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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 <mlupfer@ddn.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
master
Matt Lupfer 2014-02-21 21:37:23 -07:00 committed by Michael S. Tsirkin
parent 5c31207941
commit c36ad13fe9
1 changed files with 2 additions and 1 deletions
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3
hw/timer/hpet.c
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@ -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);