From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: [PATCH net 1/3] vlan: Fix tcp checksums offloads for Q-in-Q vlan. Date: Fri, 19 May 2017 05:53:19 -0400 Message-ID: <1eeb2dc0-5877-0834-76af-677f6ca6b5d9@redhat.com> References: <1495114265-23368-1-git-send-email-vyasevic@redhat.com> <1495114265-23368-2-git-send-email-vyasevic@redhat.com> <7593b180-9355-2c14-6cd8-b1e4f47a0ae6@lab.ntt.co.jp> <95de0652-6d73-9885-875e-8c98d02bd419@redhat.com> Reply-To: vyasevic@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: mkubecek@suse.cz To: Toshiaki Makita , Vladislav Yasevich , netdev@vger.kernel.org Return-path: Received: from mx1.redhat.com ([209.132.183.28]:54006 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751861AbdESJxV (ORCPT ); Fri, 19 May 2017 05:53:21 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 05/19/2017 04:16 AM, Toshiaki Makita wrote: > On 2017/05/19 16:09, Vlad Yasevich wrote: >> On 05/18/2017 10:13 PM, Toshiaki Makita wrote: >>> On 2017/05/18 22:31, Vladislav Yasevich wrote: >>>> It appears that since commit 8cb65d000, Q-in-Q vlans have been >>>> broken. The series that commit is part of enabled TSO and checksum >>>> offloading on Q-in-Q vlans. However, most HW we support can't handle >>>> it. To work around the issue, the above commit added a function that >>>> turns off offloads on Q-in-Q devices, but it left the checksum offload. >>>> That will cause issues with most older devices that supprort very basic >>>> checksum offload capabilities as well as some newer devices (we've >>>> reproduced te problem with both be2net and bnx). >>>> >>>> To solve this for everyone, turn off checksum offloading feature >>>> by default when sending Q-in-Q traffic. Devices that are proven to >>>> work can provided a corrected ndo_features_check implemetation. >>>> >>>> Fixes: 8cb65d000 ("net: Move check for multiple vlans to drivers") >>>> CC: Toshiaki Makita >>>> Signed-off-by: Vladislav Yasevich >>>> --- >>>> include/linux/if_vlan.h | 1 - >>>> 1 file changed, 1 deletion(-) >>>> >>>> diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h >>>> index 8d5fcd6..ae537f0 100644 >>>> --- a/include/linux/if_vlan.h >>>> +++ b/include/linux/if_vlan.h >>>> @@ -619,7 +619,6 @@ static inline netdev_features_t vlan_features_check(const struct sk_buff *skb, >>>> NETIF_F_SG | >>>> NETIF_F_HIGHDMA | >>>> NETIF_F_FRAGLIST | >>>> - NETIF_F_HW_CSUM | >>>> NETIF_F_HW_VLAN_CTAG_TX | >>>> NETIF_F_HW_VLAN_STAG_TX); >>>> >>> >>> I guess HW_CSUM theoretically can handle Q-in-Q packets and the problem >>> is IP_CSUM and IPV6_CSUM. >>> So wouldn't it be better to leave HW_CSUM and drop IP_CSUM/IPV6_CSUM, >>> i.e. change intersection into bitwise AND? >>> >> >> It wasn't really a problem before accelerations got enabled on q-in-q >> vlans. > > Right for stacked vlan device. > But I think the check was there for packets from guests forwarded by > bridge to vlan device so it was a problem before 8cb65d000. Not really, since stacked vlans in guests wouldn't have accelerations on. Haven't really tried a new guest on old hosts. It might be an issue there... > >>> The intersection was introduced in db115037bb57 ("net: fix checksum >>> features handling in netif_skb_features()"), but I guess for this >>> particular check the intersection was not needed. >>> >> >> So, to put it another way, leave the intersection with HW_CSUM in the mask, >> and then do: >> >> return features & ~(NETIF_F_IP_CSUM|NETIF_F_IPV6_CSUM); >> >> This might work, but it assumes that everyone who announce HW_CSUM can >> do q-in-q vlans. It's been a bit of a pain tracking this down and I'd rather >> fix it for everyone and let individual driver authors verify that Q-in-Q works >> correctly with HW checksum. However, I am willing to do the above if >> that's what people want. > > At least HW_CSUM in the check was introduced intentionally. > https://www.spinics.net/lists/netdev/msg152016.html > > And I think HW_CSUM should work with any packets. > You know, include/linux/skbuff.h says >> * NETIF_F_HW_CSUM - The driver (or its device) is able to compute one >> * IP (one's complement) checksum for any combination >> * of protocols or protocol layering. > > We should be able to safely enable it. > > ...But you are so worried about layer2 protocol handling of HW_CSUM > devices, I'm ok with disabling it for now. > It's a concern after running across this issue. Granted, the few devices we've seen this bug on use IP/IPV6 checksum features. I am hoping someone else might weigh in here. -vlad