Re: [PATCH stable] KVM: x86: Fix lost interrupt on irr_pending race

[Luis Henriques <luis.henriques@canonical.com>]

On Wed, Apr 22, 2015 at 03:47:04PM +0200, Paolo Bonzini wrote:
> 
> 
> On 22/04/2015 15:34, Luis Henriques wrote:
> > Thanks Paolo.  I was going to apply this backport to the 3.16 kernel
> > but it looks like the original commit is a clean cherry-pick.  Shall I
> > still apply your backport, or do you think the original commit should
> > be applied instead?
> 
> Indeed you're right.  I wrote the backport for 3.16(.0).  However,
> commit 56cc2406d68c0f09505c389e276f27a99f495cbd was marked for stable,
> so it's necessary to cherry-pick the entire patch on the stable kernel
> where the buggy commit was backported.
> 
> That should be, according to the stable@vger.kernel.org archives,
> 3.10.54+, 3.13.11.7+, 3.14.18+, 3.16.2+.
> 

Great, thanks for the quick reply.  I'll queue the (entire) fix for
the 3.16 kernel.

Cheers,
--
Luís

> Paolo
> 
> > Cheers,
> > --
> > Luís
> > 
> >> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> >> index 6e8ce5a1a05d..e0e5642dae41 100644
> >> --- a/arch/x86/kvm/lapic.c
> >> +++ b/arch/x86/kvm/lapic.c
> >> @@ -341,8 +341,12 @@ EXPORT_SYMBOL_GPL(kvm_apic_update_irr);
> >>  
> >>  static inline void apic_set_irr(int vec, struct kvm_lapic *apic)
> >>  {
> >> -	apic->irr_pending = true;
> >>  	apic_set_vector(vec, apic->regs + APIC_IRR);
> >> +	/*
> >> +	 * irr_pending must be true if any interrupt is pending; set it after
> >> +	 * APIC_IRR to avoid race with apic_clear_irr
> >> +	 */
> >> +	apic->irr_pending = true;
> >>  }
> >>  
> >>  static inline int apic_search_irr(struct kvm_lapic *apic)
> >>
> >>
> >> Thanks,
> >>
> >> Paolo
> >> --
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