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

Peter Zijlstra
2020-12-16T18:00:28Z

On Wed, Dec 16, 2020 at 10:56:05AM -0600, Josh Poimboeuf wrote:
> On Wed, Dec 16, 2020 at 09:40:59AM +0100, Peter Zijlstra wrote:

> > > 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?

What I meant was, they're either 2-3 wide and only a few instructions
long. Which greatly bounds the actual complexity of the algorithm,
however daft.

> > 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 ;-)

Please do, it could be getting all the niggly bits right exhausted my
brain enough to miss the obvious ;-)