Re: [PATCH 01/26] mm: asi: Make some utility functions noinstr compatible

[Junaid Shahid <junaids@google.com>]

On 10/25/24 6:21 AM, Brendan Jackman wrote:
> Hey Boris,
> 
> On Fri, 25 Oct 2024 at 13:41, Borislav Petkov <bp@alien8.de> wrote:
>>
>> On Fri, Jul 12, 2024 at 05:00:19PM +0000, Brendan Jackman wrote:
>>> +/*
>>> + * Can be used for functions which themselves are not strictly noinstr, but
>>> + * may be called from noinstr code.
>>> + */
>>> +#define inline_or_noinstr                                            \
>>
>> Hmm, this is confusing. So is it noinstr or is it getting inlined?
> 
> We don't care if it's getting inlined, which is kinda the point. This
> annotation means "you may call this function from noinstr code". My
> current understanding is that the normal noinstr annotation means
> "this function fundamentally mustn't be instrumented".
> 
> So with inline_or_noinstr you get:
> 
> 1. "Documentation" that the function itself doesn't have any problem
> with getting traced etc.
> 2. Freedom for the compiler to inline or not.
> 
>> I'd expect you either always inline the small functions - as you do for some
>> aleady - or mark the others noinstr. But not something in between.
>>
>> Why this?
> 
> Overall it's pretty likely I'm wrong about the subtlety of noinstr's
> meaning. And the benefits I listed above are pretty minor. I should
> have looked into this as it would have been an opportunity to reduce
> the patch count of this RFC!
> 
> Maybe I'm also forgetting something more important, perhaps Junaid
> will weigh in...

Yes, IIRC the idea was that there is no need to prohibit inlining for this class 
of functions.