linux-kernel - Re: KVM induced panic on 2.6.38[2367] & 2.6.39

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Date:	Mon, 22 Aug 2011 08:45:03 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Brad Campbell <lists2009@...rfbargle.com>, CaT <cat@....com.au>,
	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: KVM induced panic on 2.6.38[2367] & 2.6.39

Le lundi 22 août 2011 à 09:36 +0300, Avi Kivity a écrit :
> On 08/20/2011 04:16 PM, Brad Campbell wrote:
> > Author: Alexander Duyck <alexander.h.duyck@...el.com>
> > Date:   Thu Jul 1 13:28:27 2010 +0000
> >
> >     x86: Drop CONFIG_MCORE2 check around setting of NET_IP_ALIGN
> >
> >     This patch removes the CONFIG_MCORE2 check from around 
> > NET_IP_ALIGN.  It is
> >     based on a suggestion from Andi Kleen.  The assumption is that 
> > there are
> >     not any x86 cores where unaligned access is really slow, and this 
> > change
> >     would allow for a performance improvement to still exist on 
> > configurations
> >     that are not necessarily optimized for Core 2.
> >
> >     Cc: Andi Kleen <ak@...ux.intel.com>
> >     Cc: Thomas Gleixner <tglx@...utronix.de>
> >     Cc: Ingo Molnar <mingo@...hat.com>
> >     Cc: "H. Peter Anvin" <hpa@...or.com>
> >     Cc: x86@...nel.org
> >     Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
> >     Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> >     Acked-by: H. Peter Anvin <hpa@...or.com>
> >     Signed-off-by: David S. Miller <davem@...emloft.net>
> >
> > :040000 040000 5a15867789080a2f67a74b17c4422f85b7a9fb4a 
> > b98769348bd765731ca3ff03b33764257e23226c M    arch
> >
> > I can confirm this bug exists in the 3.0 kernel, however I'm unable to 
> > reproduce it on todays git.
> >
> > So anyone using netfilter, kvm and bridge on kernels between 
> > 2.6.36-rc1 and 3.0 may hit this bug, but it looks like it is fixed in 
> > the current 3.1-rc kernels.
> >
> 
> Thanks for this effort.  I don't think this patch is buggy in itself, it 
> merely exposed another bug which was fixed later on.
> 

Some piece of hardware has a 2-byte offset requirement, and driver
incorrectly assumed NET_IP_ALIGN was 2 on x86.

Brad, could you post your config (lsmod, dmesg) again ?

tg3.c code for example uses a private value, not related to NET_IP_ALIGN

#define TG3_RAW_IP_ALIGN 2



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