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Message-ID: <CAAhV-H7RSn2ek5CeLnohTcrh=0unDNmaLDq+yDH2oqshoeRMNQ@mail.gmail.com>
Date: Fri, 24 Jan 2025 17:05:21 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>,
WANG Xuerui <kernel@...0n.name>, Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>,
Alexandre Ghiti <alexghiti@...osinc.com>, linux-riscv@...ts.infradead.org,
linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev
Subject: Re: [PATCH v2 3/4] loongarch: entry: Migrate ret_from_fork() to C
Hi, Charlie,
On Fri, Jan 24, 2025 at 3:15 AM Charlie Jenkins <charlie@...osinc.com> wrote:
>
> Loongarch is the only architecture that calls
We usually use "LoongArch" instead of "loongarch" or "Loongarch".
> syscall_exit_to_user_mode() from asm. Move the call into C so that this
> function can be inlined across all architectures.
>
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> ---
> arch/loongarch/include/asm/asm-prototypes.h | 5 +++++
> arch/loongarch/include/asm/switch_to.h | 8 +++++++
> arch/loongarch/kernel/entry.S | 22 +++++++++----------
> arch/loongarch/kernel/process.c | 34 ++++++++++++++++++++++++-----
> 4 files changed, 51 insertions(+), 18 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/asm-prototypes.h b/arch/loongarch/include/asm/asm-prototypes.h
> index 51f224bcfc654228ae423e9a066b25b35102a5b9..0195d4309fd29f94664d5f34247198c769033b1b 100644
> --- a/arch/loongarch/include/asm/asm-prototypes.h
> +++ b/arch/loongarch/include/asm/asm-prototypes.h
> @@ -12,3 +12,8 @@ __int128_t __ashlti3(__int128_t a, int b);
> __int128_t __ashrti3(__int128_t a, int b);
> __int128_t __lshrti3(__int128_t a, int b);
> #endif
> +
> +asmlinkage void noinstr __no_stack_protector ret_from_kernel_thread(struct task_struct *prev,
> + struct pt_regs *regs,
> + int (*fn)(void *),
> + void *fn_arg);
It is a little strange that we only need to declare
ret_from_kernel_thread() but not ret_from_fork().
> diff --git a/arch/loongarch/include/asm/switch_to.h b/arch/loongarch/include/asm/switch_to.h
> index 5b225aff3ba21aa06d0713bc8e73e1b941389630..a1c5576f1fd145670e13038bec6dd390486099ab 100644
> --- a/arch/loongarch/include/asm/switch_to.h
> +++ b/arch/loongarch/include/asm/switch_to.h
> @@ -26,6 +26,14 @@ extern asmlinkage struct task_struct *__switch_to(struct task_struct *prev,
> struct task_struct *next, struct thread_info *next_ti,
> void *sched_ra, void *sched_cfa);
>
> +void noinstr __no_stack_protector ret_from_kernel_thread(struct task_struct *prev,
> + struct pt_regs *regs,
> + int (*fn)(void *),
> + void *fn_arg);
> +
> +void noinstr __no_stack_protector ret_from_fork(struct task_struct *prev,
> + struct pt_regs *regs);
> +
I prefer alpha-betical order, which means put ret_from_fork() before
ret_from_kernel_thread().
> /*
> * For newly created kernel threads switch_to() will return to
> * ret_from_kernel_thread, newly created user threads to ret_from_fork.
