linux-kernel - Re: [PATCH V3 2/13] KVM/MMU: Add tlb flush with range helper function

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Date:   Mon, 1 Oct 2018 17:25:54 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tianyu Lan <Tianyu.Lan@...rosoft.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        vkuznets <vkuznets@...hat.com>,
        Jork Loeser <Jork.Loeser@...rosoft.com>
Subject: Re: [PATCH V3 2/13] KVM/MMU: Add tlb flush with range helper function

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);
> +}
> +