From c36ad13fe9ece9a21a8c1dd082473a2b182298ee Mon Sep 17 00:00:00 2001 From: Matt Lupfer Date: Fri, 21 Feb 2014 21:37:23 -0700 Subject: Don't enable a HPET timer if HPET is disabled A HPET timer can be started when HPET is not yet enabled. This will not generate an interrupt to the guest, but causes problems when HPET is later enabled. A timer that is created and expires at least once before HPET is enabled will have an initialized comparator based on a hpet_offset of 0 (uninitialized). When HPET is enabled, hpet_set_timer() is called a second time, which modifies the timer expiry to a time based on the difference between current ticks (measured with the newly initialized hpet_offset) and the timer's comparator (which was generated before hpet_offset was initialized). This results in a long period of no HPET timer ticks. When this occurs with a CentOS 5.x guest, the guest may not receive timer interrupts during its narrow timer check window and panic on boot. Signed-off-by: Matt Lupfer Acked-by: Michael S. Tsirkin Reviewed-by: Paolo Bonzini --- hw/timer/hpet.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'hw') diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c index 1264dfd46a..e15d6bcac7 100644 --- a/hw/timer/hpet.c +++ b/hw/timer/hpet.c @@ -506,7 +506,8 @@ static void hpet_ram_write(void *opaque, hwaddr addr, timer->cmp = (uint32_t)timer->cmp; timer->period = (uint32_t)timer->period; } - if (activating_bit(old_val, new_val, HPET_TN_ENABLE)) { + if (activating_bit(old_val, new_val, HPET_TN_ENABLE) && + hpet_enabled(s)) { hpet_set_timer(timer); } else if (deactivating_bit(old_val, new_val, HPET_TN_ENABLE)) { hpet_del_timer(timer); -- cgit v1.2.1