On 10/21/22 16:36, James Houghton wrote:
> hugetlb_hgm_walk implements high-granularity page table walks for
> HugeTLB. It is safe to call on non-HGM enabled VMAs; it will return
> immediately.
>
> hugetlb_walk_step implements how we step forwards in the walk. For
> architectures that don't use GENERAL_HUGETLB, they will need to provide
> their own implementation.
>
> Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
> ---
> include/linux/hugetlb.h | 13 +++++
> mm/hugetlb.c | 125 ++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 138 insertions(+)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 003255b0e40f..4b1548adecde 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -276,6 +276,10 @@ u32 hugetlb_fault_mutex_hash(struct address_space *mapping, pgoff_t idx);
> pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
> unsigned long addr, pud_t *pud);
>
> +int hugetlb_hgm_walk(struct mm_struct *mm, struct vm_area_struct *vma,
> + struct hugetlb_pte *hpte, unsigned long addr,
> + unsigned long sz, bool stop_at_none);
> +
> struct address_space *hugetlb_page_mapping_lock_write(struct page *hpage);
>
> extern int sysctl_hugetlb_shm_group;
> @@ -288,6 +292,8 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
> pte_t *huge_pte_offset(struct mm_struct *mm,
> unsigned long addr, unsigned long sz);
> unsigned long hugetlb_mask_last_page(struct hstate *h);
> +int hugetlb_walk_step(struct mm_struct *mm, struct hugetlb_pte *hpte,
> + unsigned long addr, unsigned long sz);
> int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
> unsigned long addr, pte_t *ptep);
> void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
> @@ -1066,6 +1072,8 @@ void hugetlb_register_node(struct node *node);
> void hugetlb_unregister_node(struct node *node);
> #endif
>
> +enum hugetlb_level hpage_size_to_level(unsigned long sz);
> +
> #else /* CONFIG_HUGETLB_PAGE */
> struct hstate {};
>
> @@ -1253,6 +1261,11 @@ static inline void hugetlb_register_node(struct node *node)
> static inline void hugetlb_unregister_node(struct node *node)
> {
> }
> +
> +static inline enum hugetlb_level hpage_size_to_level(unsigned long sz)
> +{
> + return HUGETLB_LEVEL_PTE;
> +}
> #endif /* CONFIG_HUGETLB_PAGE */
>
> #ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e3733388adee..90db59632559 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -95,6 +95,29 @@ static void hugetlb_vma_data_free(struct vm_area_struct *vma);
> static int hugetlb_vma_data_alloc(struct vm_area_struct *vma);
> static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma);
>
> +/*
> + * hpage_size_to_level() - convert @sz to the corresponding page table level
> + *
> + * @sz must be less than or equal to a valid hugepage size.
> + */
> +enum hugetlb_level hpage_size_to_level(unsigned long sz)
> +{
> + /*
> + * We order the conditionals from smallest to largest to pick the
> + * smallest level when multiple levels have the same size (i.e.,
> + * when levels are folded).
> + */
> + if (sz < PMD_SIZE)
> + return HUGETLB_LEVEL_PTE;
> + if (sz < PUD_SIZE)
> + return HUGETLB_LEVEL_PMD;
> + if (sz < P4D_SIZE)
> + return HUGETLB_LEVEL_PUD;
> + if (sz < PGDIR_SIZE)
> + return HUGETLB_LEVEL_P4D;
> + return HUGETLB_LEVEL_PGD;
> +}
> +
> static inline bool subpool_is_free(struct hugepage_subpool *spool)
> {
> if (spool->count)
> @@ -7321,6 +7344,70 @@ bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr)
> }
> #endif /* CONFIG_ARCH_WANT_HUGE_PMD_SHARE */
>
> +/* hugetlb_hgm_walk - walks a high-granularity HugeTLB page table to resolve
> + * the page table entry for @addr.
> + *
> + * @hpte must always be pointing at an hstate-level PTE (or deeper).
> + *
> + * This function will never walk further if it encounters a PTE of a size
> + * less than or equal to @sz.
> + *
> + * @stop_at_none determines what we do when we encounter an empty PTE. If true,
> + * we return that PTE. If false and @sz is less than the current PTE's size,
> + * we make that PTE point to the next level down, going until @sz is the same
> + * as our current PTE.
I was a bit confused about 'we return that PTE' when the function is of type
int. TBH, I am not a fan of the current scheme of passing in *hpte and having
the hpte modified by the function.
