netdev - Re: [PATCH 2/2] vhost_net: a kernel-level virtio server

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Message-Id: <200908201655.48779.rusty@rustcorp.com.au>
Date:	Thu, 20 Aug 2009 16:55:48 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	virtualization@...ts.linux-foundation.org
Cc:	Arnd Bergmann <arnd@...db.de>,
	"Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
	"Ira W. Snyder" <iws@...o.caltech.edu>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 2/2] vhost_net: a kernel-level virtio server

On Fri, 14 Aug 2009 12:23:46 am Arnd Bergmann wrote:
> On Thursday 13 August 2009, Michael S. Tsirkin wrote:
> > The best way to do this IMO would be to add zero copy support to raw
> > sockets, vhost will then get it basically for free.
> 
> Yes, that would be nice. I wonder if that could lead to security
> problems on TX though. I guess It will only bring significant performance
> improvements if we leave the data writable in the user space or guest
> during the operation. If the user finds the right timing, it could
> modify the frame headers after they have been checked using netfilter,
> or while the frames are being consumed in the kernel (e.g. an NFS
> server running in a guest).

For this reason, we always linearize parts of packets we're filtering.
ie. copy.

Cheers,
Rusty.
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