linux-kernel - Re: [PATCH 2/4] riscv: Fix loading 64-bit NOMMU kernels past the start of RAM

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Date: Tue, 27 Feb 2024 12:18:19 +0000
From: Conor Dooley <conor.dooley@...rochip.com>
To: Samuel Holland <samuel.holland@...ive.com>
CC: Palmer Dabbelt <palmer@...belt.com>, <linux-riscv@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] riscv: Fix loading 64-bit NOMMU kernels past the
 start of RAM

On Mon, Feb 26, 2024 at 04:34:47PM -0800, Samuel Holland wrote:
> commit 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the linear
> mapping") added logic to allow using RAM below the kernel load address.
> However, this does not work for NOMMU, where PAGE_OFFSET is fixed to the
> kernel load address. Since that range of memory corresponds to PFNs
> below ARCH_PFN_OFFSET, mm initialization runs off the beginning of
> mem_map and corrupts adjacent kernel memory. Fix this by restoring the
> previous behavior for NOMMU kernels.
> 
> Fixes: 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the linear mapping")

This commit was a year ago, why has nobody reported this as being an
issue before?

> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> ---
> 
>  arch/riscv/include/asm/page.h | 2 +-
>  arch/riscv/mm/init.c          | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 57e887bfa34c..94b3d6930fc3 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -89,7 +89,7 @@ typedef struct page *pgtable_t;
>  #define PTE_FMT "%08lx"
>  #endif
>  
> -#ifdef CONFIG_64BIT
> +#if defined(CONFIG_64BIT) && defined(CONFIG_MMU)
>  /*
>   * We override this value as its generic definition uses __pa too early in
>   * the boot process (before kernel_map.va_pa_offset is set).
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index fa34cf55037b..0c00efc75643 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -232,7 +232,7 @@ static void __init setup_bootmem(void)
>  	 * In 64-bit, any use of __va/__pa before this point is wrong as we
>  	 * did not know the start of DRAM before.
>  	 */
> -	if (IS_ENABLED(CONFIG_64BIT))
> +	if (IS_ENABLED(CONFIG_64BIT) && IS_ENABLED(CONFIG_MMU))
>  		kernel_map.va_pa_offset = PAGE_OFFSET - phys_ram_base;
>  
>  	/*
> -- 
> 2.43.0
> 

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