linux-kernel - Re: [PATCH v2 RESEND] LoongArch: Remove unused kernel stack padding

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Message-ID: <43126fe8-9040-a574-a149-273844d3073f@xen0n.name>
Date:   Wed, 26 Oct 2022 15:27:05 +0800
From:   WANG Xuerui <kernel@...0n.name>
To:     Jinyang He <hejinyang@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>
Cc:     Xi Ruoyao <xry111@...111.site>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 RESEND] LoongArch: Remove unused kernel stack padding

On 2022/10/26 11:55, Jinyang He wrote:
> Kernel stack padding looks like obey MIPS o32 Calling Convention, as
> LoongArch is inspired by MIPS and keep it. Remove it avoid not clear
> code.

Just some improvement to the commit message so it's clearer:

"The current LoongArch kernel stack is padded as if obeying the MIPS o32 
calling convention, signifying the port's MIPS lineage but no longer 
making sense. Remove the padding for clarity."

> 
> Link: https://lore.kernel.org/loongarch/1662130897-13156-1-git-send-email-hejinyang@loongson.cn/
> 

I think this blank line between the "Link" and S-o-b tags could be removed.

> Signed-off-by: Jinyang He <hejinyang@...ngson.cn>
> ---
> v2: Remove TOP_OF_KERNEL_STACK_PADDING
>      Remove 'init stack pointer' in head.S
> 
>   arch/loongarch/include/asm/processor.h | 2 +-
>   arch/loongarch/include/asm/ptrace.h    | 2 +-
>   arch/loongarch/kernel/head.S           | 3 +--
>   arch/loongarch/kernel/process.c        | 4 ++--
>   arch/loongarch/kernel/switch.S         | 2 +-
>   5 files changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/loongarch/include/asm/processor.h b/arch/loongarch/include/asm/processor.h
> index 6954dc5d24e9..7184f1dc61f2 100644
> --- a/arch/loongarch/include/asm/processor.h
> +++ b/arch/loongarch/include/asm/processor.h
> @@ -191,7 +191,7 @@ static inline void flush_thread(void)
>   unsigned long __get_wchan(struct task_struct *p);
>   
>   #define __KSTK_TOS(tsk) ((unsigned long)task_stack_page(tsk) + \
> -			 THREAD_SIZE - 32 - sizeof(struct pt_regs))
> +			 THREAD_SIZE - sizeof(struct pt_regs))
>   #define task_pt_regs(tsk) ((struct pt_regs *)__KSTK_TOS(tsk))
>   #define KSTK_EIP(tsk) (task_pt_regs(tsk)->csr_era)
>   #define KSTK_ESP(tsk) (task_pt_regs(tsk)->regs[3])
> diff --git a/arch/loongarch/include/asm/ptrace.h b/arch/loongarch/include/asm/ptrace.h
> index 7437b9366c3b..59c4608de91d 100644
> --- a/arch/loongarch/include/asm/ptrace.h
> +++ b/arch/loongarch/include/asm/ptrace.h
> @@ -133,7 +133,7 @@ static inline void die_if_kernel(const char *str, struct pt_regs *regs)
>   #define current_pt_regs()						\
>   ({									\
>   	unsigned long sp = (unsigned long)__builtin_frame_address(0);	\
> -	(struct pt_regs *)((sp | (THREAD_SIZE - 1)) + 1 - 32) - 1;	\
> +	(struct pt_regs *)((sp | (THREAD_SIZE - 1)) + 1) - 1;		\
>   })
>   
>   /* Helpers for working with the user stack pointer */
> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
> index 97425779ce9f..84970e266658 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -84,10 +84,9 @@ SYM_CODE_START(kernel_entry)			# kernel entry point
>   
>   	la.pcrel	tp, init_thread_union
>   	/* Set the SP after an empty pt_regs.  */
> -	PTR_LI		sp, (_THREAD_SIZE - 32 - PT_SIZE)
> +	PTR_LI		sp, (_THREAD_SIZE - PT_SIZE)
>   	PTR_ADD		sp, sp, tp
>   	set_saved_sp	sp, t0, t1
> -	PTR_ADDI	sp, sp, -4 * SZREG	# init stack pointer
>   
>   	bl		start_kernel
>   	ASM_BUG()
> diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/process.c
> index 1256e3582475..2526b68f1c0f 100644
> --- a/arch/loongarch/kernel/process.c
> +++ b/arch/loongarch/kernel/process.c
> @@ -129,7 +129,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
>   	unsigned long clone_flags = args->flags;
>   	struct pt_regs *childregs, *regs = current_pt_regs();
>   
> -	childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE - 32;
> +	childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
>   
>   	/* set up new TSS. */
>   	childregs = (struct pt_regs *) childksp - 1;
> @@ -236,7 +236,7 @@ bool in_task_stack(unsigned long stack, struct task_struct *task,
>   			struct stack_info *info)
>   {
>   	unsigned long begin = (unsigned long)task_stack_page(task);
> -	unsigned long end = begin + THREAD_SIZE - 32;
> +	unsigned long end = begin + THREAD_SIZE;
>   
>   	if (stack < begin || stack >= end)
>   		return false;
> diff --git a/arch/loongarch/kernel/switch.S b/arch/loongarch/kernel/switch.S
> index 43ebbc3990f7..202a163cb32f 100644
> --- a/arch/loongarch/kernel/switch.S
> +++ b/arch/loongarch/kernel/switch.S
> @@ -26,7 +26,7 @@ SYM_FUNC_START(__switch_to)
>   	move	tp, a2
>   	cpu_restore_nonscratch a1
>   
> -	li.w		t0, _THREAD_SIZE - 32
> +	li.w		t0, _THREAD_SIZE
>   	PTR_ADD		t0, t0, tp
>   	set_saved_sp	t0, t1, t2
>   

Otherwise LGTM, assuming you have tested it before sending (I don't 
currently have the capacity to immediately test this for you)...

Reviewed-by: WANG Xuerui <git@...0n.name>


-- 
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/