linux-kernel - Re: [PATCH v3] LoongArch: Remove unused kernel stack padding

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Message-ID: <CAAhV-H7DOKx4CzPZDgYVHF-zZ8j9NY6CesZCGvtc+_fqoWrXRQ@mail.gmail.com>
Date:   Thu, 27 Oct 2022 20:50:45 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Jinyang He <hejinyang@...ngson.cn>
Cc:     WANG Xuerui <kernel@...0n.name>, Oleg Nesterov <oleg@...hat.com>,
        Xi Ruoyao <xry111@...111.site>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, WANG Xuerui <git@...0n.name>
Subject: Re: [PATCH v3] LoongArch: Remove unused kernel stack padding

Queued for loongarch-next, thanks.

Huacai

On Thu, Oct 27, 2022 at 7:12 PM Jinyang He <hejinyang@...ngson.cn> wrote:
>
> 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/
> Reviewed-by: WANG Xuerui <git@...0n.name>
> Signed-off-by: Jinyang He <hejinyang@...ngson.cn>
> ---
> v2: Remove TOP_OF_KERNEL_STACK_PADDING
>     Remove 'init stack pointer' in head.S
> v3: Improve commit message suggested by Xuerui
>     Add Reviewed-by tags
>
>  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
>
> --
> 2.34.3
>