KVM: selftests: Add helpers to get and modify a vCPU's CPUID entries

Add helpers to get a specific CPUID entry for a given vCPU, and to toggle
a specific CPUID-based feature for a vCPU.  The helpers will reduce the
amount of boilerplate code needed to tweak a vCPU's CPUID model, improve
code clarity, and most importantly move tests away from modifying the
static "cpuid" returned by kvm_get_supported_cpuid().
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-23-seanjc@google.com

tools/testing/selftests/kvm/include/x86_64/processor.h

@@ -622,6 +622,19 @@ struct kvm_cpuid_entry2 *get_cpuid_entry(struct kvm_cpuid2 *cpuid,
 					 uint32_t function, uint32_t index);
 void vcpu_init_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid);
 
+static inline struct kvm_cpuid_entry2 *__vcpu_get_cpuid_entry(struct kvm_vcpu *vcpu,
+							      uint32_t function,
+							      uint32_t index)
+{
+	return get_cpuid_entry(vcpu->cpuid, function, index);
+}
+
+static inline struct kvm_cpuid_entry2 *vcpu_get_cpuid_entry(struct kvm_vcpu *vcpu,
+							    uint32_t function)
+{
+	return __vcpu_get_cpuid_entry(vcpu, function, 0);
+}
+
 static inline int __vcpu_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	int r;
@@ -645,6 +658,23 @@ static inline void vcpu_set_cpuid(struct kvm_vcpu *vcpu)
 	vcpu_ioctl(vcpu, KVM_GET_CPUID2, vcpu->cpuid);
 }
 
+void vcpu_set_or_clear_cpuid_feature(struct kvm_vcpu *vcpu,
+				     struct kvm_x86_cpu_feature feature,
+				     bool set);
+
+static inline void vcpu_set_cpuid_feature(struct kvm_vcpu *vcpu,
+					  struct kvm_x86_cpu_feature feature)
+{
+	vcpu_set_or_clear_cpuid_feature(vcpu, feature, true);
+
+}
+
+static inline void vcpu_clear_cpuid_feature(struct kvm_vcpu *vcpu,
+					    struct kvm_x86_cpu_feature feature)
+{
+	vcpu_set_or_clear_cpuid_feature(vcpu, feature, false);
+}
+
 static inline struct kvm_cpuid_entry2 *kvm_get_supported_cpuid_index(uint32_t function,
 								     uint32_t index)
 {

tools/testing/selftests/kvm/lib/x86_64/processor.c

@@ -766,6 +766,24 @@ void vcpu_init_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid)
 	vcpu_set_cpuid(vcpu);
 }
 
+void vcpu_set_or_clear_cpuid_feature(struct kvm_vcpu *vcpu,
+				     struct kvm_x86_cpu_feature feature,
+				     bool set)
+{
+	struct kvm_cpuid_entry2 *entry;
+	u32 *reg;
+
+	entry = __vcpu_get_cpuid_entry(vcpu, feature.function, feature.index);
+	reg = (&entry->eax) + feature.reg;
+
+	if (set)
+		*reg |= BIT(feature.bit);
+	else
+		*reg &= ~BIT(feature.bit);
+
+	vcpu_set_cpuid(vcpu);
+}
+
 uint64_t vcpu_get_msr(struct kvm_vcpu *vcpu, uint64_t msr_index)
 {
 	struct {