linux-kernel - Re: [PATCH] KVM: x86: VMX: hyper-v: Enlightened MSR-Bitmap support

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Message-ID: <ef082ed6-1af9-a578-d9da-e0874cc4769c@redhat.com>
Date:   Fri, 13 Apr 2018 15:52:30 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     x86@...nel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        Mohammed Gamal <mmorsy@...hat.com>,
        Cathy Avery <cavery@...hat.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: VMX: hyper-v: Enlightened MSR-Bitmap support

On 12/04/2018 17:25, Vitaly Kuznetsov wrote:
> @@ -5335,6 +5353,9 @@ static void __always_inline vmx_disable_intercept_for_msr(unsigned long *msr_bit
>  	if (!cpu_has_vmx_msr_bitmap())
>  		return;
>  
> +	if (static_branch_unlikely(&enable_emsr_bitmap))
> +		evmcs_touch_msr_bitmap();
> +
>  	/*
>  	 * See Intel PRM Vol. 3, 20.6.9 (MSR-Bitmap Address). Early manuals
>  	 * have the write-low and read-high bitmap offsets the wrong way round.
> @@ -5370,6 +5391,9 @@ static void __always_inline vmx_enable_intercept_for_msr(unsigned long *msr_bitm
>  	if (!cpu_has_vmx_msr_bitmap())
>  		return;
>  
> +	if (static_branch_unlikely(&enable_emsr_bitmap))
> +		evmcs_touch_msr_bitmap();

I'm not sure about the "unlikely".  Can you just check current_evmcs
instead (dropping the static key completely)?

The function, also, is small enough that inlining should be beneficial.

Paolo