Re: [PATCH v3 03/11] x86/vlapic: introduce an EOI callback mechanism

[Jan Beulich <jbeulich@suse.com>]

On 08.04.2021 11:12, Roger Pau Monné wrote:
> On Thu, Apr 08, 2021 at 08:20:15AM +0200, Jan Beulich wrote:
>> On 07.04.2021 18:27, Roger Pau Monné wrote:
>>> On Wed, Apr 07, 2021 at 04:55:43PM +0200, Jan Beulich wrote:
>>>> On 31.03.2021 12:32, Roger Pau Monne wrote:
>>>>> Add a new vlapic_set_irq_callback helper in order to inject a vector
>>>>> and set a callback to be executed when the guest performs the end of
>>>>> interrupt acknowledgment.
>>>>>
>>>>> Such functionality will be used to migrate the current ad hoc handling
>>>>> done in vlapic_handle_EOI for the vectors that require some logic to
>>>>> be executed when the end of interrupt is performed.
>>>>>
>>>>> The setter of the callback will be in charge for setting the callback
>>>>> again on resume. That is the reason why vlapic_set_callback is not a
>>>>> static function.
>>>>
>>>> I'm struggling with your use of "resume" here: Resuming from S3
>>>> doesn't require re-doing anything that's kept in memory, does it?
>>>> So what meaning does the word have here?
>>>
>>> Right, I can see the confusion. Resume here means a guest being
>>> migrated or restored, not Xen itself being resumed. Callbacks are not
>>> part of the exported guest state, and hence any emulated device that
>>> requires a callback will have to register it as part of loading the
>>> saved state.
>>>
>>>> Apart from this, and with the xzalloc_array() change requested
>>>> by Andrew, this looks good to me.
>>
>> In which case with this change and "resume" replaced suitably in the
>> description
> 
> I've worded it as:
> 
> "The setter of the callback will be in charge for setting the callback
> again on guest restore or resume, as callbacks are not saved as part
> of the vlapic state. That is the reason why vlapic_set_callback is not
> a static function."

Hmm, you still mention "resume", which makes me continue to wonder
what you're thinking of beyond guest restore.

Jan