From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 26 Feb 2020 04:33:30 -0500

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Subject: Re: virtio_net: can change MTU after installing program
Message-ID: <[email-masked]>
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In-Reply-To: <[email-masked]>

On Tue, Feb 25, 2020 at 08:32:14PM -0700, David Ahern wrote:
> Another issue is that virtio_net checks the MTU when a program is
> installed, but does not restrict an MTU change after:
> 
> # ip li sh dev eth0
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdp qdisc fq_codel
> state UP mode DEFAULT group default qlen 1000
>     link/ether 5a:39:e6:01:a5:36 brd ff:ff:ff:ff:ff:ff
>     prog/xdp id 13 tag c5595e4590d58063 jited
> 
> # ip li set dev eth0 mtu 8192
> 
> # ip li sh dev eth0
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 8192 xdp qdisc fq_codel
> state UP mode DEFAULT group default qlen 1000
> 
> 

Cc Toke who has tested this on other cards and has some input.

-- 
MST