[PATCH] kvm: only allow one gsi per fd

From: Michael S. Tsirkin
Date: Wed Jan 13 2010 - 12:01:22 EST

Looks like repeatedly binding same fd to multiple gsi's with irqfd can
use up a ton of kernel memory for irqfd structures.

A simple fix is to allow each fd to only trigger one gsi: triggering a
srorm of interrupts in guest is likely useless anyway, and we can do it
by binding a single gsi to many interrupts if we really want to.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

This patch is IMO a good candidate for 2.6.33 and 2.6.32.x.

virt/kvm/eventfd.c | 15 +++++++++++++--
1 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 30f70fd..62e4cd9 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -166,7 +166,7 @@ irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
static int
kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
- struct _irqfd *irqfd;
+ struct _irqfd *irqfd, *tmp;
struct file *file = NULL;
struct eventfd_ctx *eventfd = NULL;
int ret;
@@ -203,9 +203,20 @@ kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
init_poll_funcptr(&irqfd->pt, irqfd_ptable_queue_proc);

+ spin_lock_irq(&kvm->irqfds.lock);
+ ret = 0;
+ list_for_each_entry(tmp, &kvm->irqfds.items, list) {
+ if (irqfd->eventfd != tmp->eventfd)
+ continue;
+ /* This fd is used for another irq already. */
+ ret = -EBUSY;
+ spin_unlock_irq(&kvm->irqfds.lock);
+ goto fail;
+ }
events = file->f_op->poll(file, &irqfd->pt);

- spin_lock_irq(&kvm->irqfds.lock);
list_add_tail(&irqfd->list, &kvm->irqfds.items);

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