linux-kernel - Re: [PATCH] x86/kvm/svm: Simplify cpu_has

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Date:	Thu, 9 Jun 2016 17:19:56 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Borislav Petkov <bp@...en8.de>, LKML <linux-kernel@...r.kernel.org>
Cc:	Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/kvm/svm: Simplify cpu_has_svm()



On 09/05/2016 11:53, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> Use already cached CPUID information instead of querying CPUID again.
> 
> No functionality change.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: kvm@...r.kernel.org
> Cc: x86@...nel.org
> ---
>  arch/x86/include/asm/svm.h     | 1 -
>  arch/x86/include/asm/virtext.h | 8 ++------
>  2 files changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index 6136d99f537b..41888f51f936 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -185,7 +185,6 @@ struct __attribute__ ((__packed__)) vmcb {
>  	struct vmcb_save_area save;
>  };
>  
> -#define SVM_CPUID_FEATURE_SHIFT 2
>  #define SVM_CPUID_FUNC 0x8000000a
>  
>  #define SVM_VM_CR_SVM_DISABLE 4
> diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h
> index cce9ee68e335..0116b2ee9e64 100644
> --- a/arch/x86/include/asm/virtext.h
> +++ b/arch/x86/include/asm/virtext.h
> @@ -83,23 +83,19 @@ static inline void cpu_emergency_vmxoff(void)
>   */
>  static inline int cpu_has_svm(const char **msg)
>  {
> -	uint32_t eax, ebx, ecx, edx;
> -
>  	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
>  		if (msg)
>  			*msg = "not amd";
>  		return 0;
>  	}
>  
> -	cpuid(0x80000000, &eax, &ebx, &ecx, &edx);
> -	if (eax < SVM_CPUID_FUNC) {
> +	if (boot_cpu_data.extended_cpuid_level < SVM_CPUID_FUNC) {
>  		if (msg)
>  			*msg = "can't execute cpuid_8000000a";
>  		return 0;
>  	}
>  
> -	cpuid(0x80000001, &eax, &ebx, &ecx, &edx);
> -	if (!(ecx & (1 << SVM_CPUID_FEATURE_SHIFT))) {
> +	if (!boot_cpu_has(X86_FEATURE_SVM)) {
>  		if (msg)
>  			*msg = "svm not available";
>  		return 0;
> 

Queued, thanks.

Paolo