1 // SPDX-License-Identifier: GPL-2.0 2 3 /* 4 * Handling Page Tables through page fragments 5 * 6 */ 7 8 #include <linux/kernel.h> 9 #include <linux/gfp.h> 10 #include <linux/mm.h> 11 #include <linux/percpu.h> 12 #include <linux/hardirq.h> 13 #include <linux/hugetlb.h> 14 #include <asm/pgalloc.h> 15 #include <asm/tlbflush.h> 16 #include <asm/tlb.h> 17 18 void pte_frag_destroy(void *pte_frag) 19 { 20 int count; 21 struct ptdesc *ptdesc; 22 23 ptdesc = virt_to_ptdesc(pte_frag); 24 /* drop all the pending references */ 25 count = ((unsigned long)pte_frag & ~PAGE_MASK) >> PTE_FRAG_SIZE_SHIFT; 26 /* We allow PTE_FRAG_NR fragments from a PTE page */ 27 if (atomic_sub_and_test(PTE_FRAG_NR - count, &ptdesc->pt_frag_refcount)) { 28 pagetable_dtor(ptdesc); 29 pagetable_free(ptdesc); 30 } 31 } 32 33 static pte_t *get_pte_from_cache(struct mm_struct *mm) 34 { 35 void *pte_frag, *ret; 36 37 if (PTE_FRAG_NR == 1) 38 return NULL; 39 40 spin_lock(&mm->page_table_lock); 41 ret = pte_frag_get(&mm->context); 42 if (ret) { 43 pte_frag = ret + PTE_FRAG_SIZE; 44 /* 45 * If we have taken up all the fragments mark PTE page NULL 46 */ 47 if (((unsigned long)pte_frag & ~PAGE_MASK) == 0) 48 pte_frag = NULL; 49 pte_frag_set(&mm->context, pte_frag); 50 } 51 spin_unlock(&mm->page_table_lock); 52 return (pte_t *)ret; 53 } 54 55 static pte_t *__alloc_for_ptecache(struct mm_struct *mm, int kernel) 56 { 57 void *ret = NULL; 58 struct ptdesc *ptdesc; 59 gfp_t gfp = PGALLOC_GFP; 60 61 if (!kernel) 62 gfp |= __GFP_ACCOUNT; 63 64 ptdesc = pagetable_alloc(gfp, 0); 65 if (!ptdesc) 66 return NULL; 67 if (!pagetable_pte_ctor(mm, ptdesc)) { 68 pagetable_free(ptdesc); 69 return NULL; 70 } 71 72 atomic_set(&ptdesc->pt_frag_refcount, 1); 73 74 ret = ptdesc_address(ptdesc); 75 /* 76 * if we support only one fragment just return the 77 * allocated page. 78 */ 79 if (PTE_FRAG_NR == 1) 80 return ret; 81 spin_lock(&mm->page_table_lock); 82 /* 83 * If we find ptdesc_page set, we return 84 * the allocated page with single fragment 85 * count. 86 */ 87 if (likely(!pte_frag_get(&mm->context))) { 88 atomic_set(&ptdesc->pt_frag_refcount, PTE_FRAG_NR); 89 pte_frag_set(&mm->context, ret + PTE_FRAG_SIZE); 90 } 91 spin_unlock(&mm->page_table_lock); 92 93 return (pte_t *)ret; 94 } 95 96 pte_t *pte_fragment_alloc(struct mm_struct *mm, int kernel) 97 { 98 pte_t *pte; 99 100 pte = get_pte_from_cache(mm); 101 if (pte) 102 return pte; 103 104 return __alloc_for_ptecache(mm, kernel); 105 } 106 107 static void pte_free_now(struct rcu_head *head) 108 { 109 struct ptdesc *ptdesc; 110 111 ptdesc = container_of(head, struct ptdesc, pt_rcu_head); 112 pagetable_dtor(ptdesc); 113 pagetable_free(ptdesc); 114 } 115 116 void pte_fragment_free(unsigned long *table, int kernel) 117 { 118 struct ptdesc *ptdesc = virt_to_ptdesc(table); 119 120 if (pagetable_is_reserved(ptdesc)) 121 return free_reserved_ptdesc(ptdesc); 122 123 BUG_ON(atomic_read(&ptdesc->pt_frag_refcount) <= 0); 124 if (atomic_dec_and_test(&ptdesc->pt_frag_refcount)) { 125 if (kernel || !folio_test_clear_active(ptdesc_folio(ptdesc))) 126 pte_free_now(&ptdesc->pt_rcu_head); 127 else 128 call_rcu(&ptdesc->pt_rcu_head, pte_free_now); 129 } 130 } 131 132 #ifdef CONFIG_TRANSPARENT_HUGEPAGE 133 void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable) 134 { 135 struct folio *folio; 136 137 folio = virt_to_folio(pgtable); 138 folio_set_active(folio); 139 pte_fragment_free((unsigned long *)pgtable, 0); 140 } 141 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ 142