> diff --git a/arch/loongarch/kernel/entry.S b/arch/loongarch/kernel/entry.S
> index 48e7e34e355e83eae8165957ba2eac05a8bf17df..2abc29e573810e000f2fef4646ddca0dbb80eabe 100644
> --- a/arch/loongarch/kernel/entry.S
> +++ b/arch/loongarch/kernel/entry.S
> @@ -77,24 +77,22 @@ SYM_CODE_START(handle_syscall)
> SYM_CODE_END(handle_syscall)
> _ASM_NOKPROBE(handle_syscall)
>
> -SYM_CODE_START(ret_from_fork)
> +SYM_CODE_START(ret_from_fork_asm)
> UNWIND_HINT_REGS
> - bl schedule_tail # a0 = struct task_struct *prev
> - move a0, sp
> - bl syscall_exit_to_user_mode
> + move a1, sp
> + bl ret_from_fork
> RESTORE_STATIC
> RESTORE_SOME
> RESTORE_SP_AND_RET
> -SYM_CODE_END(ret_from_fork)
> +SYM_CODE_END(ret_from_fork_asm)
>
> -SYM_CODE_START(ret_from_kernel_thread)
> +SYM_CODE_START(ret_from_kernel_thread_asm)
> UNWIND_HINT_REGS
> - bl schedule_tail # a0 = struct task_struct *prev
> - move a0, s1
> - jirl ra, s0, 0
> - move a0, sp
> - bl syscall_exit_to_user_mode
> + move a1, sp
> + move a2, s0
> + move a3, s1
> + bl ret_from_kernel_thread
> RESTORE_STATIC
> RESTORE_SOME
> RESTORE_SP_AND_RET
> -SYM_CODE_END(ret_from_kernel_thread)
> +SYM_CODE_END(ret_from_kernel_thread_asm)
> diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/process.c
> index 6e58f65455c7ca3eae2e88ed852c8655a6701e5c..16cc949fe43443d70f1d865ce04595c2d8c1615b 100644
> --- a/arch/loongarch/kernel/process.c
> +++ b/arch/loongarch/kernel/process.c
> @@ -14,6 +14,7 @@
> #include <linux/init.h>
> #include <linux/kernel.h>
> #include <linux/errno.h>
> +#include <linux/entry-common.h>
> #include <linux/sched.h>
> #include <linux/sched/debug.h>
> #include <linux/sched/task.h>
> @@ -33,6 +34,7 @@
> #include <linux/prctl.h>
> #include <linux/nmi.h>
>
> +#include <asm/asm-prototypes.h>
> #include <asm/asm.h>
> #include <asm/bootinfo.h>
> #include <asm/cpu.h>
> @@ -47,6 +49,7 @@
> #include <asm/pgtable.h>
> #include <asm/processor.h>
> #include <asm/reg.h>
> +#include <asm/switch_to.h>
> #include <asm/unwind.h>
> #include <asm/vdso.h>
>
> @@ -63,8 +66,9 @@ EXPORT_SYMBOL(__stack_chk_guard);
> unsigned long boot_option_idle_override = IDLE_NO_OVERRIDE;
> EXPORT_SYMBOL(boot_option_idle_override);
>
> -asmlinkage void ret_from_fork(void);
> -asmlinkage void ret_from_kernel_thread(void);
> +asmlinkage void restore_and_ret(void);
> +asmlinkage void ret_from_fork_asm(void);
> +asmlinkage void ret_from_kernel_thread_asm(void);
>
> void start_thread(struct pt_regs *regs, unsigned long pc, unsigned long sp)
> {
> @@ -138,6 +142,24 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> return 0;
> }
>
> +asmlinkage void noinstr __no_stack_protector ret_from_kernel_thread(struct task_struct *prev,
> + struct pt_regs *regs,
> + int (*fn)(void *),
> + void *fn_arg)
> +{
> + schedule_tail(prev);
> +
> + fn(fn_arg);
> +
The two blank lines can be removed, and again, I prefer alpha-betical
order, which means put ret_from_fork() before
ret_from_kernel_thread().
Huacai
> + syscall_exit_to_user_mode(regs);
> +}
> +
> +void noinstr __no_stack_protector ret_from_fork(struct task_struct *prev, struct pt_regs *regs)
> +{
> + schedule_tail(prev);
> + syscall_exit_to_user_mode(regs);
> +}
> +
> /*
> * Copy architecture-specific thread state
> */
> @@ -165,8 +187,8 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
> p->thread.reg03 = childksp;
> p->thread.reg23 = (unsigned long)args->fn;
> p->thread.reg24 = (unsigned long)args->fn_arg;
> - p->thread.reg01 = (unsigned long)ret_from_kernel_thread;
> - p->thread.sched_ra = (unsigned long)ret_from_kernel_thread;
> + p->thread.reg01 = (unsigned long)ret_from_kernel_thread_asm;
> + p->thread.sched_ra = (unsigned long)ret_from_kernel_thread_asm;
> memset(childregs, 0, sizeof(struct pt_regs));
> childregs->csr_euen = p->thread.csr_euen;
> childregs->csr_crmd = p->thread.csr_crmd;
> @@ -182,8 +204,8 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
> childregs->regs[3] = usp;
>
> p->thread.reg03 = (unsigned long) childregs;
> - p->thread.reg01 = (unsigned long) ret_from_fork;
> - p->thread.sched_ra = (unsigned long) ret_from_fork;
> + p->thread.reg01 = (unsigned long) ret_from_fork_asm;
> + p->thread.sched_ra = (unsigned long) ret_from_fork_asm;
>
> /*
> * New tasks lose permission to use the fpu. This accelerates context
>
> --
> 2.43.0
>
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