linux-kernel - Re: [PATCH] KVM: Remove redundant smp_mb() in the kvm_mmu_commit_zap

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Date:	Fri, 4 Mar 2016 21:48:22 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Lan Tianyu <tianyu.lan@...el.com>, gleb@...nel.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, x86@...nel.org
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: Remove redundant smp_mb() in the
 kvm_mmu_commit_zap_page()



On 03/04/2016 04:04 PM, Paolo Bonzini wrote:
> On 04/03/2016 02:35, Lan Tianyu wrote:
>> The following kvm_flush_remote_tlbs() will call smp_mb() inside and so
>> remove smp_mb() here.
>>
>> Signed-off-by: Lan Tianyu <tianyu.lan@...el.com>
>> ---
>>   arch/x86/kvm/mmu.c | 6 ------
>>   1 file changed, 6 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index a54ecd9..6315416 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -2383,12 +2383,6 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
>>   		return;
>>
>>   	/*
>> -	 * wmb: make sure everyone sees our modifications to the page tables
>> -	 * rmb: make sure we see changes to vcpu->mode
>> -	 */
>> -	smp_mb();
>> -
>> -	/*
>>   	 * Wait for all vcpus to exit guest mode and/or lockless shadow
>>   	 * page table walks.
>>   	 */
>>
>
> kvm_flush_remote_tlbs loads kvm->tlbs_dirty before issuing the memory
> barrier.  I think it's okay if the load is done earlier, but I'd like
> Guangrong to take a look.

Yes, It looks good to me, but please keep the comment.

Thanks!