linux-kernel - [87/98] KVM: only allow one gsi per fd

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Date:	Tue, 26 Jan 2010 15:34:53 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	"Michael S. Tsirkin" <mst@...hat.com>,
	"Acked-by: Gregory Haskins" <ghaskins@...ell.com>,
	Avi Kivity <avi@...hat.com>
Subject: [87/98] KVM: only allow one gsi per fd

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Michael S. Tsirkin <mst@...hat.com>

commit f1d1c309f35e9b0fb961cffd70fbd04f450ec47c upstream.

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
storm 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@...hat.com>
Acked-by: Acked-by: Gregory Haskins <ghaskins@...ell.com>
Signed-off-by: Avi Kivity <avi@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

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

--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -168,7 +168,7 @@ irqfd_ptable_queue_proc(struct file *fil
 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;
@@ -205,9 +205,20 @@ kvm_irqfd_assign(struct kvm *kvm, int fd
 	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);
 	spin_unlock_irq(&kvm->irqfds.lock);
 


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