linux-kernel - Re: kvm causing memory corruption? now 2.6.26-rc4

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Message-Id: <1212445810.8211.9.camel@nimitz.home.sr71.net>
Date:	Mon, 02 Jun 2008 15:30:10 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...ranet.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	"Anthony N. Liguori [imap]" <aliguori@...ibm.com>
Subject: Re: kvm causing memory corruption?  now 2.6.26-rc4

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?

-- Dave

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