KVM: PPC: NULL return of kvmppc_mmu_hpte_cache_next should be handled

NULL return of kvmppc_mmu_hpte_cache_next should be handled
Signed-off-by: Zhouyi Zhou <yizhouzhou@ict.ac.cn>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_32_mmu_host.c

@@ -243,6 +243,11 @@ int kvmppc_mmu_map_page(struct kvm_vcpu *vcpu, struct kvmppc_pte *orig_pte,
 	/* Now tell our Shadow PTE code about the new page */
 
 	pte = kvmppc_mmu_hpte_cache_next(vcpu);
+	if (!pte) {
+		kvm_release_pfn_clean(hpaddr >> PAGE_SHIFT);
+		r = -EAGAIN;
+		goto out;
+	}
 
 	dprintk_mmu("KVM: %c%c Map 0x%llx: [%lx] 0x%llx (0x%llx) -> %lx\n",
 		    orig_pte->may_write ? 'w' : '-',