linux-kernel - Re: [PATCH] KVM: x86: Use cpu_feature_enabled() for PKU instead of #ifdef

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Message-ID: <C8324338-FC07-454E-9A5A-1785141FEAB3@nutanix.com>
Date:   Fri, 2 Jun 2023 15:51:31 +0000
From:   Jon Kohler <jon@...anix.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: Use cpu_feature_enabled() for PKU instead of
 #ifdef



> On Jun 1, 2023, at 9:05 PM, Sean Christopherson <seanjc@...gle.com> wrote:
> 
> Replace an #ifdef on CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS with a
> cpu_feature_enabled() check on X86_FEATURE_PKU.  The macro magic of
> DISABLED_MASK_BIT_SET() means that cpu_feature_enabled() provides the
> same end result (no code generated) when PKU is disabled by Kconfig.
> 
> No functional change intended.
> 
> Cc: Jon Kohler <jon@...anix.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
> arch/x86/kvm/x86.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ceb7c5e9cf9e..eed1f0629023 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1017,13 +1017,11 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
> 			wrmsrl(MSR_IA32_XSS, vcpu->arch.ia32_xss);
> 	}
> 
> -#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> -	if (static_cpu_has(X86_FEATURE_PKU) &&
> +	if (cpu_feature_enabled(X86_FEATURE_PKU) &&
> 	    vcpu->arch.pkru != vcpu->arch.host_pkru &&
> 	    ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
> 	     kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE)))
> 		write_pkru(vcpu->arch.pkru);
> -#endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */
> }
> EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
> 
> @@ -1032,15 +1030,13 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
> 	if (vcpu->arch.guest_state_protected)
> 		return;
> 
> -#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> -	if (static_cpu_has(X86_FEATURE_PKU) &&
> +	if (cpu_feature_enabled(X86_FEATURE_PKU) &&
> 	    ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
> 	     kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) {
> 		vcpu->arch.pkru = rdpkru();
> 		if (vcpu->arch.pkru != vcpu->arch.host_pkru)
> 			write_pkru(vcpu->arch.host_pkru);
> 	}
> -#endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */
> 
> 	if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
> 
> 
> base-commit: a053a0e4a9f8c52f3acf8a9d2520c4bf39077a7e
> -- 
> 2.41.0.rc2.161.g9c6817b8e7-goog
> 

Thanks for the cleanup!

Reviewed-by: Jon Kohler <jon@...anix.com>