[v2.6.34-stable 66/77] KVM: x86: Prevent starting PIT timers in the absence of irqchip support

Paul Gortmaker
2013-01-08T23:39:51Z

From: Jan Kiszka <jan.kiszka@siemens.com>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
If you see a problem with using this for longterm, please comment.
-------------------

commit 0924ab2cfa98b1ece26c033d696651fd62896c69 upstream.

User space may create the PIT and forgets about setting up the irqchips.
In that case, firing PIT IRQs will crash the host:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000128
IP: [<ffffffffa10f6280>] kvm_set_irq+0x30/0x170 [kvm]
...
Call Trace:
[<ffffffffa11228c1>] pit_do_work+0x51/0xd0 [kvm]
[<ffffffff81071431>] process_one_work+0x111/0x4d0
[<ffffffff81071bb2>] worker_thread+0x152/0x340
[<ffffffff81075c8e>] kthread+0x7e/0x90
[<ffffffff815a4474>] kernel_thread_helper+0x4/0x10

Prevent this by checking the irqchip mode before starting a timer. We
can't deny creating the PIT if the irqchips aren't set up yet as
current user land expects this order to work.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
arch/x86/kvm/i8254.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 0150aff..ac06e2a 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -280,11 +280,15 @@ static struct kvm_timer_ops kpit_ops = {
.is_periodic = kpit_is_periodic,
};

-static void create_pit_timer(struct kvm_kpit_state *ps, u32 val, int is_period)
+static void create_pit_timer(struct kvm *kvm, u32 val, int is_period)
{
+ struct kvm_kpit_state *ps = &kvm->arch.vpit->pit_state;
struct kvm_timer *pt = &ps->pit_timer;
s64 interval;

+ if (!irqchip_in_kernel(kvm))
+ return;
+
interval = muldiv64(val, NSEC_PER_SEC, KVM_PIT_FREQ);

pr_debug("create pit timer, interval is %llu nsec\n", interval);
@@ -336,13 +340,13 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
/* FIXME: enhance mode 4 precision */
case 4:
if (!(ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)) {
- create_pit_timer(ps, val, 0);
+ create_pit_timer(kvm, val, 0);
}
break;
case 2:
case 3:
if (!(ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)){
- create_pit_timer(ps, val, 1);
+ create_pit_timer(kvm, val, 1);
}
break;
default:
--
1.7.12.1