linux-kernel - Re: percpu crash on NetBurst

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Date:	Wed, 21 Sep 2011 17:28:07 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Tejun Heo <tj@...nel.org>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: percpu crash on NetBurst

On 08/08/2011 12:55 PM, Tejun Heo wrote:
> Hello, Avi.
>
> On Sun, Aug 07, 2011 at 06:32:35PM +0300, Avi Kivity wrote:
> >  qemu, under some conditions (-cpu host or -cpu kvm64), erroneously
> >  passes family=15 as the virtual cpuid.  This causes a BUG() in
> >  percpu code during late boot:
> >
> >  ------------[ cut here ]------------
> >  kernel BUG at mm/percpu.c:577!
>

<snip>

> >  All this applies to v3.0; current upstream (c2f340a69ca) fails even
> >  worse, haven't yet determined exactly why.
> >
> >  I'm surprised this hasn't been reported before; Ingo, don't you have
> >  family=15 hosts in your test farm?
>
> Hmmm... I can't trigger the problem w/ kvm64 (I tried mounting and
> unmounting filesystems but it worked okay) and am quite skeptical this
> is a wide spread problem given that the percpu core code is used very
> widely and hasn't seen a lot of changes lately.  Is there anything
> specific you need to do to trigger the condition?  Can you try to
> print out the s_files addresses being allocated and freed?
>

Coming back to this, the trigger if cpuid family=6 and model>=13 (model 
12 works).  Looks like the code disables rep_good is some MSR doesn't 
have the expected value.  While we should configure the MSR correctly, 
it looks like the fallback code for !rep_good is broken.  Will look further.

-- 
error compiling committee.c: too many arguments to function

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