KVM: x86: Prevent starting PIT timers in the absence of irqchip support
authorJan Kiszka <jan.kiszka@siemens.com>
Wed, 14 Dec 2011 18:25:13 +0000 (19:25 +0100)
committerAvi Kivity <avi@redhat.com>
Sun, 25 Dec 2011 15:13:18 +0000 (17:13 +0200)
commit0924ab2cfa98b1ece26c033d696651fd62896c69
tree87b23ddd025d5c44ebaa941b92c8cd8ade6af703
parent4962516b2309d76964f9df0d33e74f43b624a42d
KVM: x86: Prevent starting PIT timers in the absence of irqchip support

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>
arch/x86/kvm/i8254.c