ANDROID: KVM: arm64: Avoid unnecessary unmap walk in MEM_RELINQUISH hypercall

If the mapping is determined to be not present in an earlier walk,
attempting the unmap is pointless.

Bug: 357781595
Change-Id: I6fd939556b80d7a9a0731cab36166a652f7a7c6d
Signed-off-by: Keir Fraser <keirf@google.com>

arch/arm64/kvm/hyp/nvhe/mem_protect.c

@@ -378,7 +378,7 @@ int __pkvm_guest_relinquish_to_host(struct pkvm_hyp_vcpu *vcpu,
 	ret = kvm_pgtable_walk(&vm->pgt, ipa, PAGE_SIZE, &walker);
 
 	/* Zap the guest stage2 pte. */
-	if (!ret)
+	if (!ret && data.pa)
 		kvm_pgtable_stage2_unmap(&vm->pgt, ipa, PAGE_SIZE);
 
 	guest_unlock_component(vm);