KVM: x86: Add a helper to query whether or not a vCPU has ever run

Add a helper to query if a vCPU has run so that KVM doesn't have to open
code the check on last_vmentry_cpu being set to a magic value.

No functional change intended.
Suggested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Cc: Like Xu <like.xu.linux@gmail.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20230311004618.920745-3-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/cpuid.c

@@ -420,7 +420,7 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
 	 * KVM_SET_CPUID{,2} again. To support this legacy behavior, check
 	 * whether the supplied CPUID data is equal to what's already set.
 	 */
-	if (vcpu->arch.last_vmentry_cpu != -1) {
+	if (kvm_vcpu_has_run(vcpu)) {
 		r = kvm_cpuid_check_equal(vcpu, e2, nent);
 		if (r)
 			return r;

arch/x86/kvm/mmu/mmu.c

@@ -5393,7 +5393,7 @@ void kvm_mmu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	 * Changing guest CPUID after KVM_RUN is forbidden, see the comment in
 	 * kvm_arch_vcpu_ioctl().
 	 */
-	KVM_BUG_ON(vcpu->arch.last_vmentry_cpu != -1, vcpu->kvm);
+	KVM_BUG_ON(kvm_vcpu_has_run(vcpu), vcpu->kvm);
 }
 
 void kvm_mmu_reset_context(struct kvm_vcpu *vcpu)

arch/x86/kvm/x86.h

@@ -83,6 +83,11 @@ static inline unsigned int __shrink_ple_window(unsigned int val,
 void kvm_service_local_tlb_flush_requests(struct kvm_vcpu *vcpu);
 int kvm_check_nested_events(struct kvm_vcpu *vcpu);
 
+static inline bool kvm_vcpu_has_run(struct kvm_vcpu *vcpu)
+{
+	return vcpu->arch.last_vmentry_cpu != -1;
+}
+
 static inline bool kvm_is_exception_pending(struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.exception.pending ||