linux-kernel - Re: [PATCH v4 20/23] powerpc/syscall: Do not check unsupported scv vector on PPC32

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Date:   Mon, 8 Feb 2021 18:45:43 +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>, msuchanek@...e.de,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v4 20/23] powerpc/syscall: Do not check unsupported scv
 vector on PPC32



Le 26/01/2021 à 11:16, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of January 26, 2021 12:48 am:
>> Only PPC64 has scv. No need to check the 0x7ff0 trap on PPC32.
>>
>> And ignore the scv parameter in syscall_exit_prepare (Save 14 cycles
>> 346 => 332 cycles)
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>   arch/powerpc/kernel/entry_32.S | 1 -
>>   arch/powerpc/kernel/syscall.c  | 7 +++++--
>>   2 files changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
>> index 9922a04650f7..6ae9c7bcb06c 100644
>> --- a/arch/powerpc/kernel/entry_32.S
>> +++ b/arch/powerpc/kernel/entry_32.S
>> @@ -343,7 +343,6 @@ transfer_to_syscall:
>>   
>>   ret_from_syscall:
>>   	addi    r4,r1,STACK_FRAME_OVERHEAD
>> -	li	r5,0
>>   	bl	syscall_exit_prepare
>>   #if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
>>   	/* If the process has its own DBCR0 value, load it up.  The internal
>> diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
>> index 476909b11051..30f8a397a522 100644
>> --- a/arch/powerpc/kernel/syscall.c
>> +++ b/arch/powerpc/kernel/syscall.c
>> @@ -86,7 +86,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
>>   	local_irq_enable();
>>   
>>   	if (unlikely(current_thread_info()->flags & _TIF_SYSCALL_DOTRACE)) {
>> -		if (unlikely(regs->trap == 0x7ff0)) {
>> +		if (IS_ENABLED(CONFIG_PPC64) && unlikely(regs->trap == 0x7ff0)) {
>>   			/* Unsupported scv vector */
>>   			_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
>>   			return regs->gpr[3];
>> @@ -109,7 +109,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
>>   		r8 = regs->gpr[8];
>>   
>>   	} else if (unlikely(r0 >= NR_syscalls)) {
>> -		if (unlikely(regs->trap == 0x7ff0)) {
>> +		if (IS_ENABLED(CONFIG_PPC64) && unlikely(regs->trap == 0x7ff0)) {
> 
> Perhaps this could be hidden behind a function like trap_is_scv()?
> 
> trap_is_unsupported_scv() ?
> 

Ok, I did that in v5

Thanks
Christophe