linux-kernel - Re: [PATCH V2 4/4] riscv: mm: Optimize TASK

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Date: Fri, 22 Dec 2023 02:09:05 -0300
From: Leonardo Bras <leobras@...hat.com>
To: guoren@...nel.org
Cc: Leonardo Bras <leobras@...hat.com>,
	linux-kernel@...r.kernel.org,
	paul.walmsley@...ive.com,
	palmer@...belt.com,
	alexghiti@...osinc.com,
	charlie@...osinc.com,
	xiao.w.wang@...el.com,
	david@...hat.com,
	panqinglin2020@...as.ac.cn,
	rick.p.edgecombe@...el.com,
	willy@...radead.org,
	bjorn@...osinc.com,
	conor.dooley@...rochip.com,
	cleger@...osinc.com,
	linux-riscv@...ts.infradead.org,
	Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V2 4/4] riscv: mm: Optimize TASK_SIZE definition

On Thu, Dec 21, 2023 at 10:47:01AM -0500, guoren@...nel.org wrote:
> From: Guo Ren <guoren@...ux.alibaba.com>
> 
> Unify the TASK_SIZE definition with VA_BITS for better readability.
> Add COMPAT mode user address space info in the comment.
> 
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> ---
>  arch/riscv/include/asm/pgtable.h | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index e415582276ec..d165ddae3b42 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -866,6 +866,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
>   * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
>   * Task size is:
>   * -        0x9fc00000	(~2.5GB) for RV32.
> + * -        0x80000000	(   2GB) for RV64 compat mode
>   * -      0x4000000000	( 256GB) for RV64 using SV39 mmu
>   * -    0x800000000000	( 128TB) for RV64 using SV48 mmu
>   * - 0x100000000000000	(  64PB) for RV64 using SV57 mmu
> @@ -877,11 +878,11 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
>   * Similarly for SV57, bits 63–57 must be equal to bit 56.
>   */
>  #ifdef CONFIG_64BIT
> -#define TASK_SIZE_64	(PGDIR_SIZE * PTRS_PER_PGD / 2)
> +#define TASK_SIZE_64	(UL(1) << (VA_BITS - 1))

Checked for l5, l4 and l3, and it seems a correct replacement.

>  
>  #ifdef CONFIG_COMPAT
> -#define TASK_SIZE_32	(_AC(0x80000000, UL))
> -#define TASK_SIZE	(test_thread_flag(TIF_32BIT) ? \
> +#define TASK_SIZE_32	(UL(1) << (VA_BITS_SV32 - 1))

Oh, much better. Thanks for removing the magic number :)

> +#define TASK_SIZE	(is_compat_task() ? \
>  			 TASK_SIZE_32 : TASK_SIZE_64)
>  #else
>  #define TASK_SIZE	TASK_SIZE_64
> -- 
> 2.40.1
> 

That's much more readable IMO now. Thanks!

FWIW:
Reviewed-by: Leonardo Bras <leobras@...hat.com>