kvm: irqchip: Break up high order allocations of kvm_irq_routing_table

The allocation size of the kvm_irq_routing_table depends on
the number of irq routing entries because they are all
allocated with one kzalloc call.

When the irq routing table gets bigger this requires high
order allocations which fail from time to time:

	qemu-kvm: page allocation failure: order:4, mode:0xd0

This patch fixes this issue by breaking up the allocation of
the table and its entries into individual kzalloc calls.
These could all be satisfied with order-0 allocations, which
are less likely to fail.

The downside of this change is the lower performance, because
of more calls to kzalloc. But given how often kvm_set_irq_routing
is called in the lifetime of a guest, it doesn't really
matter much.
Signed-off-by: NJoerg Roedel <jroedel@suse.de>
[Avoid sparse warning through rcu_access_pointer. - Paolo]
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

virt/kvm/irqchip.c

@@ -33,7 +33,6 @@
 
 struct kvm_irq_routing_table {
 	int chip[KVM_NR_IRQCHIPS][KVM_IRQCHIP_NUM_PINS];
-	struct kvm_kernel_irq_routing_entry *rt_entries;
 	u32 nr_rt_entries;
 	/*
 	 * Array indexed by gsi. Each entry contains list of irq chips
@@ -118,11 +117,32 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
 	return ret;
 }
 
+static void free_irq_routing_table(struct kvm_irq_routing_table *rt)
+{
+	int i;
+
+	if (!rt)
+		return;
+
+	for (i = 0; i < rt->nr_rt_entries; ++i) {
+		struct kvm_kernel_irq_routing_entry *e;
+		struct hlist_node *n;
+
+		hlist_for_each_entry_safe(e, n, &rt->map[i], link) {
+			hlist_del(&e->link);
+			kfree(e);
+		}
+	}
+
+	kfree(rt);
+}
+
 void kvm_free_irq_routing(struct kvm *kvm)
 {
 	/* Called only during vm destruction. Nobody can use the pointer
 	   at this stage */
-	kfree(kvm->irq_routing);
+	struct kvm_irq_routing_table *rt = rcu_access_pointer(kvm->irq_routing);
+	free_irq_routing_table(rt);
 }
 
 static int setup_routing_entry(struct kvm_irq_routing_table *rt,
@@ -173,25 +193,29 @@ int kvm_set_irq_routing(struct kvm *kvm,
 
 	nr_rt_entries += 1;
 
-	new = kzalloc(sizeof(*new) + (nr_rt_entries * sizeof(struct hlist_head))
-		      + (nr * sizeof(struct kvm_kernel_irq_routing_entry)),
+	new = kzalloc(sizeof(*new) + (nr_rt_entries * sizeof(struct hlist_head)),
 		      GFP_KERNEL);
 
 	if (!new)
 		return -ENOMEM;
 
-	new->rt_entries = (void *)&new->map[nr_rt_entries];
-
 	new->nr_rt_entries = nr_rt_entries;
 	for (i = 0; i < KVM_NR_IRQCHIPS; i++)
 		for (j = 0; j < KVM_IRQCHIP_NUM_PINS; j++)
 			new->chip[i][j] = -1;
 
 	for (i = 0; i < nr; ++i) {
+		struct kvm_kernel_irq_routing_entry *e;
+
+		r = -ENOMEM;
+		e = kzalloc(sizeof(*e), GFP_KERNEL);
+		if (!e)
+			goto out;
+
 		r = -EINVAL;
 		if (ue->flags)
 			goto out;
-		r = setup_routing_entry(new, &new->rt_entries[i], ue);
+		r = setup_routing_entry(new, e, ue);
 		if (r)
 			goto out;
 		++ue;
@@ -209,6 +233,7 @@ int kvm_set_irq_routing(struct kvm *kvm,
 	r = 0;
 
 out:
-	kfree(new);
+	free_irq_routing_table(new);
+
 	return r;
 }