Re: [PATCH v2 6/7] x86/power: Sprinkle some noinstr

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Jan 17, 2023 at 10:31:05AM +0100, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > +	/*
> > +	 * Definitely wrong, but at this point we should have at least enough
> > +	 * to do CALL/RET (consider SKL callthunks) and this avoids having
> > +	 * to deal with the noinstr explosion for now :/
> > +	 */
> > +	instrumentation_begin();
> 
> BTW., readability side note: instrumentation_begin()/end() are the 
> misnomers of the century - they don't signal the start/end of instrumented 
> code areas like the name falsely & naively suggests, but the exact 
> opposite: start/end of *non-*instrumented code areas.

Nope, they do as they say on the tin.

noinstr void foo(void)
{
}

declares the whole function as non-instrumented.

Within such functions, we demark regions where instrumentation is
allowed by:

noinstr void foo(void)
{
	instrumentation_begin();
	/* code that calls non-noinstr functions goes here */
	instrumentation_end();
}

(note the double negative in the comment)