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

Nicholas Piggin
2021-02-09T02:03:20Z

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.

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
>
>