Re: [RFC PATCH 2/7] riscv: Allow to dynamically define VA_BITS

[Palmer Dabbelt]

On Sun, 22 Mar 2020 04:00:23 PDT (-0700), alex@xxxxxxxx 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@xxxxxxxx>
> ---
>  arch/riscv/Kconfig                 | 10 ----------
>  arch/riscv/include/asm/pgtable.h   | 10 +++++++++-
>  arch/riscv/include/asm/sparsemem.h |  2 +-
>  3 files changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index f5f3d474504d..8e4b1cbcf2c2 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -99,16 +99,6 @@ 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 185ffe3723ec..dce401eed1d3 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -26,6 +26,14 @@
>  #endif /* CONFIG_64BIT */
>
>  #ifdef CONFIG_MMU
> +#ifdef CONFIG_64BIT
> +#define VA_BITS		39
> +#define PA_BITS		56
> +#else
> +#define VA_BITS		32
> +#define PA_BITS		34

We've moved to 32-bit physical addresses on rv32 in Linux.  The mismatch was
causing too many issues in generic code.

> +#endif
> +
>  /* Number of entries in the page global directory */
>  #define PTRS_PER_PGD    (PAGE_SIZE / sizeof(pgd_t))
>  /* Number of entries in the page table */
> @@ -108,7 +116,7 @@ extern pgd_t swapper_pg_dir[];
>   * position vmemmap directly below the VMALLOC region.
>   */
>  #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)
> diff --git a/arch/riscv/include/asm/sparsemem.h b/arch/riscv/include/asm/sparsemem.h
> index 45a7018a8118..f08d72155bc8 100644
> --- a/arch/riscv/include/asm/sparsemem.h
> +++ b/arch/riscv/include/asm/sparsemem.h
> @@ -4,7 +4,7 @@
>  #define _ASM_RISCV_SPARSEMEM_H
>
>  #ifdef CONFIG_SPARSEMEM
> -#define MAX_PHYSMEM_BITS	CONFIG_PA_BITS
> +#define MAX_PHYSMEM_BITS	PA_BITS
>  #define SECTION_SIZE_BITS	27
>  #endif /* CONFIG_SPARSEMEM */

Aside from the 32-bit PA issue:

Reviewed-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>