On Thu, 2021-09-16 at 17:15 +1000, Benjamin Herrenschmidt wrote: > On Wed, 2021-09-15 at 16:31 +0200, Christophe Leroy wrote: > > dcbz instruction shouldn't be used on non-cached memory. Using > > it on non-cached memory can result in alignment exception and > > implies a heavy handling. > > > > Instead of silentely emulating the instruction and resulting in > > high > > performance degradation, warn whenever an alignment exception is > > taken due to dcbz, so that the user is made aware that dcbz > > instruction has been used unexpectedly. > > > > Reported-by: Stan Johnson <user...@yahoo.com> > > Cc: Finn Thain <fth...@linux-m68k.org> > > Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu> > > --- > > arch/powerpc/kernel/align.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/powerpc/kernel/align.c > > b/arch/powerpc/kernel/align.c > > index bbb4181621dd..adc3a4a9c6e4 100644 > > --- a/arch/powerpc/kernel/align.c > > +++ b/arch/powerpc/kernel/align.c > > @@ -349,6 +349,7 @@ int fix_alignment(struct pt_regs *regs) > > if (op.type != CACHEOP + DCBZ) > > return -EINVAL; > > PPC_WARN_ALIGNMENT(dcbz, regs); > > + WARN_ON_ONCE(1); > > This is heavy handed ... It will be treated as an oops by various > things uselessly spit out a kernel backtrace. Isn't > PPC_WARN_ALIGNMENT > enough ?
Ah I saw your other one about fbdev... Ok what about you do that in a if (!user_mode(regs)) ? Indeed the kernel should not do that. Cheers, Ben.