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

[Marcelo Tosatti <mtosatti@redhat.com>]

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/kvm@vger.kernel.org/msg41681.html

tpr of a vcpu should always be inspected in vcpu context, instead of 
iothread context?