From: Matt Lupfer <mlup...@ddn.com>
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 <mlup...@ddn.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Reviewed-by: Paolo Bonzini <pbonz...@redhat.com>
---
hw/timer/hpet.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c
index 1264dfd..e15d6bc 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);
--
MST
