Re: [PATCH v5 18/22] powerpc/syscall: Remove FULL_REGS verification in system_call_exception

Christophe Leroy
2021-02-09T14:32:34Z

Le 09/02/2021 à 03:02, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of February 9, 2021 1:10 am:
>> For book3s/64, FULL_REGS() is 'true' at all time, so the test voids.
>> For others, non volatile registers are saved inconditionally.
>>
>> So the verification is pointless.
>>
>> Should one fail to do it, it would anyway be caught by the
>> CHECK_FULL_REGS() in copy_thread() as we have removed the
>> special versions ppc_fork() and friends.
>>
>> null_syscall benchmark reduction 4 cycles (332 => 328 cycles)
>
> I wonder if we rather make a CONFIG option for a bunch of these simpler
> debug checks here (and also in interrupt exit, wrappers, etc) rather
> than remove them entirely.

We can drop this patch if you prefer. Anyway, like book3s/64, once ppc32 also do interrupt
entry/exit in C, FULL_REGS() will already return true.

Christophe

>
> Thanks,
> Nick
>
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> ---
>> arch/powerpc/kernel/interrupt.c | 1 -
>> 1 file changed, 1 deletion(-)
>>
>> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
>> index 8fafca727b8b..55e1aa18cdb9 100644
>> --- a/arch/powerpc/kernel/interrupt.c
>> +++ b/arch/powerpc/kernel/interrupt.c
>> @@ -42,7 +42,6 @@ notrace long system_call_exception(long r3, long r4, long r5,
>> if (!IS_ENABLED(CONFIG_BOOKE) && !IS_ENABLED(CONFIG_40x))
>> BUG_ON(!(regs->msr & MSR_RI));
>> BUG_ON(!(regs->msr & MSR_PR));
>> - BUG_ON(!FULL_REGS(regs));
>> BUG_ON(arch_irq_disabled_regs(regs));
>>
>> #ifdef CONFIG_PPC_PKEY
>> --
>> 2.25.0
>>
>>