linux-kernel - Re: [PATCH 34/61] KVM: x86: Handle RDTSCP CPUID adjustment in VMX code

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Message-ID: <87sgj0ngx0.fsf@vitty.brq.redhat.com>
Date:   Mon, 24 Feb 2020 16:28:27 +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 34/61] KVM: x86: Handle RDTSCP CPUID adjustment in VMX code

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

> Move the clearing of the RDTSCP CPUID bit into VMX, which has a separate
> VMCS control to enable RDTSCP in non-root, to eliminate an instance of
> the undesirable "unsigned f_* = *_supported ? F(*) : 0" pattern in the
> common CPUID handling code.  Drop ->rdtscp_supported() since CPUID
> adjustment was the last remaining user.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/cpuid.c   | 3 +--
>  arch/x86/kvm/vmx/vmx.c | 4 ++++
>  2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index a1f46b3ca16e..fc507270f3f3 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -424,7 +424,6 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  	unsigned f_gbpages = 0;
>  	unsigned f_lm = 0;
>  #endif
> -	unsigned f_rdtscp = kvm_x86_ops->rdtscp_supported() ? F(RDTSCP) : 0;
>  	unsigned f_xsaves = kvm_x86_ops->xsaves_supported() ? F(XSAVES) : 0;
>  	unsigned f_intel_pt = kvm_x86_ops->pt_supported() ? F(INTEL_PT) : 0;
>  
> @@ -446,7 +445,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		F(MTRR) | F(PGE) | F(MCA) | F(CMOV) |
>  		F(PAT) | F(PSE36) | 0 /* Reserved */ |
>  		f_nx | 0 /* Reserved */ | F(MMXEXT) | F(MMX) |
> -		F(FXSR) | F(FXSR_OPT) | f_gbpages | f_rdtscp |
> +		F(FXSR) | F(FXSR_OPT) | f_gbpages | F(RDTSCP) |
>  		0 /* Reserved */ | f_lm | F(3DNOWEXT) | F(3DNOW);
>  	/* cpuid 1.ecx */
>  	const u32 kvm_cpuid_1_ecx_x86_features =
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index a9728cc0c343..3990ba691d07 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7119,6 +7119,10 @@ static void vmx_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
>  		    boot_cpu_has(X86_FEATURE_OSPKE))
>  			cpuid_entry_set(entry, X86_FEATURE_PKU);
>  		break;
> +	case 0x80000001:
> +		if (!cpu_has_vmx_rdtscp())
> +			cpuid_entry_clear(entry, X86_FEATURE_RDTSCP);
> +		break;
>  	default:
>  		break;
>  	}

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

-- 
Vitaly