Re: irq_guest_eoi_timer interaction with MSI

[Keir Fraser <keir.fraser@eu.citrix.com>]

On 25/11/08 10:12, "Jan Beulich" <jbeulich@novell.com> wrote:

>>>> Keir Fraser <keir.fraser@eu.citrix.com> 24.11.08 18:02 >>>
>> Setting the need-a-hypercall bit looks racey. Don't you need to set the bit,
>> then check the guest didn't unmask meanwhile?
> 
> What would the action be in that case? Try send_guest_pirq() a second
> time, and not arm the timer (along with clearing all the bits again) if one
> of the guests is now able to accept it? Would seem too complicated to me
> (the more that then the HVM case would need to be taken care of
> explicitly), given that all we try to avoid is a 1ms gap in delivering the
> next event. But it would be doable of course.

Yes, I think it would be something like that. As you say, the patch you
propose is a strict improvement on the current state of affairs, so we can
just go with that and extend it only if it proves necessary.

 -- Keir