Re: nmi is broken?

[Avi Kivity <avi@redhat.com>]

On 04/24/2011 01:50 AM, OGAWA Hirofumi wrote:
> OGAWA Hirofumi<hirofumi@mail.parknet.co.jp>  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.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.