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

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

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)?

> 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.

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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