linux-kernel - Re: [RFC PATCH 1/1] riscv: Improve arch_get_mmap

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Date: Fri, 22 Dec 2023 19:48:36 +0800
From: Guo Ren <guoren@...nel.org>
To: Leonardo Bras <leobras@...hat.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Björn Töpel <bjorn@...osinc.com>, 
	Conor Dooley <conor.dooley@...rochip.com>, Vincent Chen <vincent.chen@...ive.com>, 
	Andy Chiu <andy.chiu@...ive.com>, Charlie Jenkins <charlie@...osinc.com>, 
	Clément Léger <cleger@...osinc.com>, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] riscv: Improve arch_get_mmap_end() macro

On Fri, Dec 22, 2023 at 4:27 PM Leonardo Bras <leobras@...hat.com> wrote:
>
> This macro caused me some confusion, which took some reviewer's time to
> make it clear, so I propose adding a short comment in code to avoid
> confusion in the future.
>
> Also, added some improvements to the macro, such as removing the
> assumption of VA_USER_SV57 being the largest address space.
>
> Signed-off-by: Leonardo Bras <leobras@...hat.com>
> ---
>  arch/riscv/include/asm/processor.h | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index f19f861cda549..2278e2a8362af 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -18,15 +18,21 @@
>  #define DEFAULT_MAP_WINDOW     (UL(1) << (MMAP_VA_BITS - 1))
>  #define STACK_TOP_MAX          TASK_SIZE_64
>
> +/*
> + * addr is a hint to the maximum userspace address that mmap should provide, so
> + * this macro needs to return the largest address space available so that
> + * mmap_end < addr, being mmap_end the top of that address space.
> + * See Documentation/arch/riscv/vm-layout.rst for more details.
> + */
>  #define arch_get_mmap_end(addr, len, flags)                    \
>  ({                                                             \
>         unsigned long mmap_end;                                 \
>         typeof(addr) _addr = (addr);                            \
>         if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
>                 mmap_end = STACK_TOP_MAX;                       \
> -       else if ((_addr) >= VA_USER_SV57)                       \
> -               mmap_end = STACK_TOP_MAX;                       \
> -       else if ((((_addr) >= VA_USER_SV48)) && (VA_BITS >= VA_BITS_SV48)) \
> +       else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
> +               mmap_end = VA_USER_SV57;                        \
It's clearer.

LGTM.
Reviewed-by: Guo Ren <guoren@...nel.org>

> +       else if (((_addr) >= VA_USER_SV48) && (VA_BITS >= VA_BITS_SV48)) \
>                 mmap_end = VA_USER_SV48;                        \
>         else                                                    \
>                 mmap_end = VA_USER_SV39;                        \
> --
> 2.43.0
>


-- 
Best Regards
 Guo Ren