Re: [PATCH v5] powerpc/irq: inline call_do_irq() and call_do_softirq() on PPC32

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Hi Michael,

Le 07/12/2019 à 18:20, Christophe Leroy a écrit :
> call_do_irq() and call_do_softirq() are simple enough to be
> worth inlining.
> 
> Inlining them avoids an mflr/mtlr pair plus a save/reload on stack.
> It also allows GCC to keep the saved ksp_limit in an nonvolatile reg.
> 
> This is inspired from S390 arch. Several other arches do more or
> less the same. The way sparc arch does seems odd thought.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>

Anything more I need to do for this patch to get merged ?

Thanks
Christophe


> 
> ---
> v2: no change.
> v3: no change.
> v4:
> - comment reminding the purpose of the inline asm block.
> - added r2 as clobbered reg
> v5:
> - Limiting the change to PPC32 for now.
> - removed r2 from the clobbered regs list (on PPC32 r2 points to current all the time)
> - Removed patch 1 and merged ksp_limit handling in here.
> ---
>   arch/powerpc/include/asm/irq.h |  2 ++
>   arch/powerpc/kernel/irq.c      | 48 ++++++++++++++++++++++++++++++++++++++++++
>   arch/powerpc/kernel/misc_32.S  | 39 ----------------------------------
>   3 files changed, 50 insertions(+), 39 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/irq.h b/arch/powerpc/include/asm/irq.h
> index 814dfab7e392..e4a92f0b4ad4 100644
> --- a/arch/powerpc/include/asm/irq.h
> +++ b/arch/powerpc/include/asm/irq.h
> @@ -56,8 +56,10 @@ extern void *mcheckirq_ctx[NR_CPUS];
>   extern void *hardirq_ctx[NR_CPUS];
>   extern void *softirq_ctx[NR_CPUS];
>   
> +#ifdef CONFIG_PPC64
>   void call_do_softirq(void *sp);
>   void call_do_irq(struct pt_regs *regs, void *sp);
> +#endif
>   extern void do_IRQ(struct pt_regs *regs);
>   extern void __init init_IRQ(void);
>   extern void __do_irq(struct pt_regs *regs);
> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
> index 5645bc9cbc09..240eca12c71d 100644
> --- a/arch/powerpc/kernel/irq.c
> +++ b/arch/powerpc/kernel/irq.c
> @@ -611,6 +611,54 @@ static inline void check_stack_overflow(void)
>   #endif
>   }
>   
> +#ifdef CONFIG_PPC32
> +static inline void call_do_softirq(const void *sp)
> +{
> +	register unsigned long ret asm("r3");
> +	unsigned long limit = current->thread.ksp_limit;
> +
> +	/* Adjust the stack limit */
> +	current->thread.ksp_limit = (unsigned long)sp;
> +
> +	/* Temporarily switch r1 to sp, call __do_softirq() then restore r1. */
> +	asm volatile(
> +		"	"PPC_STLU"	1, %2(%1);\n"
> +		"	mr		1, %1;\n"
> +		"	bl		%3;\n"
> +		"	"PPC_LL"	1, 0(1);\n" :
> +		"=r"(ret) :
> +		"b"(sp), "i"(THREAD_SIZE - STACK_FRAME_OVERHEAD), "i"(__do_softirq) :
> +		"lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", "cr7",
> +		"r0", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12");
> +
> +	/* Restore stack limit */
> +	current->thread.ksp_limit = limit;
> +}
> +
> +static inline void call_do_irq(struct pt_regs *regs, void *sp)
> +{
> +	register unsigned long r3 asm("r3") = (unsigned long)regs;
> +	unsigned long limit = current->thread.ksp_limit;
> +
> +	/* Adjust the stack limit */
> +	current->thread.ksp_limit = (unsigned long)sp;
> +
> +	/* Temporarily switch r1 to sp, call __do_irq() then restore r1 */
> +	asm volatile(
> +		"	"PPC_STLU"	1, %2(%1);\n"
> +		"	mr		1, %1;\n"
> +		"	bl		%3;\n"
> +		"	"PPC_LL"	1, 0(1);\n" :
> +		"+r"(r3) :
> +		"b"(sp), "i"(THREAD_SIZE - STACK_FRAME_OVERHEAD), "i"(__do_irq) :
> +		"lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", "cr7",
> +		"r0", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12");
> +
> +	/* Restore stack limit */
> +	current->thread.ksp_limit = limit;
> +}
> +#endif
> +
>   void __do_irq(struct pt_regs *regs)
>   {
>   	unsigned int irq;
> diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
> index d80212be8698..341a3cd199cb 100644
> --- a/arch/powerpc/kernel/misc_32.S
> +++ b/arch/powerpc/kernel/misc_32.S
> @@ -28,45 +28,6 @@
>   	.text
>   
>   /*
> - * We store the saved ksp_limit in the unused part
> - * of the STACK_FRAME_OVERHEAD
> - */
> -_GLOBAL(call_do_softirq)
> -	mflr	r0
> -	stw	r0,4(r1)
> -	lwz	r10,THREAD+KSP_LIMIT(r2)
> -	stw	r3, THREAD+KSP_LIMIT(r2)
> -	stwu	r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3)
> -	mr	r1,r3
> -	stw	r10,8(r1)
> -	bl	__do_softirq
> -	lwz	r10,8(r1)
> -	lwz	r1,0(r1)
> -	lwz	r0,4(r1)
> -	stw	r10,THREAD+KSP_LIMIT(r2)
> -	mtlr	r0
> -	blr
> -
> -/*
> - * void call_do_irq(struct pt_regs *regs, void *sp);
> - */
> -_GLOBAL(call_do_irq)
> -	mflr	r0
> -	stw	r0,4(r1)
> -	lwz	r10,THREAD+KSP_LIMIT(r2)
> -	stw	r4, THREAD+KSP_LIMIT(r2)
> -	stwu	r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4)
> -	mr	r1,r4
> -	stw	r10,8(r1)
> -	bl	__do_irq
> -	lwz	r10,8(r1)
> -	lwz	r1,0(r1)
> -	lwz	r0,4(r1)
> -	stw	r10,THREAD+KSP_LIMIT(r2)
> -	mtlr	r0
> -	blr
> -
> -/*
>    * This returns the high 64 bits of the product of two 64-bit numbers.
>    */
>   _GLOBAL(mulhdu)
>