[RFC v3 5/5] KVM: enforce NR_IOBUS_DEVS limit if kmemcg is disabled

[Elena Afanasova <eafanasova@gmail.com>]

ioregionfd relies on kmemcg in order to limit the amount of kernel memory
that userspace can consume. Enforce NR_IOBUS_DEVS hardcoded limit in case
kmemcg is disabled.

Signed-off-by: Elena Afanasova <eafanasova@gmail.com>
---
 virt/kvm/kvm_main.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index df387857f51f..99a828153afd 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4320,9 +4320,12 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 	if (!bus)
 		return -ENOMEM;
 
-	/* exclude ioeventfd which is limited by maximum fd */
-	if (bus->dev_count - bus->ioeventfd_count > NR_IOBUS_DEVS - 1)
-		return -ENOSPC;
+	/* enforce hard limit if kmemcg is disabled and
+	 * exclude ioeventfd which is limited by maximum fd
+	 */
+	if (!memcg_kmem_enabled())
+		if (bus->dev_count - bus->ioeventfd_count > NR_IOBUS_DEVS - 1)
+			return -ENOSPC;
 
 	new_bus = kmalloc(struct_size(bus, range, bus->dev_count + 1),
 			  GFP_KERNEL_ACCOUNT);
-- 
2.25.1