On 2011-05-03 11:43, Avi Kivity wrote:
> On 04/24/2011 05:08 PM, Jan Kiszka wrote:
>> On 2011-04-24 08:44, Avi Kivity wrote:
>> > On 04/24/2011 01:50 AM, OGAWA Hirofumi wrote:
>> >> OGAWA Hirofumi<hirofumi@xxxxxxxxxxxxxxxxxx> writes:
>> >>
>> >> > I noticed recently NMI on guest kernel is not working well.
>> >> host/guest
>> >> > kernel is 2.6.39-rc4, and using vmx.
>> >> >
>> >> > And test code is something like the following:
>> >> >
>> >> > local_irq_disable();
>> >> > for (i = 0; i< 10; i++) {
>> >> > int cpu = get_cpu();
>> >> > printk("%s: nmi %u, lapic %u\n", __FUNCTION__,
>> >> > nmi_count(cpu), irq_stat[cpu].apic_timer_irqs);
>> >> > mdelay(1000);
>> >> > put_cpu();
>> >> > }
>> >> >
>> >> > the result is both of nmi and lapic are not increased. If I used
>> >> > -no-kvm-irqchip, it works fine (increase nmi only). So, it
>> seems to be
>> >> > the bug of kvm driver side.
>> >>
>> >> With some debug, the cause seems to be in pit_do_work(). With the
>> >> following patch, NMI watchdog seems to be working correctly (if irq
>> >> disabled for long time, NMI watchdog can detect it).
>> >>
>> >> Is the following patch right?
>> >
>> > This would cause IRQs to be delivered even if the PIT is masked, no?
>> >
>> > Are you in fact using the PIT? Linux prefers the HPET, and in my
>> > experience the -no-hpet option makes NMIs work.
>>
>> BTW, that's another bug of the in-kernel PIT model: It disables the
>> timer in HPET legacy mode even if we are aware of NMI watchdog
>> receivers. Actually, the whole legacy disabling looks a bit strange in
>> the PIT (mode hackery + flag testing...).
>>
>> While this should be fixed/refactored, adding basic perf support to KVM
>> will be the only option long-term as Linux dropped virtual-wire NMI
>> watchdog support some releases ago.
>
> Yes. Unfortunately that is very vendor and model specific. The
> architectural PMU is supported, but that is only available on Intel.
Is it supposed to have any practical value already? I did not yet find a
magic -cpu switch to let Linux detect anything, not to speak of perf or
watchdog support.
>
> Perhaps we could emulate the architectural PMU on AMD as well, and make
> the detection code in the guest vendor agnostic. Since it's based on a
> cpuid bit, it should be safe.
>
We may only make Linux happy this way, no?
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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