Subject: Re: kvm causing memory corruption?  now 2.6.26-rc4
From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Avi Kivity <avi@qumranet.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "Anthony N. Liguori [imap]" <aliguori@us.ibm.com>, kvm@vger.kernel.org
In-Reply-To: <1212445810.8211.9.camel@nimitz.home.sr71.net>
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	 <1206629709.7883.30.camel@nimitz.home.sr71.net>
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Date: Mon, 02 Jun 2008 17:59:58 -0700
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On Mon, 2008-06-02 at 15:30 -0700, Dave Hansen wrote:
> On Thu, 2008-03-27 at 16:59 +0200, Avi Kivity wrote:
> > Dave Hansen wrote:
> > > On Thu, 2008-03-27 at 12:10 +0200, Avi Kivity wrote:
> > >> btw, is this with >= 4GB RAM on the host?
> > >
> > > Well, are you asking whether I have PAE on or not? :)  
> > 
> > No, I'm asking whether there is a possibility of address truncation :)
> > 
> > PAE by itself doesn't affect kvm much, as it always runs the guest in 
> > pae mode.
> > 
> > Can you try running with mem=2000M or something?
> 
> I have a few more data points on this.  Sorry for the massive delay from
> the last report -- I'm being a crappy bug reporter.  But, this is on my
> one and only laptop which makes it a serious pain to diagnose.  I also
> didn't have a hardware serial console on it before, which I do now.
> This is all on 2.6.26-rc4-01549-g1beee8d.
> 
> Adding the mem= does not help at all.  But, it is all a bit more
> diagnosable now than a month or two ago.  I turned on all of the kernel
> debugging that I could get my grubby little hands on.  It now oopses
> quite consistently when kvm runs instead of after.  Here's a collection
> of oopses that I captured after setting up a serial line:
> 
> 	http://sr71.net/~dave/kvm-oops1.txt
> 
> After collecting all those, I turned on CONFIG_DEBUG_HIGHMEM and the
> oopses miraculously stopped.  But, the guest hung (for at least 5
> minutes or so) during windows bootup, pegging my host CPU.  Most of the
> CPU was going to klogd, so I checked dmesg.
> 
> I was seeing messages like this
> 
> [  428.918108] kvm_handle_exit: unexpected, valid vectoring info and exit reason is 0x9
> 
> And quite a few of them, like 100,000/sec.  That's why klogd was pegging
> the CPU.  Any idea on a next debugging step?

I followed these steps, and can now boot a vm.  But, causing the host
crashes is still a pretty bad bug.  I would imagine turning ACPI back on
will let me reproduce if necessary.

http://kvm.qumranet.com/kvmwiki/Windows_ACPI_Workaround

-- Dave

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