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

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Message-ID: <56E1933E.20909@redhat.com>
Date:	Thu, 10 Mar 2016 16:31:10 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Lan Tianyu <tianyu.lan@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	gleb@...nel.org, 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 10/03/2016 16:26, Paolo Bonzini wrote:
> Compared to smp_load_acquire(), smp_mb() adds an ordering between stores
> and loads.

Here, the ordering is load-store, hence...

> The load of kvm->tlbs_dirty should then be
> 
> 	/*
> 	 * Read tlbs_dirty before setting KVM_REQ_TLB_FLUSH in
> 	 * kvm_make_all_cpus_request.  This
> 	 */
> 	long dirty_count = smp_load_acquire(kvm->tlbs_dirty);
> 
> Tianyu, I think Xiao provided the information that I was missing.  Would
> you like to prepare the patch?

Thanks,

Paolo