linux-kernel - [PATCH 3.10 120/180] kvm: Fix irq route entries exceeding KVM_MAX_IRQ

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Message-Id: <1471793510-13022-121-git-send-email-w@1wt.eu>
Date:   Sun, 21 Aug 2016 17:30:50 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Xiubo Li <lixiubo@...s.chinamobile.com>,
        Wei Tang <tangwei@...s.chinamobile.com>,
        Zhang Zhuoyu <zhangzhuoyu@...s.chinamobile.com>,
        Paolo Bonzini <pbonzini@...hat.com>, Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 120/180] kvm: Fix irq route entries exceeding KVM_MAX_IRQ_ROUTES

From: Xiubo Li <lixiubo@...s.chinamobile.com>

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:

irq_affinity.sh
========================================================================

vda_irq_num=25
vdb_irq_num=27
while [ 1 ]
do
    for irq in {1,2,4,8,10,20,40,80}
        do
            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
        done
done
========================================================================

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.

Cc: stable@...r.kernel.org
Signed-off-by: Xiubo Li <lixiubo@...s.chinamobile.com>
Signed-off-by: Wei Tang <tangwei@...s.chinamobile.com>
Signed-off-by: Zhang Zhuoyu <zhangzhuoyu@...s.chinamobile.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Willy Tarreau <w@....eu>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4f865e1..f71c4ad 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2447,7 +2447,7 @@ static long kvm_vm_ioctl(struct file *filp,
 		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;
-- 
2.8.0.rc2.1.gbe9624a