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* [PATCH v2 RESEND] LoongArch: Remove unused kernel stack padding
@ 2022-10-26  3:55 Jinyang He
  2022-10-26  7:27 ` WANG Xuerui
  0 siblings, 1 reply; 4+ messages in thread
From: Jinyang He @ 2022-10-26  3:55 UTC (permalink / raw)
  To: Huacai Chen, WANG Xuerui, Oleg Nesterov
  Cc: Xi Ruoyao, loongarch, linux-kernel

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.

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

Signed-off-by: Jinyang He <hejinyang@loongson.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
 
-- 
2.34.3


^ permalink raw reply related	[flat|nested] 4+ messages in thread
* Re: [PATCH v2 RESEND] LoongArch: Remove unused kernel stack padding
  2022-10-26  3:55 [PATCH v2 RESEND] LoongArch: Remove unused kernel stack padding Jinyang He
@ 2022-10-26  7:27 ` WANG Xuerui
  2022-10-26 13:24   ` Jinyang He
  0 siblings, 1 reply; 4+ messages in thread
From: WANG Xuerui @ 2022-10-26  7:27 UTC (permalink / raw)
  To: Jinyang He, Huacai Chen, Oleg Nesterov; +Cc: Xi Ruoyao, loongarch, linux-kernel

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@loongson.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@xen0n.name>


-- 
WANG "xen0n" Xuerui

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


^ permalink raw reply	[flat|nested] 4+ messages in thread
* Re: [PATCH v2 RESEND] LoongArch: Remove unused kernel stack padding
  2022-10-26  7:27 ` WANG Xuerui
@ 2022-10-26 13:24   ` Jinyang He
  2022-10-26 13:27     ` WANG Xuerui
  0 siblings, 1 reply; 4+ messages in thread
From: Jinyang He @ 2022-10-26 13:24 UTC (permalink / raw)
  To: WANG Xuerui, Huacai Chen, Oleg Nesterov
  Cc: Xi Ruoyao, loongarch, linux-kernel

Hi, Xuerui,


在 2022/10/26 15:27, WANG Xuerui 写道:
> 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."

Thanks, I'll improve it and send it later.


>
>>
>> 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.

Ok.


>
>> Signed-off-by: Jinyang He <hejinyang@loongson.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@xen0n.name>


Emm, to be honest, I didn't do tests like LTP. I ususally do development
on CLFS-LoongArch while kernel has this patch. And it works normally.


Thanks,

Jinyang


^ permalink raw reply	[flat|nested] 4+ messages in thread
* Re: [PATCH v2 RESEND] LoongArch: Remove unused kernel stack padding
  2022-10-26 13:24   ` Jinyang He
@ 2022-10-26 13:27     ` WANG Xuerui
  0 siblings, 0 replies; 4+ messages in thread
From: WANG Xuerui @ 2022-10-26 13:27 UTC (permalink / raw)
  To: Jinyang He, Huacai Chen, Oleg Nesterov; +Cc: Xi Ruoyao, loongarch, linux-kernel

On 2022/10/26 21:24, Jinyang He wrote:
> Emm, to be honest, I didn't do tests like LTP. I ususally do development
> on CLFS-LoongArch while kernel has this patch. And it works normally.

For changes touching fundamental parts that make the system work at all, 
like this, "it continues to boot and work" usually is enough for 
confirming correctness. Although some harder test runs would certainly 
be better ;-)

-- 
WANG "xen0n" Xuerui

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


^ permalink raw reply	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-10-26 13:28 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2022-10-26  3:55 [PATCH v2 RESEND] LoongArch: Remove unused kernel stack padding Jinyang He
2022-10-26  7:27 ` WANG Xuerui
2022-10-26 13:24   ` Jinyang He
2022-10-26 13:27     ` WANG Xuerui

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