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

["Björn Töpel" <bjorn@kernel.org>]

Alexandre Ghiti <alexghiti@rivosinc.com> writes:

> 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.

W/o it 32b builds break (!defined(CONFIG_ARCH_HAS_PTE_DEVMAP) will have
a default implementation).. Maybe it's cleaner just to use that instead?

>> +
>>  /* 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>

Thank you!


Björn