linux-kernel - Re: [PART1 RFC v2 06/10] svm: Add interrupt injection via AVIC

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Date:	Mon, 14 Mar 2016 13:27:00 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Radim Krčmář <rkrcmar@...hat.com>
Cc:	joro@...tes.org, bp@...en8.de, gleb@...nel.org,
	alex.williamson@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, wei@...hat.com,
	sherry.hurwitz@....com
Subject: Re: [PART1 RFC v2 06/10] svm: Add interrupt injection via AVIC



On 14/03/2016 10:41, Suravee Suthikulpanit wrote:
>>>>>>
>>>>>> +    kvm_lapic_set_vector(vec, avic_get_bk_page_entry(svm,
>>>>>> APIC_IRR));
>>>>
>>>> (I think that smp_mb here would make sense, even though we're fine now
>>>>   thanks to re-checking vcpu->mode in kvm_vcpu_kick.
>>>
>>> Right, though only a smp_mb__after_atomic() is required (which is a
>>> compiler barrier).  It is similarly required in vmx.
>>
>> True, kvm_lapic_set_vector uses a lock prefix.
>>
>> (I thought it behaves like atomic_set, which would require MFENCE for
>>   correct ordering here ... I don't like smp_mb__after_atomic much
>>   because of the discrepancy on some atomic operations.)
>>
> 
> So, should i just use smb_mb() in this case?

You should use smp_mb__after_atomic().

Paolo