linux-kernel - Re: [PATCH V4 8/8] riscv: Add config of thread stack size

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Date:   Tue, 20 Sep 2022 09:15:12 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     guoren <guoren@...nel.org>
Cc:     "Palmer Dabbelt" <palmer@...osinc.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Andy Lutomirski" <luto@...nel.org>,
        "Conor.Dooley" <conor.dooley@...rochip.com>,
        Heiko Stübner <heiko@...ech.de>,
        "Jisheng Zhang" <jszhang@...nel.org>, lazyparser@...il.com,
        falcon@...ylab.org, "Huacai Chen" <chenhuacai@...nel.org>,
        "Anup Patel" <apatel@...tanamicro.com>,
        "Atish Patra" <atishp@...shpatra.org>,
        "Palmer Dabbelt" <palmer@...belt.com>,
        "Paul Walmsley" <paul.walmsley@...ive.com>,
        "Sebastian Andrzej Siewior" <bigeasy@...utronix.de>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        "Guo Ren" <guoren@...ux.alibaba.com>,
        "Andreas Schwab" <schwab@...e.de>
Subject: Re: [PATCH V4 8/8] riscv: Add config of thread stack size

On Tue, Sep 20, 2022, at 2:46 AM, Guo Ren wrote:

>
> How about this one: (only THREAD_SIZE, no THREAD_ORDER&SHIFT.)
>
> -
>  /* thread information allocation */
> -#ifdef CONFIG_64BIT
> -#define THREAD_SIZE_ORDER      (2 + KASAN_STACK_ORDER)
> -#else
> -#define THREAD_SIZE_ORDER      (1 + KASAN_STACK_ORDER)
> -#endif
> -#define THREAD_SIZE            (PAGE_SIZE << THREAD_SIZE_ORDER)
> +#define THREAD_SIZE            CONFIG_THREAD_SIZE


So far looks fine.

>
>  /*
>   * By aligning VMAP'd stacks to 2 * THREAD_SIZE, we can detect overflow by
> - * checking sp & (1 << THREAD_SHIFT), which we can do cheaply in the entry
> - * assembly.
> + * checking sp & THREAD_SIZE, which we can do cheaply in the entry assembly.
>   */
>  #ifdef CONFIG_VMAP_STACK
>  #define THREAD_ALIGN            (2 * THREAD_SIZE)
> @@ -36,7 +24,6 @@
>  #define THREAD_ALIGN            THREAD_SIZE
>  #endif

The THREAD_ALIGN does not, this only works for power-of-two numbers of
THREAD_SIZE, 

> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 426529b84db0..1e35fb3bdae5 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -29,8 +29,8 @@ _restore_kernel_tpsp:
>
>  #ifdef CONFIG_VMAP_STACK
>         addi sp, sp, -(PT_SIZE_ON_STACK)
> -       srli sp, sp, THREAD_SHIFT
> -       andi sp, sp, 0x1
> +       srli sp, sp, PAGE_SHIFT
> +       andi sp, sp, (THREAD_SIZE >> PAGE_SHIFT)

I think this needs to use THREAD_ALIGN, not THREAD_SIZE.

      Arnd