On Mon, Jun 10, 2013 at 02:42:29PM +0200, Ralf Baechle wrote:
> On Mon, Jun 10, 2013 at 01:00:01PM +0530, Jayachandran C wrote:
>
> > Kernel threads should be able to use COP2 if the platform needs it.
> > Do not call die_if_kernel() for a coprocessor unusable exception if
> > the exception due to COP2 usage. Instead, the default notifier for
> > COP2 exceptions is updated to call die_if_kernel.
> >
> > Signed-off-by: Jayachandran C <jchandra@xxxxxxxxxxxx>
> > ---
> > arch/mips/kernel/traps.c | 15 +++++----------
> > 1 file changed, 5 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
> > index beba1e6..142d2be 100644
> > --- a/arch/mips/kernel/traps.c
> > +++ b/arch/mips/kernel/traps.c
> > @@ -1056,15 +1056,9 @@ static int default_cu2_call(struct notifier_block *nfb, unsigned long action,
> > {
> > struct pt_regs *regs = data;
> >
> > - switch (action) {
> > - default:
> > - die_if_kernel("Unhandled kernel unaligned access or invalid "
> > + die_if_kernel("COP2: Unhandled kernel unaligned access or invalid "
> > "instruction", regs);
> > - /* Fall through */
> > -
> > - case CU2_EXCEPTION:
> > - force_sig(SIGILL, current);
> > - }
> > + force_sig(SIGILL, current);
> >
> > return NOTIFY_OK;
> > }
>
> The idea for cu2_chain notifiers is that they should return a value with
> NOTIFY_STOP_MASK set. That would prevent further calls to other notifiers.
> The default_cu2_call() notifier is installed with the lowest possible
> priority and is meant to only be called if there is no other notifier was
> installed, that is on a bog standard MIPS core with no CP2.
I am trying to move the die_if_kernel from do_cpu() to here for COP2
exceptions. In the existing code, COP2 unusable exception calls
die_if_kernel in do_cpu() itself, so COP2 unusable generated by kernel
threads will not make it to the notifiers. With this change (and the
one below), die_if_kernel() is called only if the all the notifiers
pass it thru.
>
> > @@ -1080,10 +1074,11 @@ asmlinkage void do_cpu(struct pt_regs *regs)
> > unsigned long __maybe_unused flags;
> >
> > prev_state = exception_enter();
> > - die_if_kernel("do_cpu invoked from kernel context!", regs);
> > -
> > cpid = (regs->cp0_cause >> CAUSEB_CE) & 3;
> >
> > + if (cpid != 2)
> > + die_if_kernel("do_cpu invoked from kernel context!", regs);
> > +
> > switch (cpid) {
> > case 0:
> > epc = (unsigned int __user *)exception_epc(regs);
>
> I'm ok with this segment.
>
> Ralf
JC.
