On Thu, Aug 12, 2021 at 04:37:50PM -0700, Vineet Gupta wrote:
> ARCv2 MMU is software walked and Linux implements 2 levels of paging: pgd/pte.
> Forthcoming hw will have multiple levels, so this change preps mm code
> for same. It is also fun to try multi levels even on soft-walked code to
> ensure generic mm code is robust to handle.
>
> overview
> ________
>
> 2 levels {pgd, pte} : pmd is folded but pmd_* macros are valid and operate on pgd
> 3 levels {pgd, pmd, pte}:
> - pud is folded and pud_* macros point to pgd
> - pmd_* macros operate on actual pmd
>
> code changes
> ____________
>
> 1. #include <asm-generic/pgtable-nopud.h>
>
> 2. Define CONFIG_PGTABLE_LEVELS 3
>
> 3a. Define PMD_SHIFT, PMD_SIZE, PMD_MASK, pmd_t
> 3b. Define pmd_val() which actually deals with pmd
> (pmd_offset(), pmd_index() are provided by generic code)
> 3c. pmd_alloc_one()/pmd_free() also provided by generic code
> (pmd_populate/pmd_free already exist)
>
> 4. Define pud_none(), pud_bad() macros based on generic pud_val() which
> internally pertains to pgd now.
> 4b. define pud_populate() to just setup pgd
>
> Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxx>
> ---
...
> diff --git a/arch/arc/include/asm/pgtable-levels.h b/arch/arc/include/asm/pgtable-levels.h
> index 8ece75335bb5..1c2f022d4ad0 100644
> --- a/arch/arc/include/asm/pgtable-levels.h
> +++ b/arch/arc/include/asm/pgtable-levels.h
> @@ -10,6 +10,8 @@
> #ifndef _ASM_ARC_PGTABLE_LEVELS_H
> #define _ASM_ARC_PGTABLE_LEVELS_H
>
> +#if CONFIG_PGTABLE_LEVELS == 2
> +
> /*
> * 2 level paging setup for software walked MMUv3 (ARC700) and MMUv4 (HS)
> *
> @@ -37,16 +39,38 @@
> #define PGDIR_SHIFT 21
> #endif
>
> -#define PGDIR_SIZE BIT(PGDIR_SHIFT) /* vaddr span, not PDG sz */
> -#define PGDIR_MASK (~(PGDIR_SIZE - 1))
> +#else
Adding /* CONFIG_PGTABLE_LEVELS == 2 */ would make the whole thing a bit
more readable, I think.
> +
> +/*
> + * A default 3 level paging testing setup in software walked MMU
> + * MMUv4 (8K page): <4> : <7> : <8> : <13>
> + */
> +#define PGDIR_SHIFT 28
> +#if CONFIG_PGTABLE_LEVELS > 2
> +#define PMD_SHIFT 21
> +#endif
> +
> +#endif
and here as well.
> +#define PGDIR_SIZE BIT(PGDIR_SHIFT)
> +#define PGDIR_MASK (~(PGDIR_SIZE - 1))
> #define PTRS_PER_PGD BIT(32 - PGDIR_SHIFT)
>
> -#define PTRS_PER_PTE BIT(PGDIR_SHIFT - PAGE_SHIFT)
> +#if CONFIG_PGTABLE_LEVELS > 2
> +#define PMD_SIZE BIT(PMD_SHIFT)
> +#define PMD_MASK (~(PMD_SIZE - 1))
> +#define PTRS_PER_PMD BIT(PGDIR_SHIFT - PMD_SHIFT)
> +#endif
> +
> +#define PTRS_PER_PTE BIT(PMD_SHIFT - PAGE_SHIFT)
>
--
Sincerely yours,
Mike.
