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SubjectRe: [PATCH v9 11/21] mm: pagewalk: Add p4d_entry() and pgd_entry()
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On 07/22/2019 09:12 PM, Steven Price wrote:
> pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410
> ("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were
> no users. We're about to add users so reintroduce them, along with
> p4d_entry() as we now have 5 levels of tables.
>
> Note that commit a00cc7d9dd93d66a ("mm, x86: add support for
> PUD-sized transparent hugepages") already re-added pud_entry() but with
> different semantics to the other callbacks. Since there have never
> been upstream users of this, revert the semantics back to match the
> other callbacks. This means pud_entry() is called for all entries, not
> just transparent huge pages.
>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> include/linux/mm.h | 15 +++++++++------
> mm/pagewalk.c | 27 ++++++++++++++++-----------
> 2 files changed, 25 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0334ca97c584..b22799129128 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1432,15 +1432,14 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
>
> /**
> * mm_walk - callbacks for walk_page_range
> - * @pud_entry: if set, called for each non-empty PUD (2nd-level) entry
> - * this handler should only handle pud_trans_huge() puds.
> - * the pmd_entry or pte_entry callbacks will be used for
> - * regular PUDs.
> - * @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry
> + * @pgd_entry: if set, called for each non-empty PGD (top-level) entry
> + * @p4d_entry: if set, called for each non-empty P4D entry
> + * @pud_entry: if set, called for each non-empty PUD entry
> + * @pmd_entry: if set, called for each non-empty PMD entry
> * this handler is required to be able to handle
> * pmd_trans_huge() pmds. They may simply choose to
> * split_huge_page() instead of handling it explicitly.
> - * @pte_entry: if set, called for each non-empty PTE (4th-level) entry
> + * @pte_entry: if set, called for each non-empty PTE (lowest-level) entry
> * @pte_hole: if set, called for each hole at all levels
> * @hugetlb_entry: if set, called for each hugetlb entry
> * @test_walk: caller specific callback function to determine whether
> @@ -1455,6 +1454,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
> * (see the comment on walk_page_range() for more details)
> */
> struct mm_walk {
> + int (*pgd_entry)(pgd_t *pgd, unsigned long addr,
> + unsigned long next, struct mm_walk *walk);
> + int (*p4d_entry)(p4d_t *p4d, unsigned long addr,
> + unsigned long next, struct mm_walk *walk);
> int (*pud_entry)(pud_t *pud, unsigned long addr,
> unsigned long next, struct mm_walk *walk);
> int (*pmd_entry)(pmd_t *pmd, unsigned long addr,
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index c3084ff2569d..98373a9f88b8 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -90,15 +90,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
> }
>
> if (walk->pud_entry) {
> - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma);
> -
> - if (ptl) {
> - err = walk->pud_entry(pud, addr, next, walk);
> - spin_unlock(ptl);
> - if (err)
> - break;
> - continue;
> - }
> + err = walk->pud_entry(pud, addr, next, walk);
> + if (err)
> + break;

But will not this still encounter possible THP entries when walking user
page tables (valid walk->vma) in which case still needs to get a lock.
OR will the callback take care of it ?

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