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From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	npiggin@gmail.com
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v3 1/3] powerpc: Remove MSR_PR check in interrupt_exit_{user/kernel}_prepare()
Date: Wed, 25 Aug 2021 15:27:22 +1000	[thread overview]
Message-ID: <87zgt6aybp.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <385ead49ccb66a259b25fee3eebf0bd4094068f3.1629707037.git.christophe.leroy@csgroup.eu>

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.

cheers

  parent reply	other threads:[~2021-08-25  5:27 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-23  8:24 Christophe Leroy
2021-08-23  8:24 ` [PATCH v3 2/3] powerpc: Refactor verification of MSR_RI Christophe Leroy
2021-08-23  8:24 ` [PATCH v3 3/3] powerpc: Define and use MSR_RI only on non booke/40x Christophe Leroy
2021-08-25  4:54   ` Michael Ellerman
2021-08-25  6:21     ` Christophe Leroy
2021-08-25  5:27 ` Michael Ellerman [this message]
2021-08-25  5:45   ` [PATCH v3 1/3] powerpc: Remove MSR_PR check in interrupt_exit_{user/kernel}_prepare() Christophe Leroy
2021-08-25  6:56     ` Michael Ellerman
2021-08-27 13:16 ` (subset) " Michael Ellerman
2021-08-31 14:00 ` Michael Ellerman

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