[PATCH 4.6 078/203] kvm: Fix irq route entries exceeding KVM_MAX_IRQ_ROUTES

From: Greg Kroah-Hartman
Date: Mon Jul 25 2016 - 18:14:59 EST

4.6-stable review patch. If anyone has any objections, please let me know.


From: Xiubo Li <lixiubo@xxxxxxxxxxxxxxxxxxxx>

commit caf1ff26e1aa178133df68ac3d40815fed2187d9 upstream.

These days, we experienced one guest crash with 8 cores and 3 disks,
with qemu error logs as bellow:

qemu-system-x86_64: /build/qemu-2.0.0/kvm-all.c:984:
kvm_irqchip_commit_routes: Assertion `ret == 0' failed.

And then we found one patch(bdf026317d) in qemu tree, which said
could fix this bug.

Execute the following script will reproduce the BUG quickly:


while [ 1 ]
for irq in {1,2,4,8,10,20,40,80}
echo $irq > /proc/irq/$vda_irq_num/smp_affinity
echo $irq > /proc/irq/$vdb_irq_num/smp_affinity
dd if=/dev/vda of=/dev/zero bs=4K count=100 iflag=direct
dd if=/dev/vdb of=/dev/zero bs=4K count=100 iflag=direct

The following qemu log is added in the qemu code and is displayed when
this bug reproduced:

kvm_irqchip_commit_routes: max gsi: 1008, nr_allocated_irq_routes: 1024,
irq_routes->nr: 1024, gsi_count: 1024.

That's to say when irq_routes->nr == 1024, there are 1024 routing entries,
but in the kernel code when routes->nr >= 1024, will just return -EINVAL;

The nr is the number of the routing entries which is in of
[1 ~ KVM_MAX_IRQ_ROUTES], not the index in [0 ~ KVM_MAX_IRQ_ROUTES - 1].

This patch fix the BUG above.

Signed-off-by: Xiubo Li <lixiubo@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Wei Tang <tangwei@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Zhang Zhuoyu <zhangzhuoyu@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

virt/kvm/kvm_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2868,7 +2868,7 @@ static long kvm_vm_ioctl(struct file *fi
if (copy_from_user(&routing, argp, sizeof(routing)))
goto out;
r = -EINVAL;
- if (routing.nr >= KVM_MAX_IRQ_ROUTES)
+ if (routing.nr > KVM_MAX_IRQ_ROUTES)
goto out;
if (routing.flags)
goto out;