Re: [Qemu-devel] [PATCH] rtc: placing RTC memory region outside BQL

[Paolo Bonzini]

On 04/02/2018 19:02, Peter Maydell wrote:
> On 1 February 2018 at 14:23, Paolo Bonzini <address@hidden> wrote:
>> On 01/02/2018 08:47, Gonglei wrote:
>>> diff --git a/hw/timer/mc146818rtc.c b/hw/timer/mc146818rtc.c
>>> index 35a05a6..d9d99c5 100644
>>> --- a/hw/timer/mc146818rtc.c
>>> +++ b/hw/timer/mc146818rtc.c
>>> @@ -986,6 +986,7 @@ static void rtc_realizefn(DeviceState *dev, Error 
>>> **errp)
>>>      qemu_register_suspend_notifier(&s->suspend_notifier);
>>>
>>>      memory_region_init_io(&s->io, OBJECT(s), &cmos_ops, s, "rtc", 2);
>>> +    memory_region_clear_global_locking(&s->io);
>>>      isa_register_ioport(isadev, &s->io, base);
>>>
>>>      qdev_set_legacy_instance_id(dev, base, 3);
>>>
>>
>> This is not enough, you need to add a new lock or something like that.
>> Otherwise two vCPUs can access the RTC together and make a mess.
> 
> Do you also need to do something to take the global lock before
> raising the outbound IRQ line (since it might be connected to a device
> that does need the global lock), or am I confused ?

Yes, that's a good point.  Most of the time the IRQ line is raised in a
timer, but not always.

Paolo