KVM: x86: Add a helper to check for a legal GPA

Add a helper to check for a legal GPA, and use it to consolidate code
in existing, related helpers.  Future patches will extend usage to
VMX and SVM code, properly handle exceptions to the maxphyaddr rule, and
add more helpers.

No functional change intended.
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210204000117.3303214-4-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/cpuid.h

@@ -36,9 +36,19 @@ static inline int cpuid_maxphyaddr(struct kvm_vcpu *vcpu)
 	return vcpu->arch.maxphyaddr;
 }
 
+static inline bool kvm_vcpu_is_legal_gpa(struct kvm_vcpu *vcpu, gpa_t gpa)
+{
+	return !(gpa >> cpuid_maxphyaddr(vcpu));
+}
+
 static inline bool kvm_vcpu_is_illegal_gpa(struct kvm_vcpu *vcpu, gpa_t gpa)
 {
-	return (gpa >= BIT_ULL(cpuid_maxphyaddr(vcpu)));
+	return !kvm_vcpu_is_legal_gpa(vcpu, gpa);
+}
+
+static inline bool page_address_valid(struct kvm_vcpu *vcpu, gpa_t gpa)
+{
+	return PAGE_ALIGNED(gpa) && kvm_vcpu_is_legal_gpa(vcpu, gpa);
 }
 
 struct cpuid_reg {
@@ -324,11 +334,6 @@ static __always_inline void kvm_cpu_cap_check_and_set(unsigned int x86_feature)
 		kvm_cpu_cap_set(x86_feature);
 }
 
-static inline bool page_address_valid(struct kvm_vcpu *vcpu, gpa_t gpa)
-{
-	return PAGE_ALIGNED(gpa) && !(gpa >> cpuid_maxphyaddr(vcpu));
-}
-
 static __always_inline bool guest_pv_has(struct kvm_vcpu *vcpu,
 					 unsigned int kvm_feature)
 {