> + *
> + * If @stop_at_none is true and @sz is PAGE_SIZE, this function will always
> + * succeed, but that does not guarantee that hugetlb_pte_size(hpte) is @sz.
> + *
> + * Return:
> + * -ENOMEM if we couldn't allocate new PTEs.
> + * -EEXIST if the caller wanted to walk further than a migration PTE,
> + * poison PTE, or a PTE marker. The caller needs to manually deal
> + * with this scenario.
> + * -EINVAL if called with invalid arguments (@sz invalid, @hpte not
> + * initialized).
> + * 0 otherwise.
> + *
> + * Even if this function fails, @hpte is guaranteed to always remain
> + * valid.
> + */
> +int hugetlb_hgm_walk(struct mm_struct *mm, struct vm_area_struct *vma,
> + struct hugetlb_pte *hpte, unsigned long addr,
> + unsigned long sz, bool stop_at_none)
Since we are potentially populating lower level page tables, we may want a
different function name. It may just be me, but I think of walk as a read
only operation. I would suggest putting populate in the name, but as Peter
pointed out elsewhere, that has other implications. Sorry, I can not think
of something better right now.
--
Mike Kravetz
> +{
> + int ret = 0;
> + pte_t pte;
> +
> + if (WARN_ON_ONCE(sz < PAGE_SIZE))
> + return -EINVAL;
> +
> + if (!hugetlb_hgm_enabled(vma)) {
> + if (stop_at_none)
> + return 0;
> + return sz == huge_page_size(hstate_vma(vma)) ? 0 : -EINVAL;
> + }
> +
> + hugetlb_vma_assert_locked(vma);
> +
> + if (WARN_ON_ONCE(!hpte->ptep))
> + return -EINVAL;
> +
> + while (hugetlb_pte_size(hpte) > sz && !ret) {
> + pte = huge_ptep_get(hpte->ptep);
> + if (!pte_present(pte)) {
> + if (stop_at_none)
> + return 0;
> + if (unlikely(!huge_pte_none(pte)))
> + return -EEXIST;
> + } else if (hugetlb_pte_present_leaf(hpte, pte))
> + return 0;
> + ret = hugetlb_walk_step(mm, hpte, addr, sz);
> + }
> +
> + return ret;
> +}
> +
> #ifdef CONFIG_ARCH_WANT_GENERAL_HUGETLB
> pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
> unsigned long addr, unsigned long sz)
> @@ -7388,6 +7475,44 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
> return (pte_t *)pmd;
> }
>
> +/*
> + * hugetlb_walk_step() - Walk the page table one step to resolve the page
> + * (hugepage or subpage) entry at address @addr.
> + *
> + * @sz always points at the final target PTE size (e.g. PAGE_SIZE for the
> + * lowest level PTE).
> + *
> + * @hpte will always remain valid, even if this function fails.
> + */
> +int hugetlb_walk_step(struct mm_struct *mm, struct hugetlb_pte *hpte,
> + unsigned long addr, unsigned long sz)
> +{
> + pte_t *ptep;
> + spinlock_t *ptl;
> +
> + switch (hpte->level) {
> + case HUGETLB_LEVEL_PUD:
> + ptep = (pte_t *)hugetlb_pmd_alloc(mm, hpte, addr);
> + if (IS_ERR(ptep))
> + return PTR_ERR(ptep);
> + hugetlb_pte_populate(hpte, ptep, PMD_SHIFT, HUGETLB_LEVEL_PMD);
> + break;
> + case HUGETLB_LEVEL_PMD:
> + ptep = hugetlb_pte_alloc(mm, hpte, addr);
> + if (IS_ERR(ptep))
> + return PTR_ERR(ptep);
> + ptl = pte_lockptr(mm, (pmd_t *)hpte->ptep);
> + hugetlb_pte_populate(hpte, ptep, PAGE_SHIFT, HUGETLB_LEVEL_PTE);
> + hpte->ptl = ptl;
> + break;
> + default:
> + WARN_ONCE(1, "%s: got invalid level: %d (shift: %d)\n",
> + __func__, hpte->level, hpte->shift);
> + return -EINVAL;
> + }
> + return 0;
> +}
> +
> /*
> * Return a mask that can be used to update an address to the last huge
> * page in a page table page mapping size. Used to skip non-present
> --
> 2.38.0.135.g90850a2211-goog
>
