On 2011-02-03 11:01, Avi Kivity wrote: > On 02/03/2011 11:32 AM, 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. > > I don't see why there should be any spurious interrupts in normal > operation. From the docs, these happen due to an INTA cycle racing with > raising the TPR, but in ioapic mode, there shouldn't be any INTA cycles. >
I added an instrumentation to the line of apic_get_interrupt that returns the spurious vector, and it triggered fairly often. Just didn't examined why this happens even without the tpr optimization. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
