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

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Date:   Tue, 26 Jan 2021 20:16:39 +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>, 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

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() ?

Thanks,
Nick