KVM: x86/mmu: Don't try to unprotect an INVALID_GPA

If getting the gpa for a gva fails, e.g. because the gva isn't mapped in
the guest page tables, don't try to unprotect the invalid gfn.  This is
mostly a performance fix (avoids unnecessarily taking mmu_lock), as
for_each_gfn_valid_sp_with_gptes() won't explode on garbage input, it's
simply pointless.

Link: https://lore.kernel.org/r/20240831001538.336683-13-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/mmu/mmu.c

@@ -2729,8 +2729,11 @@ bool kvm_mmu_unprotect_gfn_and_retry(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa)
 	if (!READ_ONCE(vcpu->kvm->arch.indirect_shadow_pages))
 		return false;
 
-	if (!vcpu->arch.mmu->root_role.direct)
+	if (!vcpu->arch.mmu->root_role.direct) {
 		gpa = kvm_mmu_gva_to_gpa_write(vcpu, cr2_or_gpa, NULL);
+		if (gpa == INVALID_GPA)
+			return false;
+	}
 
 	r = kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa));
 	if (r) {
@@ -2749,6 +2752,8 @@ static int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva)
 		return 0;
 
 	gpa = kvm_mmu_gva_to_gpa_read(vcpu, gva, NULL);
+	if (gpa == INVALID_GPA)
+		return 0;
 
 	r = kvm_mmu_unprotect_page(vcpu->kvm, gpa >> PAGE_SHIFT);