[RFC PATCH 26/27] KVM: x86: Add a helper to query the allowed CPUID mask

[Binbin Wu <binbin.wu@linux.intel.com>]

Add and export kvm_cpuid_get_allowed_mask() to let vendor modules (e.g.,
TDX) look up the allowed bitmask for a specific CPUID leaf/subleaf/
register under a given overlay.

TDX is probably the only user, CPUID features emulated are not
included.

Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
---
 arch/x86/kvm/cpuid.c | 16 ++++++++++++++++
 arch/x86/kvm/cpuid.h |  1 +
 2 files changed, 17 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index e6f0ecadc290..30fb61c1430d 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -526,6 +526,22 @@ static int kvm_check_pv_cpuid_relocated(struct kvm_vcpu *vcpu, struct kvm_cpuid_
 	return 0;
 }
 
+/* CPUID features emulated are not included. */
+u32 kvm_cpuid_get_allowed_mask(u32 func, u32 index, int reg, u32 overlay)
+{
+	u32 leaf;
+
+	if (is_cpuid_paranoid_ignored(func, index, reg, overlay))
+		return (u32)-1;
+
+	leaf = cpuid_reg_2_x86_leaf(func, index, reg);
+	if (leaf == (u32)-1)
+		return 0;
+
+	return kvm_cpu_caps[overlay][leaf];
+}
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_cpuid_get_allowed_mask);
+
 static int cpuid_check_and_set_vcpu_caps(struct kvm_vcpu *vcpu,
 					 struct kvm_cpuid_entry2 *entry)
 {
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index cff5e71579ce..251003d78990 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -85,6 +85,7 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
 			      struct kvm_cpuid_entry2 __user *entries);
 bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 	       u32 *ecx, u32 *edx, bool exact_only);
+u32 kvm_cpuid_get_allowed_mask(u32 func, u32 index, int reg, u32 overlay);
 
 void __init kvm_init_xstate_sizes(void);
 u32 xstate_required_size(u64 xstate_bv, bool compacted);
-- 
2.46.0