[PATCH 2/6] riscv: Allow NOMMU kernels to access all of RAM

[Jesse T]

On Sat, Oct 26, 2024 at 1:16 PM Samuel Holland
<samuel.holland at sifive.com> wrote:
>
> NOMMU kernels currently cannot access memory below the kernel link
> address. Remove this restriction by setting PAGE_OFFSET to the actual
> start of RAM, as determined from the devicetree. The kernel link address
> must be a constant, so keep using CONFIG_PAGE_OFFSET for that purpose.
>
> Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
Reviewed-by: Jesse Taube <mr.bossman075 at gmail.com>

> ---
>
>  arch/riscv/include/asm/page.h    | 12 ++++--------
>  arch/riscv/include/asm/pgtable.h |  2 +-
>  2 files changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 32d308a3355f..24d1ac052609 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -26,12 +26,9 @@
>   * When not using MMU this corresponds to the first free page in
>   * physical memory (aligned on a page boundary).
>   */
> -#ifdef CONFIG_64BIT
>  #ifdef CONFIG_MMU
> +#ifdef CONFIG_64BIT
>  #define PAGE_OFFSET            kernel_map.page_offset
> -#else
> -#define PAGE_OFFSET            _AC(CONFIG_PAGE_OFFSET, UL)
> -#endif
>  /*
>   * By default, CONFIG_PAGE_OFFSET value corresponds to SV57 address space so
>   * define the PAGE_OFFSET value for SV48 and SV39.
> @@ -41,6 +38,9 @@
>  #else
>  #define PAGE_OFFSET            _AC(CONFIG_PAGE_OFFSET, UL)
>  #endif /* CONFIG_64BIT */
> +#else
> +#define PAGE_OFFSET            ((unsigned long)phys_ram_base)
> +#endif /* CONFIG_MMU */
>
>  #ifndef __ASSEMBLY__
>
> @@ -97,11 +97,7 @@ typedef struct page *pgtable_t;
>  #define MIN_MEMBLOCK_ADDR      0
>  #endif
>
> -#ifdef CONFIG_MMU
>  #define ARCH_PFN_OFFSET                (PFN_DOWN((unsigned long)phys_ram_base))
> -#else
> -#define ARCH_PFN_OFFSET                (PAGE_OFFSET >> PAGE_SHIFT)
> -#endif /* CONFIG_MMU */
>
>  struct kernel_mapping {
>         unsigned long page_offset;
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index e79f15293492..e224ac66e635 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -12,7 +12,7 @@
>  #include <asm/pgtable-bits.h>
>
>  #ifndef CONFIG_MMU
> -#define KERNEL_LINK_ADDR       PAGE_OFFSET
> +#define KERNEL_LINK_ADDR       _AC(CONFIG_PAGE_OFFSET, UL)
>  #define KERN_VIRT_SIZE         (UL(-1))
>  #else
>
> --
> 2.45.1
>
>
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