[Qemu-devel] [PATCH] kvm: exclude ioeventfd from counting kvm_io_range limit

[Amos Kong]

We can easily reach the 1000 limit by start VM with a couple
hundred I/O devices (multifunction=on). The hardcode limit
already been adjusted 3 times (6 ~ 200 ~ 300 ~ 1000).

In userspace, we already have maximum file descriptor to
limit ioeventfd count. But kvm_io_bus devices also are used
for pit, pic, ioapic, coalesced_mmio. They couldn't be limited
by maximum file descriptor.

Currently only ioeventfds take too much kvm_io_bus devices,
so just exclude it from counting kvm_io_range limit.

Also fixed one indent issue in kvm_host.h

Signed-off-by: Amos Kong <address@hidden>
---
 include/linux/kvm_host.h | 3 ++-
 virt/kvm/eventfd.c       | 2 ++
 virt/kvm/kvm_main.c      | 3 ++-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f0eea07..ef261ab 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -144,7 +144,8 @@ struct kvm_io_range {
 #define NR_IOBUS_DEVS 1000
 
 struct kvm_io_bus {
-       int                   dev_count;
+       int dev_count;
+       int ioeventfd_count;
        struct kvm_io_range range[];
 };
 
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 64ee720..1550637 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -753,6 +753,7 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd 
*args)
        if (ret < 0)
                goto unlock_fail;
 
+       kvm->buses[bus_idx]->ioeventfd_count++;
        list_add_tail(&p->list, &kvm->ioeventfds);
 
        mutex_unlock(&kvm->slots_lock);
@@ -798,6 +799,7 @@ kvm_deassign_ioeventfd(struct kvm *kvm, struct 
kvm_ioeventfd *args)
                        continue;
 
                kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev);
+               kvm->buses[bus_idx]->ioeventfd_count--;
                ioeventfd_release(p);
                ret = 0;
                break;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 302681c..c6d9baf 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2926,7 +2926,8 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus 
bus_idx, gpa_t addr,
        struct kvm_io_bus *new_bus, *bus;
 
        bus = kvm->buses[bus_idx];
-       if (bus->dev_count > NR_IOBUS_DEVS - 1)
+       /* exclude ioeventfd which is limited by maximum fd */
+       if (bus->dev_count - bus->ioeventfd_count > NR_IOBUS_DEVS - 1)
                return -ENOSPC;
 
        new_bus = kzalloc(sizeof(*bus) + ((bus->dev_count + 1) *
-- 
1.8.1.4