linux-kernel - Re: [PATCH 42/61] KVM: x86: Add a helper to check kernel support when setting cpu cap

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Message-ID: <875zfvodwx.fsf@vitty.brq.redhat.com>
Date:   Mon, 24 Feb 2020 22:47:58 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 42/61] KVM: x86: Add a helper to check kernel support when setting cpu cap

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Add a helper, kvm_cpu_cap_check_and_set(), to query boot_cpu_has() as
> part of setting a KVM cpu capability.  VMX in particular has a number of
> features that are dependent on both a VMCS capability and kernel
> support.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/cpuid.h   |  6 ++++++
>  arch/x86/kvm/svm.c     |  3 +--
>  arch/x86/kvm/vmx/vmx.c | 18 ++++++++----------
>  3 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index c64283582d96..7b71ae0ca05e 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -274,4 +274,10 @@ static __always_inline void kvm_cpu_cap_set(unsigned x86_feature)
>  	kvm_cpu_caps[x86_leaf] |= __feature_bit(x86_feature);
>  }
>  
> +static __always_inline void kvm_cpu_cap_check_and_set(unsigned x86_feature)
> +{
> +	if (boot_cpu_has(x86_feature))
> +		kvm_cpu_cap_set(x86_feature);
> +}
> +
>  #endif
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 7cb05945162e..defb2c0dbf8a 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1362,8 +1362,7 @@ static __init void svm_set_cpu_caps(void)
>  
>  	/* CPUID 0x8000000A */
>  	/* Support next_rip if host supports it */
> -	if (boot_cpu_has(X86_FEATURE_NRIPS))
> -		kvm_cpu_cap_set(X86_FEATURE_NRIPS);
> +	kvm_cpu_cap_check_and_set(X86_FEATURE_NRIPS);
>  
>  	if (npt_enabled)
>  		kvm_cpu_cap_set(X86_FEATURE_NPT);
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index cfd0ef314176..cecf59225136 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7118,18 +7118,16 @@ static __init void vmx_set_cpu_caps(void)
>  		kvm_cpu_cap_set(X86_FEATURE_VMX);
>  
>  	/* CPUID 0x7 */
> -	if (boot_cpu_has(X86_FEATURE_MPX) && kvm_mpx_supported())
> -		kvm_cpu_cap_set(X86_FEATURE_MPX);
> -	if (boot_cpu_has(X86_FEATURE_INVPCID) && cpu_has_vmx_invpcid())
> -		kvm_cpu_cap_set(X86_FEATURE_INVPCID);
> -	if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&
> -	    vmx_pt_mode_is_host_guest())
> -		kvm_cpu_cap_set(X86_FEATURE_INTEL_PT);
> +	if (kvm_mpx_supported())
> +		kvm_cpu_cap_check_and_set(X86_FEATURE_MPX);
> +	if (cpu_has_vmx_invpcid())
> +		kvm_cpu_cap_check_and_set(X86_FEATURE_INVPCID);
> +	if (vmx_pt_mode_is_host_guest())
> +		kvm_cpu_cap_check_and_set(X86_FEATURE_INTEL_PT);
>  
>  	/* PKU is not yet implemented for shadow paging. */
> -	if (enable_ept && boot_cpu_has(X86_FEATURE_PKU) &&
> -	    boot_cpu_has(X86_FEATURE_OSPKE))
> -		kvm_cpu_cap_set(X86_FEATURE_PKU);
> +	if (enable_ept && boot_cpu_has(X86_FEATURE_OSPKE))
> +		kvm_cpu_cap_check_and_set(X86_FEATURE_PKU);
>  
>  	/* CPUID 0xD.1 */
>  	if (!vmx_xsaves_supported())

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly