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Gmane
From: Jan Kiszka <jan.kiszka <at> siemens.com>
Subject: [PATCH 1/2] KVM: x86: Prevent starting PIT timers in the absence of irqchip support
Newsgroups: gmane.comp.emulators.kvm.devel
Date: Wednesday 14th December 2011 18:25:13 UTC (over 5 years ago)
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: [] kvm_set_irq+0x30/0x170 [kvm]
...
Call Trace:
 [] pit_do_work+0x51/0xd0 [kvm]
 [] process_one_work+0x111/0x4d0
 [] worker_thread+0x152/0x340
 [] kthread+0x7e/0x90
 [] 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 <[email protected]>
---

This is for stable, the next patch just a cleanup.

 arch/x86/kvm/i8254.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 76e3f1c..405f262 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -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:
-- 
1.7.3.4
--
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CD: 3ms