On Tue, 2016-02-09 at 06:50 +0530, Aneesh Kumar K.V wrote:
>
> Also make sure we wait for irq disable section in other cpus to finish
> before flipping a huge pte entry with a regular pmd entry. Code paths
> like find_linux_pte_or_hugepte depend on irq disable to get
> a stable pte_t pointer. A parallel thp split need to make sure we
> don't convert a pmd pte to a regular pmd entry without waiting for the
> irq disable section to finish.
>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/include/asm/book3s/64/pgtable.h | 4 ++++
> arch/powerpc/mm/pgtable_64.c | 35
> +++++++++++++++++++++++++++-
> include/asm-generic/pgtable.h | 8 +++++++
> mm/huge_memory.c | 1 +
> 4 files changed, 47 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h
> b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 8d1c41d28318..ac07a30a7934 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -281,6 +281,10 @@ extern pgtable_t pgtable_trans_huge_withdraw(struct
> mm_struct *mm, pmd_t *pmdp);
> extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long
> address,
> pmd_t *pmdp);
>
> +#define __HAVE_ARCH_PMDP_HUGE_SPLIT_PREPARE
> +extern void pmdp_huge_split_prepare(struct vm_area_struct *vma,
> + unsigned long address, pmd_t *pmdp);
> +
> #define pmd_move_must_withdraw pmd_move_must_withdraw
> struct spinlock;
> static inline int pmd_move_must_withdraw(struct spinlock *new_pmd_ptl,
> diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
> index 3124a20d0fab..c8a00da39969 100644
> --- a/arch/powerpc/mm/pgtable_64.c
> +++ b/arch/powerpc/mm/pgtable_64.c
> @@ -646,6 +646,30 @@ pgtable_t pgtable_trans_huge_withdraw(struct mm_struct
> *mm, pmd_t *pmdp)
> return pgtable;
> }
>
> +void pmdp_huge_split_prepare(struct vm_area_struct *vma,
> + unsigned long address, pmd_t *pmdp)
> +{
> + VM_BUG_ON(address & ~HPAGE_PMD_MASK);
> +
> +#ifdef CONFIG_DEBUG_VM
> + BUG_ON(REGION_ID(address) != USER_REGION_ID);
> +#endif
> + /*
> + * We can't mark the pmd none here, because that will cause a race
> + * against exit_mmap. We need to continue mark pmd TRANS HUGE, while
> + * we spilt, but at the same time we wan't rest of the ppc64 code
> + * not to insert hash pte on this, because we will be modifying
> + * the deposited pgtable in the caller of this function. Hence
> + * clear the _PAGE_USER so that we move the fault handling to
> + * higher level function and that will serialize against ptl.
> + * We need to flush existing hash pte entries here even though,
> + * the translation is still valid, because we will withdraw
> + * pgtable_t after this.
> + */
> + pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_USER, 0);
Can this break any checks for _PAGE_USER? From other paths?
> +}
> +
> +
> /*
> * set a new huge pmd. We should not be called for updating
> * an existing pmd entry. That should go via pmd_hugepage_update.
> @@ -663,10 +687,19 @@ void set_pmd_at(struct mm_struct *mm, unsigned long
> addr,
> return set_pte_at(mm, addr, pmdp_ptep(pmdp), pmd_pte(pmd));
> }
>
> +/*
> + * We use this to invalidate a pmdp entry before switching from a
> + * hugepte to regular pmd entry.
> + */
> void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
> pmd_t *pmdp)
> {
> - pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_PRESENT, 0);
> + pmd_hugepage_update(vma->vm_mm, address, pmdp, ~0UL, 0);
> + /*
> + * This ensures that generic code that rely on IRQ disabling
> + * to prevent a parallel THP split work as expected.
> + */
> + kick_all_cpus_sync();
Seems expensive, anyway I think the right should do something like or a wrapper
for it
on_each_cpu_mask(mm_cpumask(vma->vm_mm), do_nothing, NULL, 1);
do_nothing is not exported, but that can be fixed :)
Balbir Singh
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