"Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> writes:
> Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>>
>> This patch fix the below crash
>>
>> NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
>> LR [c0000000000439ac] .hash_page+0x18c/0x5e0
>> ...
>> Call Trace:
>> [c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
>> [437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
>> [437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58
>>
>> On ppc64 we use the pgtable for storing the hpte slot information and
>> store address to the pgtable at a constant offset (PTRS_PER_PMD) from
>> pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
>> the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
>> from new pmd.
>>
>> We also want to move the withdraw and deposit before the set_pmd so
>> that, when page fault find the pmd as trans huge we can be sure that
>> pgtable can be located at the offset.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>> ---
>> Changes from V1:
>> * limit the withraw/deposit to only ppc64
>>
>> arch/Kconfig | 3 +++
>> arch/powerpc/platforms/Kconfig.cputype | 1 +
>> include/linux/huge_mm.h | 6 ++++++
>> mm/huge_memory.c | 21 ++++++++++++---------
>> 4 files changed, 22 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/Kconfig b/arch/Kconfig
>> index f1cf895c040f..3759e70a649d 100644
>> --- a/arch/Kconfig
>> +++ b/arch/Kconfig
>> @@ -371,6 +371,9 @@ config HAVE_IRQ_TIME_ACCOUNTING
>> config HAVE_ARCH_TRANSPARENT_HUGEPAGE
>> bool
>>
>> +config ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
>
> I don't like name of the option, but can't find any better... :(
>
>> + bool
>> +
>> config HAVE_ARCH_SOFT_DIRTY
>> bool
>>
>> diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
>> index bca2465a9c34..5f83b4334e5f 100644
>> --- a/arch/powerpc/platforms/Kconfig.cputype
>> +++ b/arch/powerpc/platforms/Kconfig.cputype
>> @@ -71,6 +71,7 @@ config PPC_BOOK3S_64
>> select PPC_FPU
>> select PPC_HAVE_PMU_SUPPORT
>> select SYS_SUPPORTS_HUGETLBFS
>> + select ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
>> select HAVE_ARCH_TRANSPARENT_HUGEPAGE if PPC_64K_PAGES
>>
>> config PPC_BOOK3E_64
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 91672e2deec3..836242a738a5 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -230,4 +230,10 @@ static inline int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_str
>>
>> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>>
>> +#ifdef CONFIG_ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW
>> +#define ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW 1
>> +#else
>> +#define ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW 0
>> +#endif
>> +
>
> Just use config option directly:
>
> if (new_ptl != old_ptl ||
> IS_ENABLED(CONFIG_ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW))
I didn't like that. I found the earlier one easier for reading.
If you and others strongly feel about this, I can redo the patch. Please let me know
> ...
>
>
> Otherwise, looks good:
>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
>
>> #endif /* _LINUX_HUGE_MM_H */
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 7de1bf85f683..32006b51d102 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -1505,19 +1505,22 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
>> spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
>> pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
>> VM_BUG_ON(!pmd_none(*new_pmd));
>> - set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
>> - if (new_ptl != old_ptl) {
>> + /*
>> + * Archs like ppc64 use pgtable to store per pmd
>> + * specific information. So when we switch the pmd,
>> + * we should also withdraw and deposit the pgtable
>> + *
>> + * With split pmd lock we also need to move preallocated
>> + * PTE page table if new_pmd is on different PMD page table.
>> + */
>> + if (new_ptl != old_ptl || ARCH_THP_MOVE_PMD_ALWAYS_WITHDRAW) {
>> pgtable_t pgtable;
>> -
>> - /*
>> - * Move preallocated PTE page table if new_pmd is on
>> - * different PMD page table.
>> - */
>> pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
>> pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
>> -
>> - spin_unlock(new_ptl);
>> }
>> + set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
>> + if (new_ptl != old_ptl)
>> + spin_unlock(new_ptl);
>> spin_unlock(old_ptl);
>> }
>> out:
>> --
>> 1.8.3.2
>
> --
> Kirill A. Shutemov
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