Re: [Xen-devel] [PATCH v3 1/6] VMX: Statically assign two PI hooks

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Dario Faggioli [mailto:dario.faggioli@xxxxxxxxxx]
> Sent: Tuesday, September 6, 2016 4:43 PM
> To: Wu, Feng <feng.wu@xxxxxxxxx>; xen-devel@xxxxxxxxxxxxx
> Cc: Tian, Kevin <kevin.tian@xxxxxxxxx>; george.dunlap@xxxxxxxxxxxxx;
> andrew.cooper3@xxxxxxxxxx; jbeulich@xxxxxxxx
> Subject: Re: [Xen-devel] [PATCH v3 1/6] VMX: Statically assign two PI hooks
> 
> On Wed, 2016-08-31 at 11:56 +0800, Feng Wu wrote:
> > PI hooks: vmx_pi_switch_from() and vmx_pi_switch_to() are
> > needed even all the assigned devices were dettached from
> > the domain.
> >
> maybe "are needed even when any previously passed through device is
> detached from the domain" (or something like that)?

Looks good, thanks for improve the wording.

> 
> > We change the state of SN bit in these two
> > functions, and evaluate this bit in vmx_deliver_posted_intr()
> > when trying to deliver the interrupt in posted way via software.
> > The problem is if we deassign the hooks while the vCPU is runnable
> > in the runqueue with 'SN' set, all the furture notificaton event
> > will be suppressed. This patch makes these two hooks statically
> > assigned.
> >
> Which, if SN is used only for controlling VT-d PI from passed thru
> devices does not sound like an issue to me.
> 
> What I sort of get from the discussion you had with Jan, however, is
> that this is an issue, because SN is also used for other things, i.e.,
> it is indeed useful even when there are no passed thru device, is that
> the case?
> 
> If yes, I think this deserves at least a quick mention in the sentence
> above.

Yes, SN controls all the PI including CPU side PI activity, sure, I will
explicitly add those information.

Thanks,
Feng

> 
> 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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