linux-kernel - Re: [PATCH v2 36/43] powerpc/32: Set current->thread.regs in C interrupt entry

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Message-Id: <1615339900.vmbtzuirqw.astroid@bobo.none>
Date:   Wed, 10 Mar 2021 11:33:47 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 36/43] powerpc/32: Set current->thread.regs in C
 interrupt entry

Excerpts from Christophe Leroy's message of March 9, 2021 10:10 pm:
> No need to do that is assembly, do it in C.

Hmm. No issues with the patch as such, but why does ppc32 need this but 
not 64? AFAIKS 64 sets this when a thread is created.

Thanks,
Nick

> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/include/asm/interrupt.h | 4 +++-
>  arch/powerpc/kernel/entry_32.S       | 3 +--
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
> index 861e6eadc98c..e6d71c2e3aa2 100644
> --- a/arch/powerpc/include/asm/interrupt.h
> +++ b/arch/powerpc/include/asm/interrupt.h
> @@ -33,8 +33,10 @@ static inline void interrupt_enter_prepare(struct pt_regs *regs, struct interrup
>  	if (!arch_irq_disabled_regs(regs))
>  		trace_hardirqs_off();
>  
> -	if (user_mode(regs))
> +	if (user_mode(regs)) {
> +		current->thread.regs = regs;
>  		account_cpu_user_entry();
> +	}
>  #endif
>  	/*
>  	 * Book3E reconciles irq soft mask in asm
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 8fe1c3fdfa6e..815a4ff1ba76 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -52,8 +52,7 @@
>  prepare_transfer_to_handler:
>  	andi.	r0,r9,MSR_PR
>  	addi	r12, r2, THREAD
> -	beq	2f			/* if from user, fix up THREAD.regs */
> -	stw	r3,PT_REGS(r12)
> +	beq	2f
>  #ifdef CONFIG_PPC_BOOK3S_32
>  	kuep_lock r11, r12
>  #endif
> -- 
> 2.25.0
> 
>