Subject: Re: [PATCH] KVM: Remove redundant smp_mb() in the
 kvm_mmu_commit_zap_page()
To: Xiao Guangrong <guangrong.xiao@linux.intel.com>,
        Lan Tianyu <tianyu.lan@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>
References: <1457055312-27067-1-git-send-email-tianyu.lan@intel.com>
 <alpine.DEB.2.11.1603040820100.3597@nanos> <56D9354E.9040908@intel.com>
 <56D94BFE.1080406@redhat.com> <56DE8F1A.9000401@intel.com>
 <56DEEF69.20208@redhat.com> <56E1875E.8060007@linux.intel.com>
Cc: gleb@kernel.org, mingo@redhat.com, hpa@zytor.com, x86@kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <56E19224.9090906@redhat.com>
Date: Thu, 10 Mar 2016 16:26:28 +0100
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On 10/03/2016 15:40, Xiao Guangrong wrote:
>      long dirty_count = kvm->tlbs_dirty;
> 
> +        /*
> +         * read tlbs_dirty before doing tlb flush to make sure not tlb
> request is
> +         * lost.
> +         */
>      smp_mb();
> +
>      if (kvm_make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
>          ++kvm->stat.remote_tlb_flush;
>      cmpxchg(&kvm->tlbs_dirty, dirty_count, 0);
> 
> 
> Any comment?

Compared to smp_load_acquire(), smp_mb() adds an ordering between stores
and loads.  Is the

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