Re: [Qemu-devel] [PATCH] pc: Clean up PIC-to-APIC IRQ path

[Blue Swirl]

On Mon, Aug 29, 2011 at 9:13 PM, Avi Kivity <address@hidden> wrote:
> On 08/30/2011 12:06 AM, Jan Kiszka wrote:
>>
>> >
>> >  Does this need to be save/restored for migration?
>>
>> Nope, but we need some other measure. I thought to remember the pic was
>> refreshing this after load, but I do not find any traces of this now. We
>> likely need a post_load handler in the i8259 that re-asserts the IRQ as
>> required.
>>
>
> We need some kind of two phase restore. In the first phase all state is
> restored; since some of that state drivers outputs that are input to other
> devices, they may experience an edge, and we need to supress that.  In the
> second phase edge detection is unsupressed and the device goes live.

No. Devices may not perform any externally visible activities (like
toggle a qemu_irq) during or after load because 1) qemu_irq is
stateless and 2) since the receiving end is also freshly loaded, both
states are already in synch without any calls or toggling.