Third set of PPC KVM fixes for 4.19

One patch here, fixing a potential host crash introduced (or at least
 exacerbated) by a previous fix for corruption relating to radix guest
 page faults and THP operations.
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Merge tag 'kvm-ppc-fixes-4.19-3' of git://git.kernel.org/pub/scm/linux/kernel/git/paulus/powerpc into kvm-master

Third set of PPC KVM fixes for 4.19

One patch here, fixing a potential host crash introduced (or at least
exacerbated) by a previous fix for corruption relating to radix guest
page faults and THP operations.

arch/powerpc/kvm/book3s_64_mmu_radix.c

@@ -646,6 +646,16 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	 */
 	local_irq_disable();
 	ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift);
+	/*
+	 * If the PTE disappeared temporarily due to a THP
+	 * collapse, just return and let the guest try again.
+	 */
+	if (!ptep) {
+		local_irq_enable();
+		if (page)
+			put_page(page);
+		return RESUME_GUEST;
+	}
 	pte = *ptep;
 	local_irq_enable();