On Wed, Dec 19, 2012 at 10:59:36PM -0200, Marcelo Tosatti wrote:
> On Mon, Dec 17, 2012 at 01:30:49PM +0800, Yang Zhang wrote:
> > From: Yang Zhang <[email protected]>
> >
> > Virtual interrupt delivery avoids KVM to inject vAPIC interrupts
> > manually, which is fully taken care of by the hardware. This needs
> > some special awareness into existing interrupr injection path:
> >
> > - for pending interrupt, instead of direct injection, we may need
> > update architecture specific indicators before resuming to guest.
> >
> > - A pending interrupt, which is masked by ISR, should be also
> > considered in above update action, since hardware will decide
> > when to inject it at right time. Current has_interrupt and
> > get_interrupt only returns a valid vector from injection p.o.v.
> >
> > Signed-off-by: Kevin Tian <[email protected]>
> > Signed-off-by: Yang Zhang <[email protected]>
>
>
> Resuming previous discussion:
>
> > > How about to recaculate irr_pending according the VIRR on each
> > > vmexit?
> > >
> > No need really. Since HW can only clear VIRR the only situation that
> > may
> > happen is that irr_pending will be true but VIRR is empty and
> > apic_find_highest_irr() will return correct result in this case.
>
> Self-IPI does cause VIRR to be set, see "29.1.5 Self-IPI
> Virtualization".
>
True. But as I said later in that discussion once irr_pending is set
to true it never becomes false, so the optimization is effectively
disable. We can set it to true doing apic initialization to make it
explicit.
> Also, an example of problem with ISR caching optimization (which was written
> with ISR/IRR management entirely in software):
>
> isr_count variable is never incremented (because HW sets ISR):
> kvm_cpu_get_interrupt does not call into kvm_get_apic_interrupt
> if virtual interrupt delivery enabled.
>
> Therefore apic_find_highest_isr can return -1 even though VISR
> is not zero.
>
> In that case (VISR non-zero but apic_find_highest_isr() == -1),
> apic_update_ppr does not correctly set
>
> PPR = max(ISRV, TPR)
>
> Which can result in kvm_arch_vcpu_runnable returning 1 when it should not.
>
> Please disable usage of isr_count if virtual interrupt delivery enabled.
> Given that self-IPI writes to VIRR, also please disable usage of
> highest_isr_cache and irr_pending.
>
Good catch about isr_count. We can set it to 1 during apic
initialization too, or skip call to apic_update_ppr() in
kvm_apic_has_interrupt() if vid is enabled.
--
Gleb.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
