>> For small TCP packets (and this includes the 3-way handshake), >>>>>> e1000 ends up receiving packets that only have a partial checksum >>>>>> set. This causes TCP to fail checksum validation and to drop >>>>>> packets. As a result tcp connections can not be established. >>>>>> >>>>>> Commit 3e4f8b787370978733ca6cae452720a4f0c296b8 >>>>>> macvtap: Perform GSO on forwarding path. >>>>>> fixes this issue for large packets wthat will end up undergoing GSO. >>>>>> This commit adds a check for the non-GSO case and attempts to >>>>>> compute the checksum for partially checksummed packets in the >>>>>> non-GSO case. >>>>>> >>>>>> CC: Daniel Lezcano <daniel.lezcano@free.fr> >>>>>> CC: Patrick McHardy <kaber@trash.net> >>>>>> CC: Andrian Nord <nightnord@gmail.com> >>>>>> CC: Eric Dumazet <eric.dumazet@gmail.com> >>>>>> CC: Michael S. Tsirkin <mst@redhat.com> >>>>>> CC: Jason Wang <jasowang@redhat.com> >>>>>> Signed-off-by: Vlad Yasevich <vyasevic@redhat.com> >>>>>> --- >>>>>> drivers/net/macvtap.c | 7 +++++++ >>>>>> 1 file changed, 7 insertions(+) >>>>>> >>>>>> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c >>>>>> index ff111a8..ba91084 100644 >>>>>> --- a/drivers/net/macvtap.c >>>>>> +++ b/drivers/net/macvtap.c >>>>>> @@ -322,6 +322,13 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb) >>>>>> segs = nskb; >>>>>> } >>>>>> } else { >>>>>> + /* If we receive a partial checksum and the tap side >>>>>> + * doesn't support checksum offload, compute the checksum. >>>>>> + */ >>>>>> + if (skb->ip_summed == CHECKSUM_PARTIAL && >>>>>> + !(features & NETIF_F_ALL_CSUM) && >>>>>> + skb_checksum_help(skb)) >>>>>> + goto drop; >>>>> >>>>> Hmm confused by NETIF_F_ALL_CSUM here. >>>>> >>>>> features come from here: >>>>> feature_mask = NETIF_F_HW_CSUM; >>>>> >>>>> if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) { >>>>> if (arg & TUN_F_TSO_ECN) >>>>> feature_mask |= NETIF_F_TSO_ECN; >>>>> if (arg & TUN_F_TSO4) >>>>> feature_mask |= NETIF_F_TSO; >>>>> if (arg & TUN_F_TSO6) >>>>> feature_mask |= NETIF_F_TSO6; >>>>> } >>>>> >>>>> if (arg & TUN_F_UFO) >>>>> feature_mask |= NETIF_F_UFO; >>>>> >>>>> >>>>> okay so why not just check that NETIF_F_HW_CSUM is set? >>>> >>>> We can do that, but it doesn't make much difference. >>> >>> Seems cleaner to test a single bit otherwise one is left >>> wondering what happens if only one bit matches. >> >> I can certainly do a single test, but if we ever change it, >> this will be another palace that would have to change. > > Hmm change what exactly? Add support for selectively > disabling checksum for specific protocols? Yes. Right now, we kind-of lump them all together, but there are some protocols that are not accounted for in HW_CSUM. For instance, I am looking to add SCTP checksum offload. It would be very useful if the host has SCTP-capable nic. > >> The above is also what dev_start_hard_xmit() does. > > Yes and I was wondering about that too, but check it out: that one > calls: netif_skb_dev_features which in turn calls harmonize_features. > And there we have: > if (skb->ip_summed != CHECKSUM_NONE && > !can_checksum_protocol(features, skb_network_protocol(skb, &tmp))) { > features &= ~NETIF_F_ALL_CSUM; > } else if (illegal_highdma(dev, skb)) { > features &= ~NETIF_F_SG; > } > > So NETIF_F_HW_CSUM is tested because it's cleared by a per-protocol > handling here which is not there in your patch. > > Your patch is still correct - the reason harmonize_features is not > necessary is because tap either sets HW_CSUM or nothing, > can_checksum_protocol is always true or always false. But since we rely > on this anyway, isn't it better to make this explicit? > > Alternatively let's clarify the comment here: > >>>>>> + /* If we receive a partial checksum and the tap side >>>>>> + * doesn't support checksum offload, compute the checksum. > > Add: > > + * Note: it doesn't matter which checksum feature to > + * check, we either support them all or none. > >>>>>> + */ > > Fine? Looks good to me. I'll update and re-submit. Thanks -vlad > >>> >>>>> >>>>> Also does it matter whether specific offloads are enabled? >>>>> >>>> >>>> No it doesn't matter at all. The packet is not a GSO packet >>>> so no other acceleration is used. >>> >>> Hmm how do we know it's not a gso packet? >>> All I see is need_gso test which means it needs segmentation. >> >> Part of netif_needs_gso() is a test for skb_is_gso(). So it >> it's gso and doesn't need segmentation (meaning the guest can >> receive large packets), then partial checksum is OK. > > That is correct- thanks for the clarification. > > >>> >>> >>>> Also, other offloads are dependent on checksum. >>>> >>>> -vlad >>> >>> Right so what if checksum is on, but segmentation is off? >>> Not the case with e1000 today but can be with other userspace. >>> >> >> In this case, the skb will be in need to segmentation and will take >> a different branch. >> >> -vlad >>> >>>>> >>>>>> skb_queue_tail(&q->sk.sk_receive_queue, skb); >>>>>> } >>>>>> >>>>>> -- >>>>>> 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c index ff111a8..ba91084 100644 --- a/drivers/net/macvtap.c +++ b/drivers/net/macvtap.c @@ -322,6 +322,13 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb) segs = nskb; } } else { + /* If we receive a partial checksum and the tap side + * doesn't support checksum offload, compute the checksum. + */ + if (skb->ip_summed == CHECKSUM_PARTIAL && + !(features & NETIF_F_ALL_CSUM) && + skb_checksum_help(skb)) + goto drop; skb_queue_tail(&q->sk.sk_receive_queue, skb); }
The following is a problematic configuration: VM1: virtio-net device connected to macvtap0@eth0 VM2: e1000 device connect to macvtap1@eth0 The problem is is that virtio-net supports checksum offloading and thus sends the packets to the host with CHECKSUM_PARTIAL set. On the other hand, e1000 does not support any acceleration. For small TCP packets (and this includes the 3-way handshake), e1000 ends up receiving packets that only have a partial checksum set. This causes TCP to fail checksum validation and to drop packets. As a result tcp connections can not be established. Commit 3e4f8b787370978733ca6cae452720a4f0c296b8 macvtap: Perform GSO on forwarding path. fixes this issue for large packets wthat will end up undergoing GSO. This commit adds a check for the non-GSO case and attempts to compute the checksum for partially checksummed packets in the non-GSO case. CC: Daniel Lezcano <daniel.lezcano@free.fr> CC: Patrick McHardy <kaber@trash.net> CC: Andrian Nord <nightnord@gmail.com> CC: Eric Dumazet <eric.dumazet@gmail.com> CC: Michael S. Tsirkin <mst@redhat.com> CC: Jason Wang <jasowang@redhat.com> Signed-off-by: Vlad Yasevich <vyasevic@redhat.com> --- drivers/net/macvtap.c | 7 +++++++ 1 file changed, 7 insertions(+)