Re: [PATCH v4 2/4] xen/arm: Handle cases when hardware_domain is NULL

[Luca Fancellu <luca.fancellu@xxxxxxx>]

> On 14 Apr 2021, at 14:45, Julien Grall <julien@xxxxxxx> wrote:
> 
> Hi Luca,
> 
> On 14/04/2021 12:29, Luca Fancellu wrote:
>>> On 14 Apr 2021, at 12:16, Julien Grall <julien@xxxxxxx> wrote:
>>> 
>>> Hi Luca,
>>> 
>>> On 14/04/2021 10:14, Luca Fancellu wrote:
>>>> Among the common and arm codebase there are few cases where
>>>> the hardware_domain variable is checked to see if the current
>>>> domain is equal to the hardware_domain, change this cases to
>>>> use is_hardware_domain() function instead. >
>>>> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
>>>> ---
>>>> v4 changes:
>>>> - removed unneeded check for domain NULL from is_hardware_domain
>>>>   introduced in v3
>>> 
>>> After this change, this patch is only avoid to open-code 
>>> is_hardware_domain(). Although, it adds an extra speculation barrier.
>>> 
>>> I am not against the change, however I think the commit message needs to 
>>> updated to match what the patch is doing.
>>> 
>>> Can you propose a new commit message?
>> Hi Julien,
>> Yes I agree, what about:
>> xen/arm: Reinforce use of is_hardware_domain
>> Among the common and arm codebase there are few cases where
> 
> I would drop 'common' because you are only modifying the arm codebase.
> 
>> the hardware_domain variable is checked to see if the current
>> domain is equal to the hardware_domain, change this cases to
>> use is_hardware_domain() function instead.
> 
> 
>> In the eventuality that hardware_domain is NULL, is_hardware_domain
>> will return false because an analysis of the common and arm codebase
>> shows that is_hardware_domain is called always with a non NULL
>> domain pointer.
> 
> This paragraph seems to come out of the blue. I would drop it.
> 
> How about:
> 
> "
> There are a few places on Arm where we use pretty much an open-coded version 
> of is_hardware_domain(). The main difference, is the helper will also block 
> speculation (not yet implemented on Arm).
> 
> The existing users are not in hot path, so blocking speculation would not 
> hurt when it is implemented. So remove the open-coded version within the arm 
> codebase.
> "
> 
> If you are happy with the commit message, I will commit it the series 
> tomorrow (to give an opportunity to Stefano to review).
> 

Hi Julien,

Yes your version is much better, thank you very much!

Cheers,
Luca

> Cheers,
> 
> -- 
> Julien Grall