Re: [Xen-devel] [PATCH v7 15/17] vmx: VT-d posted-interrupt core logic handling

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Mon, 2015-09-21 at 12:22 +0000, Wu, Feng wrote:
> 
> > -----Original Message-----
> > From: George Dunlap [mailto:george.dunlap@xxxxxxxxxx]

> > You also need to check that local_events_need_delivery() will
> > return
> > "true" if you get an interrupt between that time and entering the
> > hypervisor.  Will that happen automatically from
> > hvm_local_events_need_delivery() -> hvm_vcpu_has_pending_irq() ->
> > vlapic_has_pending_irq()?  Or will you need to add a hook in
> > hvm_vcpu_has_pending_irq()?
> 
> I think I don't need to add hook in hvm_vcpu_has_pending_irq(), what
> I need
> to do in vcpu_block() and do_poll() is as below:
> 
> 1. set_bit(_VPF_blocked, &v->pause_flags);
> 
> 2. ret = v->arch.arch_block(), in this hook, we can re-use the same
> logic in
> vmx_pre_ctx_switch_pi(), and check whether ON bit is set during
> updating
> posted-interrupt descriptor, can return 1 when ON is set
>
It think it would be ok for an hook to return a value (maybe, if doing
that, let's pick variable names and use comments to explain what goes
on as good as we can).

I think I also see why you seem to prefer doing it that way, rather
than hacking local_events_need_delivery(), but can you please elaborate
on that? (My feeling is that you want to avoid having to update the
data structures in between _VPF_blocked and the check
local_events_need_delivery(), and then having to roll such update back
if local_events_need_delivery() ends up being false, is that the
case?).

Code would look better, IMO, if we manage to fold that somehow inside
local_events_need_delivery(), but that:
 1. is hard to tell without actually seeing how the code will end up 
    being
 2. might be my opinion only, so let's see what others think.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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