KVM: PPC: Book3S HV: Create kvmppc_unmap_hpte_helper()

The kvm_unmap_rmapp() function, called from certain MMU notifiers, is used
to force all guest mappings of a particular host page to be set ABSENT, and
removed from the reverse mappings.

For HPT resizing, we will have some cases where we want to set just a
single guest HPTE ABSENT and remove its reverse mappings.  To prepare with
this, we split out the logic from kvm_unmap_rmapp() to evict a single HPTE,
moving it to a new helper function.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -742,37 +742,15 @@ static int kvm_handle_hva(struct kvm *kvm, unsigned long hva,
 	return kvm_handle_hva_range(kvm, hva, hva + 1, handler);
 }
 
-static int kvm_unmap_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot,
-			   unsigned long gfn)
+/* Must be called with both HPTE and rmap locked */
+static void kvmppc_unmap_hpte(struct kvm *kvm, unsigned long i,
+			      unsigned long *rmapp, unsigned long gfn)
 {
+	__be64 *hptep = (__be64 *) (kvm->arch.hpt.virt + (i << 4));
 	struct revmap_entry *rev = kvm->arch.hpt.rev;
-	unsigned long h, i, j;
-	__be64 *hptep;
+	unsigned long j, h;
 	unsigned long ptel, psize, rcbits;
-	unsigned long *rmapp;
 
-	rmapp = &memslot->arch.rmap[gfn - memslot->base_gfn];
-	for (;;) {
-		lock_rmap(rmapp);
-		if (!(*rmapp & KVMPPC_RMAP_PRESENT)) {
-			unlock_rmap(rmapp);
-			break;
-		}
-
-		/*
-		 * To avoid an ABBA deadlock with the HPTE lock bit,
-		 * we can't spin on the HPTE lock while holding the
-		 * rmap chain lock.
-		 */
-		i = *rmapp & KVMPPC_RMAP_INDEX;
-		hptep = (__be64 *) (kvm->arch.hpt.virt + (i << 4));
-		if (!try_lock_hpte(hptep, HPTE_V_HVLOCK)) {
-			/* unlock rmap before spinning on the HPTE lock */
-			unlock_rmap(rmapp);
-			while (be64_to_cpu(hptep[0]) & HPTE_V_HVLOCK)
-				cpu_relax();
-			continue;
-		}
 	j = rev[i].forw;
 	if (j == i) {
 		/* chain is now empty */
@@ -804,6 +782,39 @@ static int kvm_unmap_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot,
 			note_hpte_modification(kvm, &rev[i]);
 		}
 	}
+}
+
+static int kvm_unmap_rmapp(struct kvm *kvm, struct kvm_memory_slot *memslot,
+			   unsigned long gfn)
+{
+	unsigned long i;
+	__be64 *hptep;
+	unsigned long *rmapp;
+
+	rmapp = &memslot->arch.rmap[gfn - memslot->base_gfn];
+	for (;;) {
+		lock_rmap(rmapp);
+		if (!(*rmapp & KVMPPC_RMAP_PRESENT)) {
+			unlock_rmap(rmapp);
+			break;
+		}
+
+		/*
+		 * To avoid an ABBA deadlock with the HPTE lock bit,
+		 * we can't spin on the HPTE lock while holding the
+		 * rmap chain lock.
+		 */
+		i = *rmapp & KVMPPC_RMAP_INDEX;
+		hptep = (__be64 *) (kvm->arch.hpt.virt + (i << 4));
+		if (!try_lock_hpte(hptep, HPTE_V_HVLOCK)) {
+			/* unlock rmap before spinning on the HPTE lock */
+			unlock_rmap(rmapp);
+			while (be64_to_cpu(hptep[0]) & HPTE_V_HVLOCK)
+				cpu_relax();
+			continue;
+		}
+
+		kvmppc_unmap_hpte(kvm, i, rmapp, gfn);
 		unlock_rmap(rmapp);
 		__unlock_hpte(hptep, be64_to_cpu(hptep[0]));
 	}