Re: [PATCH RFC v1] arm64: Handle traps from accessing CNTVCT/CNTFRQ for CONFIG_COMPAT

[Nicolin Chen <nicoleotsuka@gmail.com>]

Hello Marc,

On Thu, Jan 11, 2018 at 08:51:37AM +0000, Marc Zyngier wrote:
> > [ I also added cntfrq here for safety as theoretically it could
> >   trigger the trap as well. However, my another test case (with
> >   mrc insturction) doesn't seem to trigger a trap. So I would
> >   drop it in the next version if someone can confirm it's not
> >   required. Thanks -- Nicolin ]
> 
> See my previous series on this very subject[1] as well as Will's reply.

Thanks for the background.

> > -	for (hook = sys64_hooks; hook->handler; hook++)
> > +	for (; hook && hook->handler; hook++)
> >  		if ((hook->esr_mask & esr) == hook->esr_val) {
> >  			hook->handler(esr, regs);
> >  			return;
> > 
> 
> Also, this code is fairly broken in its handling of conditional
> instructions.

I understand that it should take care of the condition field as
a general instruction handler. Just for curiosity: If we confine
the topic to read access of CNTVCT/CNTFRQ, what'd be the penalty
by ignoring the condition field and executing it anyway?

Thank you
Nicolin