On Thu, Dec 20, 2012 at 08:42:06AM +0200, Gleb Natapov wrote: > 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 <yang.z.zhang@xxxxxxxxx> > > > > > > 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 <kevin.tian@xxxxxxxxx> > > > Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx> > > > > > > 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. Its just confusing, to have a variable which has different meanings in different configurations. I would rather have it explicit that its not used rather than check every time the i read the code. if (apic_vid() == 0 && !apic->irr_pending) return -1; > > 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. Not sure if you can skip it, its probably necessary to calculate it before HW does so (say migration etc). -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
