Re: [PATCH v2 00/12] x86: major paravirt cleanup

Josh Poimboeuf
2020-12-16T16:58:10Z

On Wed, Dec 16, 2020 at 09:40:59AM +0100, Peter Zijlstra wrote:
> > So much algorithm.
>
> :-)
>
> It's not really hard, but it has a few pesky details (as always).

It really hurt my brain to look at it.

> > Could we make it easier by caching the shared
> > per-alt-group CFI state somewhere along the way?
>
> Yes, but when I tried it grew the code required. Runtime costs would be
> less, but I figured that since alternatives are typically few and small,
> that wasn't a real consideration.

Aren't alternatives going to be everywhere now with paravirt using them?

> That is, it would basically cache the results of find_alt_unwind(), but
> you still need find_alt_unwind() to generate that data, and so you gain
> the code for filling and using the extra data structure.
>
> Yes, computing it 3 times is naf, but meh.

Haha, I loved this sentence.

> > Thoughts? This is all theoretical of course, I could try to do a patch
> > tomorrow.
>
> No real objection, I just didn't do it because 1) it works, and 2) even
> moar lines.

I'm kind of surprised it would need moar lines. Let me play around with
it and maybe I'll come around ;-)

--
Josh