netdev - Re: [PATCH net] net: thunderx: don't allow jumbo frames with XDP

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Message-Id: <20190404.172039.1083206882112207747.davem@davemloft.net>
Date:   Thu, 04 Apr 2019 17:20:39 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     mcroce@...hat.com
Cc:     netdev@...r.kernel.org, sgoutham@...ium.com, rric@...nel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net] net: thunderx: don't allow jumbo frames with XDP

From: Matteo Croce <mcroce@...hat.com>
Date: Wed,  3 Apr 2019 01:11:36 +0200

> The thunderx driver forbids to load an eBPF program if the MTU is higher
> than 1500 bytes, but this can be circumvented by first loading the eBPF,
> and then raising the MTU.
> 
> XDP assumes that SKBs are linear and fit in a single page, this can lead
> to undefined behaviours.
> Fix this by limiting the MTU to 1500 bytes if an eBPF program is loaded.
> 
> Fixes: 05c773f52b96e ("net: thunderx: Add basic XDP support")
> Signed-off-by: Matteo Croce <mcroce@...hat.com>

Please respond to Jesper's feedback about your choice of a limit of 1500.

Otherwise I will toss your patch.