KVM: x86: avoid logical_map when it is invalid

We want to support mixed modes and the easiest solution is to avoid
optimizing those weird and unlikely scenarios.
Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>
Message-Id: <1423766494-26150-4-git-send-email-rkrcmar@redhat.com>
[Add comment above KVM_APIC_MODE_* defines. - Paolo]
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -548,8 +548,20 @@ struct kvm_arch_memory_slot {
 	struct kvm_lpage_info *lpage_info[KVM_NR_PAGE_SIZES - 1];
 };
 
+/*
+ * We use as the mode the number of bits allocated in the LDR for the
+ * logical processor ID.  It happens that these are all powers of two.
+ * This makes it is very easy to detect cases where the APICs are
+ * configured for multiple modes; in that case, we cannot use the map and
+ * hence cannot use kvm_irq_delivery_to_apic_fast either.
+ */
+#define KVM_APIC_MODE_XAPIC_CLUSTER          4
+#define KVM_APIC_MODE_XAPIC_FLAT             8
+#define KVM_APIC_MODE_X2APIC                16
+
 struct kvm_apic_map {
 	struct rcu_head rcu;
+	u8 mode;
 	u8 ldr_bits;
 	/* fields bellow are used to decode ldr values in different modes */
 	u32 cid_shift, cid_mask, lid_mask;

arch/x86/kvm/lapic.c

@@ -133,6 +133,14 @@ static inline int kvm_apic_id(struct kvm_lapic *apic)
 	return (kvm_apic_get_reg(apic, APIC_ID) >> 24) & 0xff;
 }
 
+/* The logical map is definitely wrong if we have multiple
+ * modes at the same time.  (Physical map is always right.)
+ */
+static inline bool kvm_apic_logical_map_valid(struct kvm_apic_map *map)
+{
+	return !(map->mode & (map->mode - 1));
+}
+
 static void recalculate_apic_map(struct kvm *kvm)
 {
 	struct kvm_apic_map *new, *old = NULL;
@@ -162,16 +170,19 @@ static void recalculate_apic_map(struct kvm *kvm)
 			new->ldr_bits = 32;
 			new->cid_shift = 16;
 			new->cid_mask = new->lid_mask = 0xffff;
+			new->mode |= KVM_APIC_MODE_X2APIC;
 		} else if (kvm_apic_get_reg(apic, APIC_LDR)) {
 			if (kvm_apic_get_reg(apic, APIC_DFR) ==
 							APIC_DFR_CLUSTER) {
 				new->cid_shift = 4;
 				new->cid_mask = 0xf;
 				new->lid_mask = 0xf;
+				new->mode |= KVM_APIC_MODE_XAPIC_CLUSTER;
 			} else {
 				new->cid_shift = 8;
 				new->cid_mask = 0;
 				new->lid_mask = 0xff;
+				new->mode |= KVM_APIC_MODE_XAPIC_FLAT;
 			}
 		}
 
@@ -201,6 +212,10 @@ static void recalculate_apic_map(struct kvm *kvm)
 
 		if (aid < ARRAY_SIZE(new->phys_map))
 			new->phys_map[aid] = apic;
+
+		if (!kvm_apic_logical_map_valid(new));
+			continue;
+
 		if (lid && cid < ARRAY_SIZE(new->logical_map))
 			new->logical_map[cid][ffs(lid) - 1] = apic;
 	}
@@ -718,7 +733,14 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
 		dst = &map->phys_map[irq->dest_id];
 	} else {
 		u32 mda = irq->dest_id << (32 - map->ldr_bits);
-		u16 cid = apic_cluster_id(map, mda);
+		u16 cid;
+
+		if (!kvm_apic_logical_map_valid(map)) {
+			ret = false;
+			goto out;
+		}
+
+		cid = apic_cluster_id(map, mda);
 
 		if (cid >= ARRAY_SIZE(map->logical_map))
 			goto out;