On Fri, Jun 22, 2018 at 01:59:44PM +0200, Thomas Gleixner wrote:
> On Fri, 22 Jun 2018, Thomas Gleixner wrote:
> > The whole thing is simply:
> >
> > handle_ac()
> > {
> > if (user_mode(regs)) {
> > do_trap(AC, SIGBUS, ...);
> > } else {
> > disable_ac_on_local_cpu();
> > WARN_ONCE(1);
> > }
> > }
> >
> > That wants #AC enabled as early as possible so the kernel gets as much
> > coverage as it can. If it trips in the kernel it's a bug and needs to be
> > fixed and we can them fix ONE by ONE.
>
> That said, #AC is just yet another badly defined and hastily bolted on
> (mis)feature. This should have been:
>
> Bit A: Enable #AC if CPL < 3
> Bit B: Enable #AC if CPL == 3
>
> But that would have been too useful and would allow sensible use of #AC
> without creating software trainwrecks.
>
The two bits would be ideal.
So I will do SIGBUG for user and WARN/disable for kernel in the next version.
Thanks.
-Fenghua
