linux-kernel - Re: [PATCH v2 3/3] KVM: x86: use general helpers for some cpuid manipulation

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Message-ID: <ff689320-19b4-118c-ddea-287487d2f1de@redhat.com>
Date:   Mon, 7 Aug 2017 10:36:50 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 3/3] KVM: x86: use general helpers for some cpuid
 manipulation

On 05.08.2017 00:12, Radim Krčmář wrote:
> Add guest_cpuid_clear() and use it instead of kvm_find_cpuid_entry().
> Also replace some uses of kvm_find_cpuid_entry() with guest_cpuid_has().
> 
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
> v2: added __always_inline (Paolo)
> ---
>  arch/x86/kvm/cpuid.h |  9 +++++++++
>  arch/x86/kvm/svm.c   |  5 +----
>  arch/x86/kvm/vmx.c   |  6 ++----
>  arch/x86/kvm/x86.c   | 14 ++------------
>  4 files changed, 14 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index 4e9ac93b4f3a..ac15193e5e52 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -104,6 +104,15 @@ static __always_inline bool guest_cpuid_has(struct kvm_vcpu *vcpu, unsigned x86_
>  	return *reg & bit(x86_feature);
>  }
>  
> +static __always_inline void guest_cpuid_clear(struct kvm_vcpu *vcpu, unsigned x86_feature)
> +{
> +	int *reg;

you could instantiate it directly.

> +
> +	reg = guest_cpuid_get_register(vcpu, x86_feature);
> +	if (reg)
> +		*reg &= ~bit(x86_feature);
> +}
> +
>  static inline bool guest_cpuid_is_amd(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_cpuid_entry2 *best;
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index b8196aecbdcc..2432bb952a30 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5075,7 +5075,6 @@ static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
>  static void svm_cpuid_update(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_svm *svm = to_svm(vcpu);
> -	struct kvm_cpuid_entry2 *entry;
>  
>  	/* Update nrips enabled cache */
>  	svm->nrips_enabled = !!guest_cpuid_has(&svm->vcpu, X86_FEATURE_NRIPS);
> @@ -5083,9 +5082,7 @@ static void svm_cpuid_update(struct kvm_vcpu *vcpu)
>  	if (!kvm_vcpu_apicv_active(vcpu))
>  		return;
>  
> -	entry = kvm_find_cpuid_entry(vcpu, 1, 0);
> -	if (entry)
> -		entry->ecx &= ~bit(X86_FEATURE_X2APIC);
> +	guest_cpuid_clear(vcpu, X86_FEATURE_X2APIC);
>  }
>  
>  static void svm_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 85b73c1f963a..1731c7aca464 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -9472,15 +9472,13 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
>  
>  	if (vmx_invpcid_supported()) {
>  		/* Exposing INVPCID only when PCID is exposed */
> -		struct kvm_cpuid_entry2 *best = kvm_find_cpuid_entry(vcpu, 0x7, 0);
>  		bool invpcid_enabled =
> -			best && best->ebx & bit(X86_FEATURE_INVPCID) &&
> +			guest_cpuid_has(vcpu, X86_FEATURE_INVPCID) &&
>  			guest_cpuid_has(vcpu, X86_FEATURE_PCID);
>  
>  		if (!invpcid_enabled) {
>  			secondary_exec_ctl &= ~SECONDARY_EXEC_ENABLE_INVPCID;
> -			if (best)
> -				best->ebx &= ~bit(X86_FEATURE_INVPCID);
> +			guest_cpuid_clear(vcpu, X86_FEATURE_INVPCID);

just how I wanted it :)

>  		}
>  
>  		if (nested) {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ee4e251c82fc..33fd6b6419ef 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1022,21 +1022,11 @@ bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
>  	if (efer & efer_reserved_bits)
>  		return false;
>  
> -	if (efer & EFER_FFXSR) {
> -		struct kvm_cpuid_entry2 *feat;
> -
> -		feat = kvm_find_cpuid_entry(vcpu, 0x80000001, 0);
> -		if (!feat || !(feat->edx & bit(X86_FEATURE_FXSR_OPT)))
> +	if (efer & EFER_FFXSR && !guest_cpuid_has(vcpu, X86_FEATURE_FXSR_OPT))
>  			return false;
> -	}
>  
> -	if (efer & EFER_SVME) {
> -		struct kvm_cpuid_entry2 *feat;
> -
> -		feat = kvm_find_cpuid_entry(vcpu, 0x80000001, 0);
> -		if (!feat || !(feat->ecx & bit(X86_FEATURE_SVM)))
> +	if (efer & EFER_SVME && !guest_cpuid_has(vcpu, X86_FEATURE_SVM))
>  			return false;
> -	}
>  
>  	return true;
>  }
> 

Very nice cleanup.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 

Thanks,

David