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SubjectRe: [PATCH v3 1/3] powerpc: Remove MSR_PR check in interrupt_exit_{user/kernel}_prepare()
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Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> Le 25/08/2021 à 07:27, Michael Ellerman a écrit :
>> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
>>> In those hot functions that are called at every interrupt, any saved
>>> cycle is worth it.
>>>
>>> interrupt_exit_user_prepare() and interrupt_exit_kernel_prepare() are
>>> called from three places:
>>> - From entry_32.S
>>> - From interrupt_64.S
>>> - From interrupt_exit_user_restart() and interrupt_exit_kernel_restart()
>>>
>>> In entry_32.S, there are inambiguously called based on MSR_PR:
>>>
>>> interrupt_return:
>>> lwz r4,_MSR(r1)
>>> addi r3,r1,STACK_FRAME_OVERHEAD
>>> andi. r0,r4,MSR_PR
>>> beq .Lkernel_interrupt_return
>>> bl interrupt_exit_user_prepare
>>> ...
>>> .Lkernel_interrupt_return:
>>> bl interrupt_exit_kernel_prepare
>>>
>>> In interrupt_64.S, that's similar:
>>>
>>> interrupt_return_\srr\():
>>> ld r4,_MSR(r1)
>>> andi. r0,r4,MSR_PR
>>> beq interrupt_return_\srr\()_kernel
>>> interrupt_return_\srr\()_user: /* make backtraces match the _kernel variant */
>>> addi r3,r1,STACK_FRAME_OVERHEAD
>>> bl interrupt_exit_user_prepare
>>> ...
>>> interrupt_return_\srr\()_kernel:
>>> addi r3,r1,STACK_FRAME_OVERHEAD
>>> bl interrupt_exit_kernel_prepare
>>>
>>> In interrupt_exit_user_restart() and interrupt_exit_kernel_restart(),
>>> MSR_PR is verified respectively by BUG_ON(!user_mode(regs)) and
>>> BUG_ON(user_mode(regs)) prior to calling interrupt_exit_user_prepare()
>>> and interrupt_exit_kernel_prepare().
>>>
>>> The verification in interrupt_exit_user_prepare() and
>>> interrupt_exit_kernel_prepare() are therefore useless and can be removed.
>>>
>>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>>> Acked-by: Nicholas Piggin <npiggin@gmail.com>
>>> ---
>>> arch/powerpc/kernel/interrupt.c | 2 --
>>> 1 file changed, 2 deletions(-)
>>
>> I'll pick this one up independent of the other two patches.
>
> Second patch should be ok as well, no ?

Yeah I guess.

I'm not sure if we'll want to keep cpu_has_msr_ri() if we have a
CONFIG_PPC_MSR_RI, but that's a pretty minor detail.

So yeah I'll take patch 2 as well.

cheers

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