linux-kernel - Re: [PATCH] RISC-V: redefine PTRS_PER_PGD/PTRS_PER_PMD/PTRS_PER

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Message-ID: <CAAhSdy1ra-khBQU2s14StbiojFMk4tokGqAbp-u3j51bksbjQA@mail.gmail.com>
Date:   Thu, 18 Apr 2019 11:43:27 +0530
From:   Anup Patel <anup@...infault.org>
To:     damon <liush.damon@...il.com>
Cc:     Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup.patel@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>, sorear2@...il.com,
        linux-riscv@...ts.infradead.org,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RISC-V: redefine PTRS_PER_PGD/PTRS_PER_PMD/PTRS_PER_PTE

On Thu, Apr 18, 2019 at 6:26 AM damon <liush.damon@...il.com> wrote:
>
> Use the number of addresses to define the relevant macros.
>
> Signed-off-by: damon <liush.damon@...il.com>
> ---
>  arch/riscv/include/asm/pgtable-32.h | 2 ++
>  arch/riscv/include/asm/pgtable-64.h | 3 ++-
>  arch/riscv/include/asm/pgtable.h    | 4 ++--
>  3 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/include/asm/pgtable-32.h b/arch/riscv/include/asm/pgtable-32.h
> index d61974b7..93607f6 100644
> --- a/arch/riscv/include/asm/pgtable-32.h
> +++ b/arch/riscv/include/asm/pgtable-32.h
> @@ -17,8 +17,10 @@
>  #include <asm-generic/pgtable-nopmd.h>
>  #include <linux/const.h>
>
> +#define MAX_USER_VA_BITS       32
>  /* Size of region mapped by a page global directory */
>  #define PGDIR_SHIFT     22
> +#define PMD_SHIFT       PGDIR_SHIFT

We don't have PMD in RV32. We have only two level page table
for RV32 so defining PMD_SHIFT is misleading and in-correct.

I suggest you drop PMD_SHIFT here instead look at below
suggestion for defining PTRS_PER_PTE  in asm/pgtable.h

>  #define PGDIR_SIZE      (_AC(1, UL) << PGDIR_SHIFT)
>  #define PGDIR_MASK      (~(PGDIR_SIZE - 1))
>
> diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
> index 7aa0ea9..a56d4d0 100644
> --- a/arch/riscv/include/asm/pgtable-64.h
> +++ b/arch/riscv/include/asm/pgtable-64.h
> @@ -16,6 +16,7 @@
>
>  #include <linux/const.h>
>
> +#define MAX_USER_VA_BITS       39
>  #define PGDIR_SHIFT     30
>  /* Size of region mapped by a page global directory */
>  #define PGDIR_SIZE      (_AC(1, UL) << PGDIR_SHIFT)
> @@ -34,7 +35,7 @@
>  #define pmd_val(x)      ((x).pmd)
>  #define __pmd(x)        ((pmd_t) { (x) })
>
> -#define PTRS_PER_PMD    (PAGE_SIZE / sizeof(pmd_t))
> +#define PTRS_PER_PMD    (1 << (PGDIR_SHIFT - PMD_SHIFT))
>
>  static inline int pud_present(pud_t pud)
>  {
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 1141364..d9cb3c8 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -33,9 +33,9 @@
>  #endif /* CONFIG_64BIT */
>
>  /* Number of entries in the page global directory */
> -#define PTRS_PER_PGD    (PAGE_SIZE / sizeof(pgd_t))
> +#define PTRS_PER_PGD (1 << (MAX_USER_VA_BITS - PGDIR_SHIFT))
>  /* Number of entries in the page table */
> -#define PTRS_PER_PTE    (PAGE_SIZE / sizeof(pte_t))
> +#define PTRS_PER_PTE   (1 << (PMD_SHIFT - PAGE_SHIFT))

Instead of defining PTRS_PER_PTD using PMD_SHIFT for both RV32
and RV64, do the following:

#ifdef __PAGETABLE_PMD_FOLDED
#define PTRS_PER_PTE   (1 << (PGDIR_SHIFT - PAGE_SHIFT))
#else
#define PTRS_PER_PTE   (1 << (PMD_SHIFT - PAGE_SHIFT))
#endif

>
>  /* Number of PGD entries that a user-mode program can use */
>  #define USER_PTRS_PER_PGD   (TASK_SIZE / PGDIR_SIZE)
> --
> 1.9.1
>

Regards,
Anup