Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch

[Peter Zijlstra]

On Tue, Feb 19, 2019 at 10:15:25AM +0100, Peter Zijlstra wrote:
> On Mon, Feb 18, 2019 at 04:24:30PM -0800, Linus Torvalds wrote:
> > On Mon, Feb 18, 2019 at 2:31 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> > >
> > > The question is what "fix it" means. I'm really concerned about AC escapes,
> > > and everyone else should be, too.
> > 
> > I do think that it might be the right thing to do to add some kind of
> > WARN_ON_ONCE() for AC being set in various can-reschedule situations.
> 
> So I disagree.
> 
> Either we set AC with preempt disabled, and then we don't need an extra
> warning, because we already have a warning about scheduling with
> preemption disabled, or we accept that the fault handler can run.

n/m about the faults, forgot the obvious :/

I still really dislike wrecking the preemption model over this.