Re: [PATCH v3 9/9] riscv: mm: Add support for ZONE_DEVICE

[Alexandre Ghiti <alexghiti@rivosinc.com>]

On Tue, May 21, 2024 at 1:49 PM Björn Töpel <bjorn@kernel.org> wrote:
>
> From: Björn Töpel <bjorn@rivosinc.com>
>
> ZONE_DEVICE pages need DEVMAP PTEs support to function
> (ARCH_HAS_PTE_DEVMAP). Claim another RSW (reserved for software) bit
> in the PTE for DEVMAP mark, add the corresponding helpers, and enable
> ARCH_HAS_PTE_DEVMAP for riscv64.
>
> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
> ---
>  arch/riscv/Kconfig                    |  1 +
>  arch/riscv/include/asm/pgtable-64.h   | 20 ++++++++++++++++++++
>  arch/riscv/include/asm/pgtable-bits.h |  1 +
>  arch/riscv/include/asm/pgtable.h      | 17 +++++++++++++++++
>  4 files changed, 39 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 2724dc2af29f..0b74698c63c7 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -36,6 +36,7 @@ config RISCV
>         select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>         select ARCH_HAS_PMEM_API
>         select ARCH_HAS_PREPARE_SYNC_CORE_CMD
> +       select ARCH_HAS_PTE_DEVMAP if 64BIT && MMU
>         select ARCH_HAS_PTE_SPECIAL
>         select ARCH_HAS_SET_DIRECT_MAP if MMU
>         select ARCH_HAS_SET_MEMORY if MMU
> diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
> index 221a5c1ee287..c67a9bbfd010 100644
> --- a/arch/riscv/include/asm/pgtable-64.h
> +++ b/arch/riscv/include/asm/pgtable-64.h
> @@ -400,4 +400,24 @@ static inline struct page *pgd_page(pgd_t pgd)
>  #define p4d_offset p4d_offset
>  p4d_t *p4d_offset(pgd_t *pgd, unsigned long address);
>
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static inline int pte_devmap(pte_t pte);
> +static inline pte_t pmd_pte(pmd_t pmd);
> +
> +static inline int pmd_devmap(pmd_t pmd)
> +{
> +       return pte_devmap(pmd_pte(pmd));
> +}
> +
> +static inline int pud_devmap(pud_t pud)
> +{
> +       return 0;
> +}
> +
> +static inline int pgd_devmap(pgd_t pgd)
> +{
> +       return 0;
> +}
> +#endif
> +
>  #endif /* _ASM_RISCV_PGTABLE_64_H */
> diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
> index 179bd4afece4..a8f5205cea54 100644
> --- a/arch/riscv/include/asm/pgtable-bits.h
> +++ b/arch/riscv/include/asm/pgtable-bits.h
> @@ -19,6 +19,7 @@
>  #define _PAGE_SOFT      (3 << 8)    /* Reserved for software */
>
>  #define _PAGE_SPECIAL   (1 << 8)    /* RSW: 0x1 */
> +#define _PAGE_DEVMAP    (1 << 9)    /* RSW, devmap */
>  #define _PAGE_TABLE     _PAGE_PRESENT
>
>  /*
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 7933f493db71..02fadc276064 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -387,6 +387,13 @@ static inline int pte_special(pte_t pte)
>         return pte_val(pte) & _PAGE_SPECIAL;
>  }
>
> +#ifdef CONFIG_ARCH_HAS_PTE_DEVMAP
> +static inline int pte_devmap(pte_t pte)
> +{
> +       return pte_val(pte) & _PAGE_DEVMAP;
> +}
> +#endif

Not sure you need the #ifdef here.

> +
>  /* static inline pte_t pte_rdprotect(pte_t pte) */
>
>  static inline pte_t pte_wrprotect(pte_t pte)
> @@ -428,6 +435,11 @@ static inline pte_t pte_mkspecial(pte_t pte)
>         return __pte(pte_val(pte) | _PAGE_SPECIAL);
>  }
>
> +static inline pte_t pte_mkdevmap(pte_t pte)
> +{
> +       return __pte(pte_val(pte) | _PAGE_DEVMAP);
> +}
> +
>  static inline pte_t pte_mkhuge(pte_t pte)
>  {
>         return pte;
> @@ -711,6 +723,11 @@ static inline pmd_t pmd_mkdirty(pmd_t pmd)
>         return pte_pmd(pte_mkdirty(pmd_pte(pmd)));
>  }
>
> +static inline pmd_t pmd_mkdevmap(pmd_t pmd)
> +{
> +       return pte_pmd(pte_mkdevmap(pmd_pte(pmd)));
> +}
> +
>  static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
>                                 pmd_t *pmdp, pmd_t pmd)
>  {
> --
> 2.40.1
>

Otherwise, you can add:

Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Thanks,

Alex