Re: [PATCH] KVM: x86: use inlines instead of macros for is_sev_*guest

[Sean Christopherson <seanjc@google.com>]

On Mon, Apr 13, 2026, Paolo Bonzini wrote:
> This helps avoiding more embarrassment to this maintainer,

Not building SEV support before pushing to kvm/queue is certainly a choice :-D

> but also will catch mistakes more easily for others.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/svm/svm.h | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index fd0652b32c81..a10668d17a16 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -422,9 +422,19 @@ static __always_inline bool is_sev_snp_guest(struct kvm_vcpu *vcpu)
>  	return ____sev_snp_guest(vcpu->kvm);
>  }
>  #else
> -#define is_sev_guest(vcpu) false
> -#define is_sev_es_guest(vcpu) false
> -#define is_sev_snp_guest(vcpu) false
> +static __always_inline bool is_sev_guest(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +static __always_inline bool is_sev_es_guest(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +
> +static __always_inline bool is_sev_snp_guest(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}

As called out in commit 45d522d3ee9c ("KVM: SVM: Macrofy SEV=n versions of
sev_xxx_guest()"), use of macros is intentional as gcc-12 at least generates
suboptimal code if there's a proper function.

That said, gcc-11 (I don't think I have gcc-12 laying around anywhere) generates
identical code for all of kvm-amd.ko with and without macros, so maybe whatever I
saw a transient issue?  I don't have a strong motivation for caring about any
version of gcc, so I'm a-ok using __always_inline functions.

Alternatively, e.g. if a "bad code generation" issue pops up again, we could use
BUILD_BUG_ON_INVALID() to validate the input.

diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 5440486a3d32..3f572f30f28c 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -425,19 +425,9 @@ static __always_inline bool is_sev_snp_guest(struct kvm_vcpu *vcpu)
        return ____sev_snp_guest(vcpu->kvm);
 }
 #else
-static __always_inline bool is_sev_guest(struct kvm_vcpu *vcpu)
-{
-       return false;
-}
-static __always_inline bool is_sev_es_guest(struct kvm_vcpu *vcpu)
-{
-       return false;
-}
-
-static __always_inline bool is_sev_snp_guest(struct kvm_vcpu *vcpu)
-{
-       return false;
-}
+#define is_sev_guest(vcpu) ({ BUILD_BUG_ON_INVALID((vcpu)->kvm); false; })
+#define is_sev_es_guest(vcpu) ({ BUILD_BUG_ON_INVALID((vcpu)->kvm); false; })
+#define is_sev_snp_guest(vcpu) ({ BUILD_BUG_ON_INVALID((vcpu)->kvm); false; })
 #endif
 
 static inline bool ghcb_gpa_is_registered(struct vcpu_svm *svm, u64 val)