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KVM: x86: Prevent starting PIT timers in the absence of irqchip support

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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>
This commit is contained in:
Jan Kiszka 2011-12-14 19:25:13 +01:00 committed by Avi Kivity
parent 4962516b23
commit 0924ab2cfa
1 changed files with 7 additions and 3 deletions
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10
arch/x86/kvm/i8254.c
View file

@ -338,11 +338,15 @@ static enum hrtimer_restart pit_timer_fn(struct hrtimer *data)
return HRTIMER_NORESTART;
}
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);
@ -394,13 +398,13 @@ 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: