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Subject: Re: [PATCH V3 2/13] KVM/MMU: Add tlb flush with range helper function
To:     Tianyu Lan <Tianyu.Lan@microsoft.com>
Cc:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "hpa@zytor.com" <hpa@zytor.com>, "x86@kernel.org" <x86@kernel.org>,
        "rkrcmar@redhat.com" <rkrcmar@redhat.com>,
        "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>,
        vkuznets <vkuznets@redhat.com>,
        Jork Loeser <Jork.Loeser@microsoft.com>
References: <20180927034829.2230-1-Tianyu.Lan@microsoft.com>
 <20180927034829.2230-3-Tianyu.Lan@microsoft.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Message-ID: <2ab49b6e-59d1-1b1f-b533-85e5bc49dd85@redhat.com>
Date:   Mon, 1 Oct 2018 17:25:54 +0200
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In-Reply-To: <20180927034829.2230-3-Tianyu.Lan@microsoft.com>
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On 27/09/2018 05:48, Tianyu Lan wrote:
> +
> +	if (range && kvm_x86_ops->tlb_remote_flush_with_range) {
> +		/*
> +		 * Read tlbs_dirty before flushing tlbs in order
> +		 * to track dirty tlbs during flushing.
> +		 */
> +		long dirty_count = smp_load_acquire(&kvm->tlbs_dirty);
> +
> +		ret = kvm_x86_ops->tlb_remote_flush_with_range(kvm, range);
> +		cmpxchg(&kvm->tlbs_dirty, dirty_count, 0);

This is wrong, because it's not the entire TLB that is flushed.  So you
cannot do the cmpxchg here.

Paolo

> +
> +	if (ret)
> +		kvm_flush_remote_tlbs(kvm);
> +}
> +