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From: Rusty Russell <rusty@rustcorp.com.au>
To: virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 2/2] vhost_net: a kernel-level virtio server
Date: Thu, 20 Aug 2009 16:55:48 +0930
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Cc: Arnd Bergmann <arnd@arndb.de>, "Michael S. Tsirkin" <mst@redhat.com>,
       netdev@vger.kernel.org, "Ira W. Snyder" <iws@ovro.caltech.edu>,
       linux-kernel@vger.kernel.org, kvm@vger.kernel.org
References: <cover.1249930169.git.mst@redhat.com> <20090813144129.GB5080@redhat.com> <200908131653.47029.arnd@arndb.de>
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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.