Re: [PATCH v3 01/10] KVM: x86/mmu: Change tdp_mmu to a read-only parameter

[Sean Christopherson <seanjc@google.com>]

On Wed, Sep 21, 2022, David Matlack wrote:
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 6bdaacb6faa0..168c46fd8dd1 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -230,14 +230,14 @@ static inline bool kvm_shadow_root_allocated(struct kvm *kvm)
>  }
>  
>  #ifdef CONFIG_X86_64
> -static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return kvm->arch.tdp_mmu_enabled; }
> +extern bool tdp_mmu_enabled;
>  #else
> -static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }
> +#define tdp_mmu_enabled false
>  #endif

Rather than open code references to the variable, keep the wrappers so that the
guts can be changed without needing to churn a pile of code.  I'll follow-up in
the "Split out TDP MMU page fault handling" with the reasoning.

E.g.

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 6bdaacb6faa0..1ad6d02e103f 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -230,14 +230,21 @@ static inline bool kvm_shadow_root_allocated(struct kvm *kvm)
 }
 
 #ifdef CONFIG_X86_64
-static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return kvm->arch.tdp_mmu_enabled; }
+extern bool tdp_mmu_enabled;
+#endif
+
+static inline bool is_tdp_mmu_enabled(void)
+{
+#ifdef CONFIG_X86_64
+	return tdp_mmu_enabled;
 #else
-static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }
+	return false;
 #endif
+}
 
 static inline bool kvm_memslots_have_rmaps(struct kvm *kvm)
 {
-	return !is_tdp_mmu_enabled(kvm) || kvm_shadow_root_allocated(kvm);
+	return !is_tdp_mmu_enabled() || kvm_shadow_root_allocated(kvm);
 }
 
 static inline gfn_t gfn_to_index(gfn_t gfn, gfn_t base_gfn, int level)