On 2022/7/4 9:33, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
>
> follow_pud_mask() does not support non-present pud entry now. As long as
> I tested on x86_64 server, follow_pud_mask() still simply returns
> no_page_table() for non-present_pud_entry() due to pud_bad(), so no severe
> user-visible effect should happen. But generally we should call
> follow_huge_pud() for non-present pud entry for 1GB hugetlb page.
>
> Update pud_huge() and follow_huge_pud() to handle non-present pud entries.
> The changes are similar to previous works for pud entries commit e66f17ff7177
> ("mm/hugetlb: take page table lock in follow_huge_pmd()") and commit
> cbef8478bee5 ("mm/hugetlb: pmd_huge() returns true for non-present hugepage").
>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> ---
> v2 -> v3:
> - fixed typos in subject and description,
> - added comment on pud_huge(),
> - added comment about fallback for hwpoisoned entry,
> - updated initial check about FOLL_{PIN,GET} flags.
> ---
> arch/x86/mm/hugetlbpage.c | 8 +++++++-
> mm/hugetlb.c | 32 ++++++++++++++++++++++++++++++--
> 2 files changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
> index 509408da0da1..6b3033845c6d 100644
> --- a/arch/x86/mm/hugetlbpage.c
> +++ b/arch/x86/mm/hugetlbpage.c
> @@ -30,9 +30,15 @@ int pmd_huge(pmd_t pmd)
> (pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
> }
>
> +/*
> + * pud_huge() returns 1 if @pud is hugetlb related entry, that is normal
> + * hugetlb entry or non-present (migration or hwpoisoned) hugetlb entry.
> + * Otherwise, returns 0.
> + */
> int pud_huge(pud_t pud)
> {
> - return !!(pud_val(pud) & _PAGE_PSE);
> + return !pud_none(pud) &&
> + (pud_val(pud) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
> }
Question: Is aarch64 supported too? It seems aarch64 version of pud_huge matches
the requirement naturally for me.
Anyway, this patch looks good to me.
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Thanks.
>
> #ifdef CONFIG_HUGETLB_PAGE
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ad621688370b..66bb39e0fce8 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6994,10 +6994,38 @@ struct page * __weak
> follow_huge_pud(struct mm_struct *mm, unsigned long address,
> pud_t *pud, int flags)
> {
> - if (flags & (FOLL_GET | FOLL_PIN))
> + struct page *page = NULL;
> + spinlock_t *ptl;
> + pte_t pte;
> +
> + if (WARN_ON_ONCE(flags & FOLL_PIN))
> return NULL;
>
> - return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
> +retry:
> + ptl = huge_pte_lock(hstate_sizelog(PUD_SHIFT), mm, (pte_t *)pud);
> + if (!pud_huge(*pud))
> + goto out;
> + pte = huge_ptep_get((pte_t *)pud);
> + if (pte_present(pte)) {
> + page = pud_page(*pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
> + if (WARN_ON_ONCE(!try_grab_page(page, flags))) {
> + page = NULL;
> + goto out;
> + }
> + } else {
> + if (is_hugetlb_entry_migration(pte)) {
> + spin_unlock(ptl);
> + __migration_entry_wait(mm, (pte_t *)pud, ptl);
> + goto retry;
> + }
> + /*
> + * hwpoisoned entry is treated as no_page_table in
> + * follow_page_mask().
> + */
> + }
> +out:
> + spin_unlock(ptl);
> + return page;
> }
>
> struct page * __weak
>
