Re: [PATCH] KVM: x86: Avoid busy loops over uninjectable pending APIC timers

[Gleb Natapov <gleb@redhat.com>]

On Sun, Apr 28, 2013 at 12:20:12PM +0200, Jan Kiszka wrote:
> On 2013-04-28 12:19, Gleb Natapov wrote:
> > On Sun, Apr 28, 2013 at 12:15:05PM +0200, Jan Kiszka wrote:
> >> On 2013-03-17 09:47, Gleb Natapov wrote:
> >>> On Sat, Mar 16, 2013 at 09:49:07PM +0100, Jan Kiszka wrote:
> >>>> From: Jan Kiszka <jan.kiszka@siemens.com>
> >>>>
> >>>> If the guest didn't take the last APIC timer interrupt yet and generates
> >>>> another one on top, e.g. via periodic mode, we do not block the VCPU
> >>>> even if the guest state is halted. The reason is that
> >>>> apic_has_pending_timer continues to return a non-zero value.
> >>>>
> >>>> Fix this busy loop by taking the IRR content for the LVT vector in
> >>>> apic_has_pending_timer into account.
> >>>>
> >>> Just drop coalescing tacking for lapic interrupt. After posted interrupt
> >>> will be merged __apic_accept_irq() will not longer return coalescing
> >>> information, so the code will be dead anyway.
> >>
> >> If I understood the follow-up discussion correctly, we aren't dropping
> >> de-coalescing support yet. So how to proceed with this fix here?
> >>
> > We do. It does not work if you run on CPU with apicv support already.
> 
> But isn't the code still there and working when apicv is absent?
> 
Remove it as a fix for busy loop. It is not a good idea to behave differently on different
types of hardware.

--
			Gleb.