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Date: Sun, 4 Sep 2022 20:19:20 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Jinyang He <hejinyang@...ngson.cn>
Cc: WANG Xuerui <kernel@...0n.name>, Oleg Nesterov <oleg@...hat.com>,
loongarch@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] LoongArch: Mark kernel stack padding as TOP_OF_KERNEL_STACK_PADDING
Hi, Jinyang,
I don't know what scenarios this padding is used and how to use. And
in x86 there is only TOP_OF_KERNEL_STACK_PADDING but we need
TOP_OF_KERNEL_STACK_PADDING and _TOP_OF_KERNEL_STACK_PADDING. Two
macros are hard to maintain.
Huacai
On Fri, Sep 2, 2022 at 11:01 PM Jinyang He <hejinyang@...ngson.cn> wrote:
>
> Mark the top reserved bytes of the kernel stack by a macro. It collects
> that info so that we can modify or discarded (let it be 0) this padding
> if needed. Its name is referenced from x86_64. It seems that x86_64
> think the padding as extension on top of the kernel stack in other mode
> (normally the top is only pt_regs). Although LoongArch not produce
> such an extension at present, collect them because of the uncertainty
> of the future. Note that this patch does not modify macro size. It
> requires another strict evaluation.
>
> Signed-off-by: Jinyang He <hejinyang@...ngson.cn>
> ---
> arch/loongarch/include/asm/processor.h | 3 ++-
> arch/loongarch/include/asm/ptrace.h | 3 ++-
> arch/loongarch/include/asm/stackframe.h | 1 +
> arch/loongarch/kernel/head.S | 2 +-
> arch/loongarch/kernel/process.c | 4 ++--
> arch/loongarch/kernel/switch.S | 2 +-
> 6 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/processor.h b/arch/loongarch/include/asm/processor.h
> index 1c4b43083..6077fd8e3 100644
> --- a/arch/loongarch/include/asm/processor.h
> +++ b/arch/loongarch/include/asm/processor.h
> @@ -193,8 +193,9 @@ static inline void flush_thread(void)
>
> unsigned long __get_wchan(struct task_struct *p);
>
> +#define TOP_OF_KERNEL_STACK_PADDING 32
> #define __KSTK_TOS(tsk) ((unsigned long)task_stack_page(tsk) + \
> - THREAD_SIZE - 32 - sizeof(struct pt_regs))
> + THREAD_SIZE - TOP_OF_KERNEL_STACK_PADDING - 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 17838c6b7..cdceeaa60 100644
> --- a/arch/loongarch/include/asm/ptrace.h
> +++ b/arch/loongarch/include/asm/ptrace.h
> @@ -133,7 +133,8 @@ 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 - \
> + TOP_OF_KERNEL_STACK_PADDING) - 1; \
> })
>
> /* Helpers for working with the user stack pointer */
> diff --git a/arch/loongarch/include/asm/stackframe.h b/arch/loongarch/include/asm/stackframe.h
> index 4ca953062..e9f849b29 100644
> --- a/arch/loongarch/include/asm/stackframe.h
> +++ b/arch/loongarch/include/asm/stackframe.h
> @@ -216,4 +216,5 @@
> RESTORE_SP_AND_RET \docfi
> .endm
>
> +#define _TOP_OF_KERNEL_STACK_PADDING 32
> #endif /* _ASM_STACKFRAME_H */
> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
> index eb3f641d5..290c53847 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -75,7 +75,7 @@ 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 - _TOP_OF_KERNEL_STACK_PADDING - PT_SIZE)
> PTR_ADD sp, sp, tp
> set_saved_sp sp, t0, t1
> PTR_ADDI sp, sp, -4 * SZREG # init stack pointer
> diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/process.c
> index 660492f06..b51cf7975 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 - TOP_OF_KERNEL_STACK_PADDING;
>
> /* 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 - TOP_OF_KERNEL_STACK_PADDING;
>
> if (stack < begin || stack >= end)
> return false;
> diff --git a/arch/loongarch/kernel/switch.S b/arch/loongarch/kernel/switch.S
> index 43ebbc399..1797aceae 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 - _TOP_OF_KERNEL_STACK_PADDING
> PTR_ADD t0, t0, tp
> set_saved_sp t0, t1, t2
>
> --
> 2.31.1
>
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