linux-kernel - Re: [PATCH stable] KVM: x86: Fix lost interrupt on irr

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Date:	Wed, 22 Apr 2015 15:47:04 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Luis Henriques <luis.henriques@...onical.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	saso.linux@...im.si, lists2009@...rfbargle.com,
	Nadav Amit <namit@...technion.ac.il>, stable@...r.kernel.org
Subject: Re: [PATCH stable] KVM: x86: Fix lost interrupt on irr_pending race



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@...r.kernel.org archives,
3.10.54+, 3.13.11.7+, 3.14.18+, 3.16.2+.

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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