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

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>

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 0150affad25d082c4dd8eea9546b30ee12491731..ac06e2a423b84831b17a7855a1827dfb26f4ec85 100644 (file)
--- 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: