Message-ID: <5A53C1DA.50901@ORACLE.COM>
Date: Mon, 08 Jan 2018 21:09:14 +0200
From: Liran Alon <LIRAN.ALON@ORACLE.COM>
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To: Paolo Bonzini <pbonzini@redhat.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
CC: jmattson@google.com, aliguori@amazon.com, thomas.lendacky@amd.com,
        dwmw@amazon.co.uk, bp@alien8.de
Subject: Re: [PATCH 1/7] KVM: x86: add SPEC_CTRL and IBPB_SUPPORT accessors
References: <1515434925-10250-1-git-send-email-pbonzini@redhat.com> <1515434925-10250-2-git-send-email-pbonzini@redhat.com>
In-Reply-To: <1515434925-10250-2-git-send-email-pbonzini@redhat.com>
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On 08/01/18 20:08, Paolo Bonzini wrote:
> As an interim measure until SPEC_CTRL is supported by upstream
> Linux in cpufeatures, add a function that lets vmx.c and svm.c
> know whether to save/restore MSR_IA32_SPEC_CTRL.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   arch/x86/kvm/cpuid.c |  3 ---
>   arch/x86/kvm/cpuid.h | 22 ++++++++++++++++++++++
>   2 files changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 8e9a07c557f1..767af697c20c 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -67,9 +67,6 @@ u64 kvm_supported_xcr0(void)
>
>   #define F(x) bit(X86_FEATURE_##x)
>
> -/* These are scattered features in cpufeatures.h. */
> -#define KVM_CPUID_BIT_AVX512_4VNNIW     2
> -#define KVM_CPUID_BIT_AVX512_4FMAPS     3
>   #define KF(x) bit(KVM_CPUID_BIT_##x)
>
>   int kvm_update_cpuid(struct kvm_vcpu *vcpu)
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index c2cea6651279..8d04ccf177ce 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -155,6 +155,28 @@ static inline int guest_cpuid_stepping(struct kvm_vcpu *vcpu)
>   	return x86_stepping(best->eax);
>   }
>
> +/* These are scattered features in cpufeatures.h. */
> +#define KVM_CPUID_BIT_AVX512_4VNNIW	2
> +#define KVM_CPUID_BIT_AVX512_4FMAPS	3
> +#define KVM_CPUID_BIT_SPEC_CTRL		26
> +#define KVM_CPUID_BIT_STIBP		27
> +
> +/* CPUID[eax=0x80000008].ebx */
> +#define KVM_CPUID_BIT_IBPB_SUPPORT	12
> +
> +static inline bool cpu_has_spec_ctrl(void)
> +{
> +	u32 eax, ebx, ecx, edx;
> +	cpuid_count(7, 0, &eax, &ebx, &ecx, &edx);
> +
> +	return edx & bit(KVM_CPUID_BIT_SPEC_CTRL);

Why not just "return cpuid_edx(7) & bit(KVM_CPUID_BIT_SPEC_CTRL);"?
This is also consistent with how cpu_has_ibpb_support() is written.

> +}
> +
> +static inline bool cpu_has_ibpb_support(void)
> +{
> +	return cpuid_ebx(0x80000008) & bit(KVM_CPUID_BIT_IBPB_SUPPORT);
> +}
> +
>   static inline bool supports_cpuid_fault(struct kvm_vcpu *vcpu)
>   {
>   	return vcpu->arch.msr_platform_info & MSR_PLATFORM_INFO_CPUID_FAULT;
>