netdev - Re: [PATCH 5/5] skbuff: skb_segment: orphan frags before copying

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Message-ID: <20140310213404.GB15352@gondor.apana.org.au>
Date:	Tue, 11 Mar 2014 05:34:05 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org, jbenc@...hat.com,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Simon Horman <horms@...ge.net.au>,
	Paul Durrant <Paul.Durrant@...rix.com>,
	Thomas Graf <tgraf@...g.ch>, Miklos Szeredi <mszeredi@...e.cz>,
	=?UTF-8?q?Peter=20Pan=28=E6=BD=98=E5=8D=AB=E5=B9=B3=29?= <panweiping3@...il.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH 5/5] skbuff: skb_segment: orphan frags before copying

On Mon, Mar 10, 2014 at 06:29:36PM +0200, Michael S. Tsirkin wrote:
> skb_segment copies frags around, so we need
> to copy them carefully to avoid accessing
> user memory after reporting completion to userspace
> through a callback.
> 
> skb_segment doesn't normally happen on datapath:
> TSO needs to be disabled - so disabling zero copy
> in this case does not look like a big deal.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

Why do we need this patch at all? Contrary to what you said,
this path is definitely performance-critical since the basis
of being able to enable GSO by default is that it causes no
regressions in non-TSO cases.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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