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

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Date:   Thu, 11 Mar 2021 11:38:58 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Piggin <npiggin@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        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



Le 10/03/2021 à 02:33, Nicholas Piggin a écrit :
> 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.

Looks like ppc64 was doing the same in function save_remaining_regs() in arch/ppc64/kernel/head.S 
until commit https://github.com/mpe/linux-fullhistory/commit/e5bb080d

But I can't find what happend to it in that commit.

Where is it done now ? Maybe that's also already done for ppc32.

Thanks
Christophe


> 
> 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
>>
>>