[Qemu-devel] Re: Errors on MMIO read access on VM suspend / resume operations

[Stefan Berger]

On 01/18/2011 03:53 AM, Jan Kiszka wrote:
> On 2011-01-18 04:03, Stefan Berger wrote:
> > On 01/16/2011 09:43 AM, Avi Kivity wrote:
> > > On 01/14/2011 09:27 PM, Stefan Berger wrote:
> > > > > Can you sprinkle some printfs() arount kvm_run (in qemu-kvm.c) to
> > > > > verify this?
> > > > Here's what I did:
> > > >
> > > >
> > > > interrupt exit requested
> > > It appears from this you're using qemu.git.  Please try qemu-kvm.git,
> > > where the code appears to be correct.
> > Cc'ing qemu-devel now. For reference, here the initial problem description:
> >
> > http://www.spinics.net/lists/kvm/msg48274.html
> >
> > I didn't know there was another tree...
> >
> > I have seen now a couple of suspends-while-reading with patches applied
> > to the qemu-kvm.git tree and indeed, when run with the same host kernel
> > and VM I do not see the debugging dumps due to double-reads that I would
> > have anticipated seeing by now. Now what? Can this be easily fixed in
> > the other Qemu tree as well?
> Please give this a try:
>
> git://git.kiszka.org/qemu-kvm.git queues/kvm-upstream
>
> I bet (&  hope) "kvm: Unconditionally reenter kernel after IO exits"
> fixes the issue for you. If other problems pop up with that tree, also
> try resetting to that particular commit.
>
> I'm currently trying to shake all those hidden or forgotten bug fixes
> out of qemu-kvm and port them upstream. Most of those subtle differences
> should hopefully soon be history.
I did the same test as I did with Avi's tree and haven't seen the 
consequences of possible double-reads. So, I would say that you should 
upstream those patches...

I searched for the text you mention above using 'gitk' but couldn't find 
a patch with that headline in your tree. There were others that seem to 
be related:

Gleb Natapov: "do not enter vcpu again if it was stopped during IO"
> > One thing I'd like to mention is that I have seen what I think are
> > interrupt stalls when running my tests inside the qemu-kvm.git tree
> > version and not suspending at all. A some point the interrupt counter in
> > the guest kernel does not increase anymore even though I see the device
> > model raising the IRQ and lowering it. The same tests run literally
> > forever in the qemu.git tree version of Qemu.
> What about qemu-kmv and -no-kvm-irqchip?
That seems to be necessary for both trees, yours and the one Avi pointed 
me to. If applied, then I did not see the interrupt problem.

    Stefan
> Jan