On Tue, Jun 20, 2017 at 12:16:40PM +0530, Anshuman Khandual wrote: > On 06/19/2017 11:29 PM, Ram Pai wrote: > > On Mon, Jun 19, 2017 at 09:06:13PM +1000, Michael Ellerman wrote: > >> Ram Pai <linux...@us.ibm.com> writes: > >> > >>> Signed-off-by: Ram Pai <linux...@us.ibm.com> > >>> --- > >>> arch/powerpc/kernel/exceptions-64s.S | 16 ++++++++++------ > >>> 1 file changed, 10 insertions(+), 6 deletions(-) > >>> > >>> diff --git a/arch/powerpc/kernel/exceptions-64s.S > >>> b/arch/powerpc/kernel/exceptions-64s.S > >>> index 8db9ef8..a4de1b4 100644 > >>> --- a/arch/powerpc/kernel/exceptions-64s.S > >>> +++ b/arch/powerpc/kernel/exceptions-64s.S > >>> @@ -493,13 +493,15 @@ EXC_COMMON_BEGIN(data_access_common) > >>> ld r12,_MSR(r1) > >>> ld r3,PACA_EXGEN+EX_DAR(r13) > >>> lwz r4,PACA_EXGEN+EX_DSISR(r13) > >>> + std r3,_DAR(r1) > >>> + std r4,_DSISR(r1) > >>> #ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS > >>> + andis. r0,r4,DSISR_KEYFAULT@h /* save AMR only if its a key fault */ > >>> + beq+ 1f > >> > >> This seems to be incremental on top of one of your other patches. > >> > >> But I don't see why, can you please just squash this into whatever patch > >> adds this code in the first place. > > > > It was an optimization added later. But yes it can be squashed into an > > earlier patch. > > Could you please explain what is the optimization this achieves ?
Don't want to read the AMR if it is not a key protection fault. This is a hot-hot-path. A few cycles saved can accumulate into signficant savings overall. RP
