From a73fbd8f6269867e707000837f065ce553bca25b Mon Sep 17 00:00:00 2001 From: James Houghton Date: Thu, 5 Jan 2023 10:18:10 +0000 Subject: [PATCH] hugetlb: add hugetlb_alloc_pmd and hugetlb_alloc_pte These functions are used to allocate new PTEs below the hstate PTE. This will be used by hugetlb_walk_step, which implements stepping forwards in a HugeTLB high-granularity page table walk. The reasons that we don't use the standard pmd_alloc/pte_alloc* functions are: 1) This prevents us from accidentally overwriting swap entries or attempting to use swap entries as present non-leaf PTEs (see pmd_alloc(); we assume that !pte_none means pte_present and non-leaf). 2) Locking hugetlb PTEs can different than regular PTEs. (Although, as implemented right now, locking is the same.) 3) We can maintain compatibility with CONFIG_HIGHPTE. That is, HugeTLB HGM won't use HIGHPTE, but the kernel can still be built with it, and other mm code will use it. When GENERAL_HUGETLB supports P4D-based hugepages, we will need to implement hugetlb_pud_alloc to implement hugetlb_walk_step. Signed-off-by: James Houghton --- include/linux/hugetlb.h | 5 ++ mm/hugetlb.c | 114 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 119 insertions(+) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index bf441d8a1b5259..ad9d19f0d1b949 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -86,6 +86,11 @@ unsigned long hugetlb_pte_mask(const struct hugetlb_pte *hpte) bool hugetlb_pte_present_leaf(const struct hugetlb_pte *hpte, pte_t pte); +pmd_t *hugetlb_alloc_pmd(struct mm_struct *mm, struct hugetlb_pte *hpte, + unsigned long addr); +pte_t *hugetlb_alloc_pte(struct mm_struct *mm, struct hugetlb_pte *hpte, + unsigned long addr); + struct hugepage_subpool { spinlock_t lock; long count; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 2d83a2c359a26c..2160cbaf3311d1 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -480,6 +480,120 @@ static bool has_same_uncharge_info(struct file_region *rg, #endif } +/* + * hugetlb_alloc_pmd -- Allocate or find a PMD beneath a PUD-level hpte. + * + * This is meant to be used to implement hugetlb_walk_step when one must go to + * step down to a PMD. Different architectures may implement hugetlb_walk_step + * differently, but hugetlb_alloc_pmd and hugetlb_alloc_pte are architecture- + * independent. + * + * Returns: + * On success: the pointer to the PMD. This should be placed into a + * hugetlb_pte. @hpte is not changed. + * ERR_PTR(-EINVAL): hpte is not PUD-level + * ERR_PTR(-EEXIST): there is a non-leaf and non-empty PUD in @hpte + * ERR_PTR(-ENOMEM): could not allocate the new PMD + */ +pmd_t *hugetlb_alloc_pmd(struct mm_struct *mm, struct hugetlb_pte *hpte, + unsigned long addr) +{ + spinlock_t *ptl = hugetlb_pte_lockptr(hpte); + pmd_t *new; + pud_t *pudp; + pud_t pud; + + if (hpte->level != HUGETLB_LEVEL_PUD) + return ERR_PTR(-EINVAL); + + pudp = (pud_t *)hpte->ptep; +retry: + pud = READ_ONCE(*pudp); + if (likely(pud_present(pud))) + return unlikely(pud_leaf(pud)) + ? ERR_PTR(-EEXIST) + : pmd_offset(pudp, addr); + else if (!pud_none(pud)) + /* + * Not present and not none means that a swap entry lives here, + * and we can't get rid of it. + */ + return ERR_PTR(-EEXIST); + + new = pmd_alloc_one(mm, addr); + if (!new) + return ERR_PTR(-ENOMEM); + + spin_lock(ptl); + if (!pud_same(pud, *pudp)) { + spin_unlock(ptl); + pmd_free(mm, new); + goto retry; + } + + mm_inc_nr_pmds(mm); + smp_wmb(); /* See comment in pmd_install() */ + pud_populate(mm, pudp, new); + spin_unlock(ptl); + return pmd_offset(pudp, addr); +} + +/* + * hugetlb_alloc_pte -- Allocate a PTE beneath a pmd_none PMD-level hpte. + * + * See the comment above hugetlb_alloc_pmd. + */ +pte_t *hugetlb_alloc_pte(struct mm_struct *mm, struct hugetlb_pte *hpte, + unsigned long addr) +{ + spinlock_t *ptl = hugetlb_pte_lockptr(hpte); + pgtable_t new; + pmd_t *pmdp; + pmd_t pmd; + + if (hpte->level != HUGETLB_LEVEL_PMD) + return ERR_PTR(-EINVAL); + + pmdp = (pmd_t *)hpte->ptep; +retry: + pmd = READ_ONCE(*pmdp); + if (likely(pmd_present(pmd))) + return unlikely(pmd_leaf(pmd)) + ? ERR_PTR(-EEXIST) + : pte_offset_kernel(pmdp, addr); + else if (!pmd_none(pmd)) + /* + * Not present and not none means that a swap entry lives here, + * and we can't get rid of it. + */ + return ERR_PTR(-EEXIST); + + /* + * With CONFIG_HIGHPTE, calling `pte_alloc_one` directly may result + * in page tables being allocated in high memory, needing a kmap to + * access. Instead, we call __pte_alloc_one directly with + * GFP_PGTABLE_USER to prevent these PTEs being allocated in high + * memory. + */ + new = __pte_alloc_one(mm, GFP_PGTABLE_USER); + if (!new) + return ERR_PTR(-ENOMEM); + + spin_lock(ptl); + if (!pmd_same(pmd, *pmdp)) { + spin_unlock(ptl); + pgtable_pte_page_dtor(new); + __free_page(new); + goto retry; + } + + mm_inc_nr_ptes(mm); + smp_wmb(); /* See comment in pmd_install() */ + pmd_populate(mm, pmdp, new); + spin_unlock(ptl); + return pte_offset_kernel(pmdp, addr); +} + static void coalesce_file_region(struct resv_map *resv, struct file_region *rg) { struct file_region *nrg, *prg;