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Message-ID: <20200226093330.GA711395@redhat.com>
Date:   Wed, 26 Feb 2020 04:33:30 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     David Ahern <dahern@...italocean.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>

Bcc: 
Subject: Re: virtio_net: can change MTU after installing program
Message-ID: <20200226043257-mutt-send-email-mst@...nel.org>
Reply-To: 
In-Reply-To: <7df5bb7f-ea69-7673-642b-f174e45a1e64@...italocean.com>

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