Re: kvm causing memory corruption? now 2.6.26-rc4

Avi Kivity
2008-06-04T13:42:48Z

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.
>
>

Can you check with mem=900 (and CONFIG_HIGHMEM_DEBUG=n)? That will
confirm that the problems are highmem related, but not physical address
truncation related.

> 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?
>
>

That's a task switch. Newer kvms handle them.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.