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Date: Fri, 23 Sep 2022 17:43:33 +1000
Message-Id: <CN3M2A0W1J3A.2V3NYEDYLSIVQ@bobo>
From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Rohan McLure" <rmclure@linux.ibm.com>, <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH v6 20/25] powerpc: Change system_call_exception calling
 convention
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References: <20220921065605.1051927-1-rmclure@linux.ibm.com>
 <20220921065605.1051927-21-rmclure@linux.ibm.com>
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On Wed Sep 21, 2022 at 4:56 PM AEST, Rohan McLure wrote:
> Change system_call_exception arguments to pass a pointer to a stack frame
> container caller state, as well as the original r0, which determines the
> number of the syscall. This has been observed to yield improved performan=
ce
> to passing them by registers, circumventing the need to allocate a stack =
frame.
>
> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>

Thanks for splitting it out, I think it does make it nicer to review.

[...]

> diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.=
c
> index 15af0ed019a7..0e9ba3efee94 100644
> --- a/arch/powerpc/kernel/syscall.c
> +++ b/arch/powerpc/kernel/syscall.c
> @@ -13,9 +13,7 @@
> =20
> =20
>  /* Has to run notrace because it is entered not completely "reconciled" =
*/
> -notrace long system_call_exception(long r3, long r4, long r5,
> -				   long r6, long r7, long r8,
> -				   unsigned long r0, struct pt_regs *regs)
> +notrace long system_call_exception(struct pt_regs *regs, unsigned long r=
0)
>  {
>  	long ret;
>  	syscall_fn f;
> @@ -136,12 +134,6 @@ notrace long system_call_exception(long r3, long r4,=
 long r5,
>  		r0 =3D do_syscall_trace_enter(regs);
>  		if (unlikely(r0 >=3D NR_syscalls))
>  			return regs->gpr[3];
> -		r3 =3D regs->gpr[3];
> -		r4 =3D regs->gpr[4];
> -		r5 =3D regs->gpr[5];
> -		r6 =3D regs->gpr[6];
> -		r7 =3D regs->gpr[7];
> -		r8 =3D regs->gpr[8];
> =20
>  	} else if (unlikely(r0 >=3D NR_syscalls)) {
>  		if (unlikely(trap_is_unsupported_scv(regs))) {
> --=20
> 2.34.1

This is probably just missing the hunk

+       ret =3D f(regs->gpr[3], regs->gpr[4], regs->gpr[5],                =
                                                                           =
                                                                           =
       =20
+               regs->gpr[6], regs->gpr[7], regs->gpr[8]);       =20

which got into your next patch.

Otherwise I think it looks good.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>