linux-kernel - Re: [PATCH] powerpc/interrupt: Don't read MSR from interrupt_exit_kernel

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Message-Id: <168836201884.50010.18257455967677978392.b4-ty@ellerman.id.au>
Date:   Mon, 03 Jul 2023 15:26:58 +1000
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/interrupt: Don't read MSR from interrupt_exit_kernel_prepare()

On Mon, 05 Jun 2023 10:55:26 +0200, Christophe Leroy wrote:
> A disassembly of interrupt_exit_kernel_prepare() shows a useless read
> of MSR register. This is shown by r9 being re-used immediately without
> doing anything with the value read.
> 
>   c000e0e0:       60 00 00 00     nop
>   c000e0e4:       7d 3a c2 a6     mfmd_ap r9
>   c000e0e8:       7d 20 00 a6     mfmsr   r9
>   c000e0ec:       7c 51 13 a6     mtspr   81,r2
>   c000e0f0:       81 3f 00 84     lwz     r9,132(r31)
>   c000e0f4:       71 29 80 00     andi.   r9,r9,32768
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/interrupt: Don't read MSR from interrupt_exit_kernel_prepare()
      https://git.kernel.org/powerpc/c/0eb089a72fda3f7969e6277804bde75dc1474a14

cheers