Re: [Qemu-devel] KVM: Windows 64-bit troubles with user space irqchip

[Gleb Natapov]

On Thu, Feb 03, 2011 at 11:11:23AM +0100, Jan Kiszka wrote:
> On 2011-02-03 11:04, Marcelo Tosatti wrote:
> > On Thu, Feb 03, 2011 at 10:32:25AM +0100, Jan Kiszka wrote:
> >> On 2011-02-03 09:18, Avi Kivity wrote:
> >>> On 02/02/2011 05:52 PM, Jan Kiszka wrote:
> >>>>>>
> >>>>>  If there is no problem in the logic of this commit (and I do not see
> >>>>>  one yet) then we somewhere miss kicking vcpu when interrupt, that 
> >>>>> should be
> >>>>>  handled, arrives?
> >>>>
> >>>> I'm not yet confident about the logic of the kernel patch: mov to cr8 is
> >>>> serializing. If the guest raises the tpr and then signals this with a
> >>>> succeeding, non vm-exiting instruction to the other vcpus, one of those
> >>>> could inject an interrupt with a higher priority than the previous tpr,
> >>>> but a lower one than current tpr. QEMU user space would accept this
> >>>> interrupt - and would likely surprise the guest. Do I miss something?
> >>>
> >>> apic_get_interrupt() is only called from the vcpu thread, so it should 
> >>> see a correct tpr.
> >>>
> >>> The only difference I can see with the patch is that we may issue a 
> >>> spurious cpu_interrupt().  But that shouldn't do anything bad, should it?
> >>
> >> I tested this yesterday, and it doesn't confuse Windows. It actually
> >> receives quite a few spurious IRQs in normal operation, w/ or w/o the
> >> kernel's tpr optimization.
> > 
> > http://www.mail-archive.com/address@hidden/msg41681.html
> 
> Don't get the scenario yet: We do not inject (or set isr) over the
> context of apic_set_irq caller.
> 
> > 
> > tpr of a vcpu should always be inspected in vcpu context, instead of 
> > iothread context?
> 
> Maybe this is true for the in-kernel model, but I don't see the issue
> (anymore) for the way user space works.
> 
With patch below I can boot Windows7.

diff --git a/hw/apic.c b/hw/apic.c
index 146deca..fdcac88 100644
--- a/hw/apic.c
+++ b/hw/apic.c
@@ -600,7 +600,7 @@ int apic_get_interrupt(DeviceState *d)
     intno = get_highest_priority_int(s->irr);
     if (intno < 0)
         return -1;
-    if (s->tpr && intno <= s->tpr)
+    if ((s->tpr >> 4) && (intno >> 4) <= (s->tpr >> 4))
         return s->spurious_vec & 0xff;
     reset_bit(s->irr, intno);
     set_bit(s->isr, intno);
--
                        Gleb.