Avi Kivity wrote:
Jan Kiszka wrote:
Jiajun kindly provided me a RHEL kernel and initrd (2.6.18-53-el5) which
I ran for a while (or booted a few times) to trigger the hang. Basically
you need high IRQ load (preferably via LAPIC, to exploit that un-acked
IRQs will block low-prio IRQs as well) + high NMI load (e.g. via NMI
watchdog).
I was able to reproduce it easily by zapping the mmu every second.
Attached is a patch the fixes it for me. Basically it avoids the nmi
path if an interrupt is being injected. This is closer to my event
queue plan, and also is similar to what the code does today with
exceptions (avoid ->inject_pending_irq() if an exception is pending).
Oh, and I think this is more correct than the previous approach of
letting the nmi preempt the interrupt.
The nmi handler could change the tpr to mask the preempted interrupt;
but the code would not notice that. Once the interrupt was injected the
guest would see an interrupt at a higher priority than it has programmed
the hardware to allow.
Basically, once we commit to an interrupt via kvm_cpu_get_interrupt(),
we must inject it before the any instruction gets executed.
I don't think any real guest would notice, though.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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