netdev - Re: [PATCH net-next] xen-netfront: try linearizing SKB if it occupies too many slots

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Message-ID: <1400245474.7973.154.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 16 May 2014 06:04:34 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Wei Liu <wei.liu2@...rix.com>
Cc:	netdev@...r.kernel.org, xen-devel@...ts.xen.org,
	David Vrabel <david.vrabel@...rix.com>,
	Konrad Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Stefan Bader <stefan.bader@...onical.com>,
	Zoltan Kiss <zoltan.kiss@...rix.com>
Subject: Re: [PATCH net-next] xen-netfront: try linearizing SKB if it
 occupies too many slots

On Fri, 2014-05-16 at 12:08 +0100, Wei Liu wrote:
> Some workload, such as Redis can generate SKBs which make use of
> compound pages. Netfront doesn't quite like that because it doesn't want
> to send packet that occupies exessive slots to the backend as backend
> might deem it malicious. On the flip side these packets are actually
> legit, the size check at the beginning of xennet_start_xmit ensures that
> packet size is below 64K.
> 
> So we linearize SKB if it occupies too many slots. If the linearization
> fails then the SKB is dropped.
> 
> Signed-off-by: Wei Liu <wei.liu2@...rix.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> Cc: Konrad Wilk <konrad.wilk@...cle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Stefan Bader <stefan.bader@...onical.com>
> Cc: Zoltan Kiss <zoltan.kiss@...rix.com>
> ---
>  drivers/net/xen-netfront.c |   17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)

This is likely to fail on typical host.

What about adding a smart helper trying to aggregate consecutive
smallest fragments into a single frag ?

This would be needed for bnx2x for example as well.


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