linux-kernel - Re: [PATCH -next V8 06/14] riscv: convert to generic entry

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Message-ID: <874jua9lcp.fsf@all.your.base.are.belong.to.us>
Date:   Mon, 05 Dec 2022 11:49:10 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     guoren@...nel.org, arnd@...db.de, guoren@...nel.org,
        palmer@...osinc.com, tglx@...utronix.de, peterz@...radead.org,
        luto@...nel.org, conor.dooley@...rochip.com, heiko@...ech.de,
        jszhang@...nel.org, lazyparser@...il.com, falcon@...ylab.org,
        chenhuacai@...nel.org, apatel@...tanamicro.com,
        atishp@...shpatra.org, palmer@...belt.com,
        paul.walmsley@...ive.com, mark.rutland@....com,
        zouyipeng@...wei.com, bigeasy@...utronix.de,
        David.Laight@...lab.com, chenzhongjin@...wei.com,
        greentime.hu@...ive.com, andy.chiu@...ive.com
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH -next V8 06/14] riscv: convert to generic entry

guoren@...nel.org writes:

> From: Guo Ren <guoren@...ux.alibaba.com>
>
> This patch converts riscv to use the generic entry infrastructure from
> kernel/entry/*. The generic entry makes maintainers' work easier and
> codes more elegant. Here are the changes than before:
>
>  - More clear entry.S with handle_exception and ret_from_exception
>  - Get rid of complex custom signal implementation
>  - More readable syscall procedure
>  - Little modification on ret_from_fork & ret_from_kernel_thread
>  - Wrap with irqentry_enter/exit and syscall_enter/exit_from_user_mode
>  - Use the standard preemption code instead of custom
>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> Suggested-by: Huacai Chen <chenhuacai@...nel.org>
> Tested-by: Yipeng Zou <zouyipeng@...wei.com>
> ---

[...]

> diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
> index 5d3f2fbeb33c..c86d0eafdf6a 100644
> --- a/arch/riscv/kernel/sys_riscv.c
> +++ b/arch/riscv/kernel/sys_riscv.c
> @@ -5,8 +5,10 @@
>   * Copyright (C) 2017 SiFive
>   */
>  
> +#include <linux/entry-common.h>
>  #include <linux/syscalls.h>
>  #include <asm/unistd.h>
> +#include <asm/syscall.h>
>  #include <asm/cacheflush.h>
>  #include <asm-generic/mman-common.h>
>  
> @@ -69,3 +71,28 @@ SYSCALL_DEFINE3(riscv_flush_icache, uintptr_t, start, uintptr_t, end,
>  
>  	return 0;
>  }
> +
> +typedef long (*syscall_t)(ulong, ulong, ulong, ulong, ulong, ulong, ulong);
> +
> +asmlinkage void do_sys_ecall_u(struct pt_regs *regs)
> +{
> +	syscall_t syscall;
> +	ulong nr = regs->a7;
> +
> +	regs->epc += 4;
> +	regs->orig_a0 = regs->a0;
> +	regs->a0 = -ENOSYS;
> +
> +	nr = syscall_enter_from_user_mode(regs, nr);
> +#ifdef CONFIG_COMPAT
> +	if ((regs->status & SR_UXL) == SR_UXL_32)
> +		syscall = compat_sys_call_table[nr];
> +	else
> +#endif
> +		syscall = sys_call_table[nr];
> +
> +	if (nr < NR_syscalls)
> +		regs->a0 = syscall(regs->orig_a0, regs->a1, regs->a2,
> +				   regs->a3, regs->a4, regs->a5,
>  	regs->a6);

Now that we're doing the "pt_regs to call" dance, it would make sense to
introduce a syscall wrapper (like x86 and arm64) for riscv, so that we
don't need to unwrap all regs for all syscalls (See __MAP() in
include/linux/syscalls.h). That would be an optimization, so it could be
done as a follow-up, and not part of the series.


Björn