linux-kernel - Re: [PATCH] riscv: Correct the MODULES

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Date:   Tue, 1 Aug 2023 14:05:39 +0200
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     Song Shuai <suagrfillet@...il.com>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, akpm@...ux-foundation.org,
        guoren@...nel.org, sergey.matyukevich@...tacore.com,
        david@...hat.com, wangkefeng.wang@...wei.com,
        panqinglin2020@...as.ac.cn, woodrow.shen@...ive.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Correct the MODULES_VADDR

Hi Song,

On Tue, Aug 1, 2023 at 1:10 PM Song Shuai <suagrfillet@...il.com> wrote:
>
> As Documentation/riscv/vm-layout.rst describes, the 2G-sized "modules, BPF"
> area should lie right before the "kernel" area. But the current definition
> of MODULES_VADDR isn't consistent with that, so correct it.
>
> Before this patch, the size of "modules" from print_vm_layout() is not 2G.
>
> [    0.000000]      modules : 0xffffffff2ff2f000 - 0xffffffffae600000 (2022 MB)
> [    0.000000]       lowmem : 0xff60000000000000 - 0xff60000040000000 (1024 MB)
> [    0.000000]       kernel : 0xffffffffae600000 - 0xffffffffffffffff (1305 MB)
>
> After this patch, the size is 2G.
>
> [    0.000000]      modules : 0xffffffff3a000000 - 0xffffffffba000000 (2048 MB)
> [    0.000000]       lowmem : 0xff60000000000000 - 0xff60000040000000 (1024 MB)
> [    0.000000]       kernel : 0xffffffffba000000 - 0xffffffffffffffff (1119 MB)
>
> Signed-off-by: Song Shuai <suagrfillet@...il.com>
> ---
>  arch/riscv/include/asm/pgtable.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 75970ee2bda2..7c57e17fc758 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -53,8 +53,8 @@
>  #ifdef CONFIG_64BIT
>  /* This is used to define the end of the KASAN shadow region */
>  #define MODULES_LOWEST_VADDR   (KERNEL_LINK_ADDR - SZ_2G)
> -#define MODULES_VADDR          (PFN_ALIGN((unsigned long)&_end) - SZ_2G)
>  #define MODULES_END            (PFN_ALIGN((unsigned long)&_start))
> +#define MODULES_VADDR          (MODULES_END - SZ_2G)
>  #endif
>
>  /*
> --
> 2.20.1
>

The documentation is approximative, the modules must stay within a 2GB
window to *all* the kernel symbols, hence the __end - 2G, not __start.