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

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Date:	Fri, 04 Mar 2016 15:12:14 +0800
From:	Lan Tianyu <tianyu.lan@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	gleb@...nel.org, pbonzini@...hat.com, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, 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 2016年03月04日 15:21, Thomas Gleixner wrote:
> On Fri, 4 Mar 2016, 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
> 
> You want to leave the comment explaining the memory barriers and tell that
> kvm_flush_remote_tlbs() contains the smp_mb().

That sounds more reasonable. Will update. Thanks.

> 
>> -	 */
>> -	smp_mb();
>> -
>> -	/*
>>  	 * Wait for all vcpus to exit guest mode and/or lockless shadow
>>  	 * page table walks.
>>  	 */
>> -- 
>> 1.8.4.rc0.1.g8f6a3e5.dirty
>>
>>


-- 
Best regards
Tianyu Lan