netdev - Re: [net PATCH 1/2] virtio_net: cap mtu when XDP programs are running

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Message-ID: <9aa07031-8c09-dbeb-c7ed-41daf5866be2@redhat.com>
Date:   Thu, 5 Jan 2017 17:34:05 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     john.r.fastabend@...el.com, netdev@...r.kernel.org
Subject: Re: [net PATCH 1/2] virtio_net: cap mtu when XDP programs are running



On 2017年01月05日 11:18, Michael S. Tsirkin wrote:
> On Wed, Jan 04, 2017 at 07:11:18PM -0800, John Fastabend wrote:
>> XDP programs can not consume multiple pages so we cap the MTU to
>> avoid this case. Virtio-net however only checks the MTU at XDP
>> program load and does not block MTU changes after the program
>> has loaded.
> Do drivers really have to tweak max mtu all the time?
> Seems strange, I would say drivers just report device caps
> and net core enforces rules.
> Can't net core do these checks?

I think this needs host co-operation, at least this patch prevents user 
from misconfiguring mtu in guest.