Re: [PATCH 25/33] KVM: x86: expose cpuid_entry2_find for TDX

["Huang, Kai" <kai.huang@intel.com>]

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On 27/02/2025 7:14 am, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Kai Huang <kai.huang@intel.com>

... assuming there will be a changelog, e.g., perhaps something like below:

TDX will need to search a CPUID leaf from a list of per-TD scope CPUID 
entries w/o any vCPU context.  Abstract the code which does CPUID entry 
search from a given list of CPUID entries as kvm_find_cpuid_entry2() and 
Export it for TDX to use.

And one nit below ...

> @@ -141,23 +141,26 @@ static struct kvm_cpuid_entry2 *cpuid_entry2_find(struct kvm_vcpu *vcpu,
>   
>   	return NULL;
>   }
> +EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry2);
>   
>   struct kvm_cpuid_entry2 *kvm_find_cpuid_entry_index(struct kvm_vcpu *vcpu,
>   						    u32 function, u32 index)
>   {
> -	return cpuid_entry2_find(vcpu, function, index);
> +	return kvm_find_cpuid_entry2(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent,
> +				     function, index);
>   }
>   EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry_index);
>   
>   struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
>   					      u32 function)
>   {
> -	return cpuid_entry2_find(vcpu, function, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
> +	return kvm_find_cpuid_entry2(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent,
> +				     function, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
>   }
>   EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry);

... I think we can change both kvm_find_cpuid_entry_index() and 
kvm_find_cpuid_entry() to 'static inline' and place them in the 
kvm/cpuid.h to avoid exporting them.

See attached diff.  Build test only.

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diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 7ff84079c1f4..ecf2750693d4 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -143,22 +143,6 @@ struct kvm_cpuid_entry2 *kvm_find_cpuid_entry2(
 }
 EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry2);
 
-struct kvm_cpuid_entry2 *kvm_find_cpuid_entry_index(struct kvm_vcpu *vcpu,
-						    u32 function, u32 index)
-{
-	return kvm_find_cpuid_entry2(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent,
-				     function, index);
-}
-EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry_index);
-
-struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
-					      u32 function)
-{
-	return kvm_find_cpuid_entry2(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent,
-				     function, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
-}
-EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry);
-
 /*
  * kvm_find_cpuid_entry2() and KVM_CPUID_INDEX_NOT_SIGNIFICANT should never be used
  * directly outside of kvm_find_cpuid_entry() and kvm_find_cpuid_entry_index().
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 46e059b47825..738b396416cd 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -14,10 +14,29 @@ void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu);
 void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu);
 struct kvm_cpuid_entry2 *kvm_find_cpuid_entry2(struct kvm_cpuid_entry2 *entries,
 					       int nent, u32 function, u64 index);
-struct kvm_cpuid_entry2 *kvm_find_cpuid_entry_index(struct kvm_vcpu *vcpu,
-						    u32 function, u32 index);
-struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
-					      u32 function);
+/*
+ * Magic value used by KVM when querying userspace-provided CPUID entries and
+ * doesn't care about the CPIUD index because the index of the function in
+ * question is not significant.  Note, this magic value must have at least one
+ * bit set in bits[63:32] and must be consumed as a u64 by kvm_find_cpuid_entry2()
+ * to avoid false positives when processing guest CPUID input.
+ */
+#define KVM_CPUID_INDEX_NOT_SIGNIFICANT -1ull
+
+static inline struct kvm_cpuid_entry2 *kvm_find_cpuid_entry_index(struct kvm_vcpu *vcpu,
+								  u32 function, u32 index)
+{
+	return kvm_find_cpuid_entry2(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent,
+				     function, index);
+}
+
+static inline struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
+							    u32 function)
+{
+	return kvm_find_cpuid_entry2(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent,
+				     function, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
+}
+
 int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
 			    struct kvm_cpuid_entry2 __user *entries,
 			    unsigned int type);