linux-kernel - Re: [PATCH v3 03/15] KVM: SVM: Invert handling of SEV and SEV

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Date: Tue, 12 Mar 2024 10:19:02 -0500
From: Michael Roth <michael.roth@....com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<seanjc@...gle.com>, <aik@....com>
Subject: Re: [PATCH v3 03/15] KVM: SVM: Invert handling of SEV and SEV_ES
 feature flags

On Mon, Feb 26, 2024 at 02:03:32PM -0500, Paolo Bonzini wrote:
> From: Sean Christopherson <seanjc@...gle.com>
> 
> Leave SEV and SEV_ES '0' in kvm_cpu_caps by default, and instead set them
> in sev_set_cpu_caps() if SEV and SEV-ES support are fully enabled.  Aside
> from the fact that sev_set_cpu_caps() is wildly misleading when it *clears*
> capabilities, this will allow compiling out sev.c without falsely
> advertising SEV/SEV-ES support in KVM_GET_SUPPORTED_CPUID.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: Michael Roth <michael.roth@....com>

> ---
>  arch/x86/kvm/cpuid.c   | 2 +-
>  arch/x86/kvm/svm/sev.c | 8 ++++----
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index adba49afb5fe..bde4df13a7e8 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -761,7 +761,7 @@ void kvm_set_cpu_caps(void)
>  	kvm_cpu_cap_mask(CPUID_8000_000A_EDX, 0);
>  
>  	kvm_cpu_cap_mask(CPUID_8000_001F_EAX,
> -		0 /* SME */ | F(SEV) | 0 /* VM_PAGE_FLUSH */ | F(SEV_ES) |
> +		0 /* SME */ | 0 /* SEV */ | 0 /* VM_PAGE_FLUSH */ | 0 /* SEV_ES */ |
>  		F(SME_COHERENT));
>  
>  	kvm_cpu_cap_mask(CPUID_8000_0021_EAX,
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index f06f9e51ad9d..aec3453fd73c 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2178,10 +2178,10 @@ void sev_vm_destroy(struct kvm *kvm)
>  
>  void __init sev_set_cpu_caps(void)
>  {
> -	if (!sev_enabled)
> -		kvm_cpu_cap_clear(X86_FEATURE_SEV);
> -	if (!sev_es_enabled)
> -		kvm_cpu_cap_clear(X86_FEATURE_SEV_ES);
> +	if (sev_enabled)
> +		kvm_cpu_cap_set(X86_FEATURE_SEV);
> +	if (sev_es_enabled)
> +		kvm_cpu_cap_set(X86_FEATURE_SEV_ES);
>  }
>  
>  void __init sev_hardware_setup(void)
> -- 
> 2.39.1
> 
>