Re: [PATCH 4/6] powerpc/mm: Add devmap support for ppc64

["Oliver O'Halloran" <oohall@gmail.com>]

On Tue, May 23, 2017 at 8:40 PM, Balbir Singh <bsingharora@gmail.com> wrote:
> On Tue, May 23, 2017 at 2:05 PM, Oliver O'Halloran <oohall@gmail.com> wrote:
>> Add support for the devmap bit on PTEs and PMDs for PPC64 Book3S.  This
>> is used to differentiate device backed memory from transparent huge
>> pages since they are handled in more or less the same manner by the core
>> mm code.
>>
>> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>> Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
>> ---
>> v1 -> v2: Properly differentiate THP and PMD Devmap entries. The
>> mm core assumes that pmd_trans_huge() and pmd_devmap() are mutually
>> exclusive and v1 had pmd_trans_huge() being true on a devmap pmd.
>>
>> Aneesh, this has been fleshed out substantially since v1. Can you
>> re-review it? Also no explicit gup support is required in this patch
>> since devmap support was added generic GUP as a part of making x86 use
>> the generic version.
>> ---
>>  arch/powerpc/include/asm/book3s/64/hash-64k.h |  2 +-
>>  arch/powerpc/include/asm/book3s/64/pgtable.h  | 37 ++++++++++++++++++++++++++-
>>  arch/powerpc/include/asm/book3s/64/radix.h    |  2 +-
>>  arch/powerpc/mm/hugetlbpage.c                 |  2 +-
>>  arch/powerpc/mm/pgtable-book3s64.c            |  4 +--
>>  arch/powerpc/mm/pgtable-hash64.c              |  4 ++-
>>  arch/powerpc/mm/pgtable-radix.c               |  3 ++-
>>  arch/powerpc/mm/pgtable_64.c                  |  2 +-
>>  8 files changed, 47 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/book3s/64/hash-64k.h b/arch/powerpc/include/asm/book3s/64/hash-64k.h
>> index 9732837aaae8..eaaf613c5347 100644
>> --- a/arch/powerpc/include/asm/book3s/64/hash-64k.h
>> +++ b/arch/powerpc/include/asm/book3s/64/hash-64k.h
>> @@ -180,7 +180,7 @@ static inline void mark_hpte_slot_valid(unsigned char *hpte_slot_array,
>>   */
>>  static inline int hash__pmd_trans_huge(pmd_t pmd)
>>  {
>> -       return !!((pmd_val(pmd) & (_PAGE_PTE | H_PAGE_THP_HUGE)) ==
>> +       return !!((pmd_val(pmd) & (_PAGE_PTE | H_PAGE_THP_HUGE | _PAGE_DEVMAP)) ==
>>                   (_PAGE_PTE | H_PAGE_THP_HUGE));
>>  }
>
> Like Aneesh suggested, I think we can probably skip this check here
>
>>
>> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
>> index 85bc9875c3be..24634e92dd0b 100644
>> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
>> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
>> @@ -79,6 +79,9 @@
>>
>>  #define _PAGE_SOFT_DIRTY       _RPAGE_SW3 /* software: software dirty tracking */
>>  #define _PAGE_SPECIAL          _RPAGE_SW2 /* software: special page */
>> +#define _PAGE_DEVMAP           _RPAGE_SW1
>> +#define __HAVE_ARCH_PTE_DEVMAP
>> +
>>  /*
>>   * Drivers request for cache inhibited pte mapping using _PAGE_NO_CACHE
>>   * Instead of fixing all of them, add an alternate define which
>> @@ -599,6 +602,16 @@ static inline pte_t pte_mkhuge(pte_t pte)
>>         return pte;
>>  }
>>
>> +static inline pte_t pte_mkdevmap(pte_t pte)
>> +{
>> +       return __pte(pte_val(pte) | _PAGE_SPECIAL|_PAGE_DEVMAP);
>> +}
>> +
>> +static inline int pte_devmap(pte_t pte)
>> +{
>> +       return !!(pte_raw(pte) & cpu_to_be64(_PAGE_DEVMAP));
>> +}
>> +
>>  static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>>  {
>>         /* FIXME!! check whether this need to be a conditional */
>> @@ -963,6 +976,9 @@ static inline pte_t *pmdp_ptep(pmd_t *pmd)
>>  #define pmd_mk_savedwrite(pmd) pte_pmd(pte_mk_savedwrite(pmd_pte(pmd)))
>>  #define pmd_clear_savedwrite(pmd)      pte_pmd(pte_clear_savedwrite(pmd_pte(pmd)))
>>
>> +#define pud_pfn(...) (0)
>> +#define pgd_pfn(...) (0)
>> +
>
> Don't get these bits.. why are they zero?

I think that was just hacking stuff until it worked. pud_pfn() needs
to exist for the kernel to build when __HAVE_ARCH_PTE_DEVMAP is set,
but we don't need it to do anything (yet) since pud_pfn() is only used
for handing devmap PUD faults. We currently support those so we will
never hit that code path. pgd_pfn() can die though.

>>  #ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
>>  #define pmd_soft_dirty(pmd)    pte_soft_dirty(pmd_pte(pmd))
>>  #define pmd_mksoft_dirty(pmd)  pte_pmd(pte_mksoft_dirty(pmd_pte(pmd)))
>> @@ -1137,7 +1153,6 @@ static inline int pmd_move_must_withdraw(struct spinlock *new_pmd_ptl,
>>         return true;
>>  }
>>
>> -
>>  #define arch_needs_pgtable_deposit arch_needs_pgtable_deposit
>>  static inline bool arch_needs_pgtable_deposit(void)
>>  {
>> @@ -1146,6 +1161,26 @@ static inline bool arch_needs_pgtable_deposit(void)
>>         return true;
>>  }
>>
>> +static inline pmd_t pmd_mkdevmap(pmd_t pmd)
>> +{
>> +       return pte_pmd(pte_mkdevmap(pmd_pte(pmd)));
>> +}
>> +
>> +static inline int pmd_devmap(pmd_t pmd)
>> +{
>> +       return pte_devmap(pmd_pte(pmd));
>> +}
>
> This should be defined only if #ifdef __HAVE_ARCH_PTE_DEVMAP

ok

>
> The rest looks OK
>
> Balbir Singh.