Re: [Qemu-devel] [PATCH] Don't enable a HPET timer if HPET is disabled

[Matt Lupfer]

On 02/22/2014 02:01 AM, Paolo Bonzini wrote:
> Il 22/02/2014 05:37, Matt Lupfer ha scritto:
>> 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 <address@hidden>
>> ---
>>  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);
>>
> 
> Reviewed-by: Paolo Bonzini <address@hidden>

Ping?  Now that 1.7.1 is out, I hope this small patch will be considered
for the 2.0 release.

http://patchwork.ozlabs.org/patch/323121/

Matt