Re: [Xen-devel] [PATCH v4 1/6] VMX: Statically assign two PI hooks

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.09.16 at 13:37, <JBeulich@xxxxxxxx> wrote:
>>>> On 21.09.16 at 04:37, <feng.wu@xxxxxxxxx> wrote:
>> PI hooks: vmx_pi_switch_from() and vmx_pi_switch_to() are
>> needed even when any previously assigned device is detached
>> from the domain. Since 'SN' bit is also used to control the
>> CPU side PI and we change the state of SN bit in these two
>> functions, then 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.
> 
> So if only SN left set is a problem, why do you need to also keep
> vmx_pi_switch_from in place? It's vmx_pi_switch_to() which clears
> the bit, and vmx_deliver_posted_intr() doesn't actively change it.

And it doesn't appear completely unreasonable for
vmx_pi_switch_to() to remove itself (when it gets run with
the "from" hook still NULL and no new device being in the
process of getting assigned).

Jan


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