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

Peter Zijlstra
2019-02-19T11:58:55Z

On Tue, Feb 19, 2019 at 12:38:42PM +0100, Thomas Gleixner wrote:
> On Tue, 19 Feb 2019, Peter Zijlstra wrote:
>
> > On Tue, Feb 19, 2019 at 10:04:09AM +0100, Peter Zijlstra wrote:
> > > > Does that make more sense?
> > >
> > > It appears to me you're going about it backwards.
> >
> > So how about you do a GCC plugin that verifies limits on code-gen
> > between user_access_begin/user_access_end() ?
> >
> > - No CALL/RET
> > - implies user_access_end() happens
> > - implies no fentry hooks
> > - No __preempt_count frobbing
> > - No tracepoints
> > - ...
> >
> > That way you put the burden on the special code, not on the rest of the
> > kernel.
>
> And then you have kprobes ....

They prod the INT3 byte and then take an exception, and exceptions are
'fine'.