linux-kernel - [PATCH 3.10 242/250] kvm: exclude ioeventfd from counting kvm_io

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Date:   Thu,  8 Jun 2017 01:00:28 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Amos Kong <akong@...hat.com>, Gleb Natapov <gleb@...hat.com>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 242/250] kvm: exclude ioeventfd from counting kvm_io_range limit

From: Amos Kong <akong@...hat.com>

commit 6ea34c9b78c10289846db0abeebd6b84d5aca084 upstream.

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 <akong@...hat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@...hat.com>
Signed-off-by: Gleb Natapov <gleb@...hat.com>
[wt: next patch depends on this one]
Signed-off-by: Willy Tarreau <w@....eu>
---
 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 8db53cf..cbe9083 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -145,7 +145,8 @@ 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 e9128725..36d14e5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2936,7 +2936,8 @@ 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) *
-- 
2.8.0.rc2.1.gbe9624a