linux-kernel - Re: [PATCH v2 28/43] powerpc/64e: Call bad_page_fault() from do_page

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Date:   Fri, 12 Mar 2021 09:39:56 +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 28/43] powerpc/64e: Call bad_page_fault() from
 do_page_fault()



Le 10/03/2021 à 02:29, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of March 9, 2021 10:09 pm:
>> book3e/64 is the last one calling __bad_page_fault()
>> from assembly.
>>
>> Save non volatile registers before calling do_page_fault()
>> and modify do_page_fault() to call __bad_page_fault()
>> for all platforms.
>>
>> Then it can be refactored by the call of bad_page_fault()
>> which avoids the duplication of the exception table search.
> 
> This can go in with the 64e change after your series. I think it should
> be ready for the next merge window as well.

Yes, I thought it would pull more optimisation, but at the end it doesn't bring anythink, so I'll 
drop it for now and leave it to you for your series.

> 
> Thanks,
> Nick
> 
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>   arch/powerpc/kernel/exceptions-64e.S |  8 +-------
>>   arch/powerpc/mm/fault.c              | 17 ++++-------------
>>   2 files changed, 5 insertions(+), 20 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
>> index e8eb9992a270..b60f89078a3f 100644
>> --- a/arch/powerpc/kernel/exceptions-64e.S
>> +++ b/arch/powerpc/kernel/exceptions-64e.S
>> @@ -1010,15 +1010,9 @@ storage_fault_common:
>>   	addi	r3,r1,STACK_FRAME_OVERHEAD
>>   	ld	r14,PACA_EXGEN+EX_R14(r13)
>>   	ld	r15,PACA_EXGEN+EX_R15(r13)
>> +	bl	save_nvgprs
>>   	bl	do_page_fault
>> -	cmpdi	r3,0
>> -	bne-	1f
>>   	b	ret_from_except_lite
>> -1:	bl	save_nvgprs
>> -	mr	r4,r3
>> -	addi	r3,r1,STACK_FRAME_OVERHEAD
>> -	bl	__bad_page_fault
>> -	b	ret_from_except
>>   
>>   /*
>>    * Alignment exception doesn't fit entirely in the 0x100 bytes so it
>> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
>> index 2e54bac99a22..7bcff3fca110 100644
>> --- a/arch/powerpc/mm/fault.c
>> +++ b/arch/powerpc/mm/fault.c
>> @@ -541,24 +541,15 @@ NOKPROBE_SYMBOL(___do_page_fault);
>>   
>>   static long __do_page_fault(struct pt_regs *regs)
>>   {
>> -	const struct exception_table_entry *entry;
>>   	long err;
>>   
>>   	err = ___do_page_fault(regs, regs->dar, regs->dsisr);
>>   	if (likely(!err))
>> -		return err;
>> -
>> -	entry = search_exception_tables(regs->nip);
>> -	if (likely(entry)) {
>> -		instruction_pointer_set(regs, extable_fixup(entry));
>>   		return 0;
>> -	} else if (!IS_ENABLED(CONFIG_PPC_BOOK3E_64)) {
>> -		__bad_page_fault(regs, err);
>> -		return 0;
>> -	} else {
>> -		/* 32 and 64e handle the bad page fault in asm */
>> -		return err;
>> -	}
>> +
>> +	bad_page_fault(regs, err);
>> +
>> +	return 0;
>>   }
>>   NOKPROBE_SYMBOL(__do_page_fault);
>>   
>> -- 
>> 2.25.0
>>
>>