[RFC PATCH 09/27] KVM: x86: Use overlays of KVM CPU capabilities

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

Select the appropriate CPUID overlay based on the VM type or/and hardware
vendor rather than using CPUID_OL_DEFAULT.

When the KVM CPU capabilities are queried and modified, a CPUID
overlay is used according to the VM type and/or the hardware platform.

For ALIASED_1_EDX_F() use CPUID_OL_SVM instead of CPUID_OL_DEFAULT, since
the aliased 0x8000_0001.EDX features are AMD-defined duplicates of 0x1.EDX
and are only meaningful for SVM guests.

Drop the now-unnecessary CPUID_OL_DEFAULT alias.

Return 0 for emulated CPUIDs when the overlay is TDX, as KVM cannot
emulate the related instruction for TDX guests.

Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
---
 arch/x86/kvm/cpuid.c | 19 ++++++++++++-------
 arch/x86/kvm/cpuid.h |  9 ++++-----
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 20ea483ddc7a..2c4e64aa14c4 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -374,6 +374,7 @@ static int cpuid_func_emulated(struct kvm *kvm, struct kvm_cpuid_entry2 *entry,
 
 void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
+	u8 cpuid_overlay = get_cpuid_overlay(vcpu->kvm);
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	struct kvm_cpuid_entry2 *best;
 	struct kvm_cpuid_entry2 *entry;
@@ -404,7 +405,7 @@ void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 		 * in guest CPUID.  Note, this includes features that are
 		 * supported by KVM but aren't advertised to userspace!
 		 */
-		vcpu->arch.cpu_caps[i] = kvm_cpu_caps[CPUID_OL_DEFAULT][i];
+		vcpu->arch.cpu_caps[i] = kvm_cpu_caps[cpuid_overlay][i];
 		if (!cpuid.index) {
 			cpuid_func_emulated(vcpu->kvm, &emulated, cpuid.function, true);
 			vcpu->arch.cpu_caps[i] |= cpuid_get_reg_unsafe(&emulated, cpuid.reg);
@@ -806,12 +807,12 @@ do {									\
  * Aliased Features - For features in 0x8000_0001.EDX that are duplicates of
  * identical 0x1.EDX features, and thus are aliased from 0x1 to 0x8000_0001.
  */
-#define ALIASED_1_EDX_F(name)								\
-({											\
-	BUILD_BUG_ON(__feature_leaf(X86_FEATURE_##name) != CPUID_1_EDX);		\
-	BUILD_BUG_ON(kvm_cpu_cap_init_in_progress != CPUID_8000_0001_EDX);		\
-	kvm_cpu_cap_features |= feature_bit(name);					\
-	kvm_cpu_caps[CPUID_OL_DEFAULT][CPUID_8000_0001_EDX] |= feature_bit(name);	\
+#define ALIASED_1_EDX_F(name)							\
+({										\
+	BUILD_BUG_ON(__feature_leaf(X86_FEATURE_##name) != CPUID_1_EDX);	\
+	BUILD_BUG_ON(kvm_cpu_cap_init_in_progress != CPUID_8000_0001_EDX);	\
+	kvm_cpu_cap_features |= feature_bit(name);				\
+	kvm_cpu_caps[CPUID_OL_SVM][CPUID_8000_0001_EDX] |= feature_bit(name);	\
 })
 
 /*
@@ -1414,6 +1415,10 @@ static int cpuid_func_emulated(struct kvm *kvm, struct kvm_cpuid_entry2 *entry,
 	entry->index = 0;
 	entry->flags = 0;
 
+	/* KVM can't do the following emulations for TDX guests. */
+	if (get_cpuid_overlay(kvm) == CPUID_OL_TDX)
+		return 0;
+
 	switch (func) {
 	case 0:
 		entry->eax = 7;
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index eae46f37d30f..c3f2417c7980 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -14,9 +14,6 @@ enum kvm_cpuid_overlay {
 	NR_CPUID_OL
 };
 
-/* Temporarily use VMX overlay as the default one */
-#define CPUID_OL_DEFAULT	CPUID_OL_VMX
-
 #define F_CPUID_VMX		BIT(CPUID_OL_VMX)
 #define F_CPUID_SVM		BIT(CPUID_OL_SVM)
 #define F_CPUID_TDX		BIT(CPUID_OL_TDX)
@@ -122,9 +119,10 @@ static __always_inline void cpuid_entry_override(struct kvm *kvm,
 						 unsigned int leaf)
 {
 	u32 *reg = cpuid_entry_get_reg(entry, leaf * 32);
+	u8 cpuid_overlay = get_cpuid_overlay(kvm);
 
 	BUILD_BUG_ON(leaf >= ARRAY_SIZE(kvm_cpu_caps[0]));
-	*reg = kvm_cpu_caps[CPUID_OL_DEFAULT][leaf];
+	*reg = kvm_cpu_caps[cpuid_overlay][leaf];
 }
 
 static __always_inline bool guest_cpuid_has(struct kvm_vcpu *vcpu,
@@ -245,8 +243,9 @@ static __always_inline void kvm_cpu_cap_set(unsigned int x86_feature, u32 overla
 static __always_inline u32 kvm_cpu_cap_get(struct kvm *kvm, unsigned int x86_feature)
 {
 	unsigned int x86_leaf = __feature_leaf(x86_feature);
+	u8 cpuid_overlay = get_cpuid_overlay(kvm);
 
-	return kvm_cpu_caps[CPUID_OL_DEFAULT][x86_leaf] & __feature_bit(x86_feature);
+	return kvm_cpu_caps[cpuid_overlay][x86_leaf] & __feature_bit(x86_feature);
 }
 
 static __always_inline bool kvm_cpu_cap_has(struct kvm *kvm, unsigned int x86_feature)
-- 
2.46.0