linux-kernel - Re: [PATCH net 1/2] virtio-net: disable guest csum during XDP set

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Date:   Fri, 23 Nov 2018 12:01:19 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     jasowang@...hat.com
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        brouer@...hat.com, pashinho1990@...il.com, dsahern@...il.com
Subject: Re: [PATCH net 1/2] virtio-net: disable guest csum during XDP set

From: Jason Wang <jasowang@...hat.com>
Date: Thu, 22 Nov 2018 14:36:30 +0800

> We don't disable VIRTIO_NET_F_GUEST_CSUM if XDP was set. This means we
> can receive partial csumed packets with metadata kept in the
> vnet_hdr. This may have several side effects:
> 
> - It could be overridden by header adjustment, thus is might be not
>   correct after XDP processing.
> - There's no way to pass such metadata information through
>   XDP_REDIRECT to another driver.
> - XDP does not support checksum offload right now.
> 
> So simply disable guest csum if possible in this the case of XDP.
> 
> Fixes: 3f93522ffab2d ("virtio-net: switch off offloads on demand if possible on XDP set")
> Reported-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Cc: Jesper Dangaard Brouer <brouer@...hat.com>
> Cc: Pavel Popa <pashinho1990@...il.com>
> Cc: David Ahern <dsahern@...il.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Applied and queued up for -stable.

We really should have a way to use the checksum provided if the XDP
program returns XDP_PASS and does not modify the packet contents
or size.