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Message-ID: <87zgt6aybp.fsf@mpe.ellerman.id.au>
Date: Wed, 25 Aug 2021 15:27:22 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Christophe Leroy <christophe.leroy@...roup.eu>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>, npiggin@...il.com
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 1/3] powerpc: Remove MSR_PR check in
interrupt_exit_{user/kernel}_prepare()
Christophe Leroy <christophe.leroy@...roup.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@...roup.eu>
> Acked-by: Nicholas Piggin <npiggin@...il.com>
> ---
> arch/powerpc/kernel/interrupt.c | 2 --
> 1 file changed, 2 deletions(-)
I'll pick this one up independent of the other two patches.
cheers
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