[RFC PATCH 04/12] riscv: Allow to dynamically define VA_BITS

[Anup Patel]

On Tue, Jan 5, 2021 at 1:33 AM Alexandre Ghiti <alex at ghiti.fr> wrote:
>
> With 4-level page table folding at runtime, we don't know at compile time
> the size of the virtual address space so we must set VA_BITS dynamically
> so that sparsemem reserves the right amount of memory for struct pages.
>
> Signed-off-by: Alexandre Ghiti <alex at ghiti.fr>
> ---
>  arch/riscv/Kconfig                 | 10 ----------
>  arch/riscv/include/asm/pgtable.h   | 11 +++++++++--
>  arch/riscv/include/asm/sparsemem.h |  6 +++++-
>  3 files changed, 14 insertions(+), 13 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 44377fd7860e..2979a44103be 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -122,16 +122,6 @@ config ZONE_DMA32
>         bool
>         default y if 64BIT
>
> -config VA_BITS
> -       int
> -       default 32 if 32BIT
> -       default 39 if 64BIT
> -
> -config PA_BITS
> -       int
> -       default 34 if 32BIT
> -       default 56 if 64BIT
> -
>  config PAGE_OFFSET
>         hex
>         default 0xC0000000 if 32BIT && MAXPHYSMEM_2GB
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 102b728ca146..c7973bfd65bc 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -43,8 +43,14 @@
>   * struct pages to map half the virtual address space. Then
>   * position vmemmap directly below the VMALLOC region.
>   */
> +#ifdef CONFIG_64BIT
> +#define VA_BITS                39
> +#else
> +#define VA_BITS                32
> +#endif
> +
>  #define VMEMMAP_SHIFT \
> -       (CONFIG_VA_BITS - PAGE_SHIFT - 1 + STRUCT_PAGE_MAX_SHIFT)
> +       (VA_BITS - PAGE_SHIFT - 1 + STRUCT_PAGE_MAX_SHIFT)
>  #define VMEMMAP_SIZE   BIT(VMEMMAP_SHIFT)
>  #define VMEMMAP_END    (VMALLOC_START - 1)
>  #define VMEMMAP_START  (VMALLOC_START - VMEMMAP_SIZE)
> @@ -83,6 +89,7 @@
>  #endif /* CONFIG_64BIT */
>
>  #ifdef CONFIG_MMU
> +
>  /* Number of entries in the page global directory */
>  #define PTRS_PER_PGD    (PAGE_SIZE / sizeof(pgd_t))
>  /* Number of entries in the page table */
> @@ -453,7 +460,7 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
>   * and give the kernel the other (upper) half.
>   */
>  #ifdef CONFIG_64BIT
> -#define KERN_VIRT_START        (-(BIT(CONFIG_VA_BITS)) + TASK_SIZE)
> +#define KERN_VIRT_START        (-(BIT(VA_BITS)) + TASK_SIZE)
>  #else
>  #define KERN_VIRT_START        FIXADDR_START
>  #endif
> diff --git a/arch/riscv/include/asm/sparsemem.h b/arch/riscv/include/asm/sparsemem.h
> index 45a7018a8118..63acaecc3374 100644
> --- a/arch/riscv/include/asm/sparsemem.h
> +++ b/arch/riscv/include/asm/sparsemem.h
> @@ -4,7 +4,11 @@
>  #define _ASM_RISCV_SPARSEMEM_H
>
>  #ifdef CONFIG_SPARSEMEM
> -#define MAX_PHYSMEM_BITS       CONFIG_PA_BITS
> +#ifdef CONFIG_64BIT
> +#define MAX_PHYSMEM_BITS       56
> +#else
> +#define MAX_PHYSMEM_BITS       34
> +#endif /* CONFIG_64BIT */
>  #define SECTION_SIZE_BITS      27
>  #endif /* CONFIG_SPARSEMEM */
>
> --
> 2.20.1
>

Looks good to me.

Reviewed-by: Anup Patel <anup at brainfault.org>

Regards,
Anup