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_pte_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
60 if (!kernel) {
61 ptdesc = pagetable_alloc(PGALLOC_GFP | __GFP_ACCOUNT, 0);
62 if (!ptdesc)
63 return NULL;
64 if (!pagetable_pte_ctor(ptdesc)) {
65 pagetable_free(ptdesc);
66 return NULL;
67 }
68 } else {
69 ptdesc = pagetable_alloc(PGALLOC_GFP, 0);
70 if (!ptdesc)
71 return NULL;
72 }
73
74 atomic_set(&ptdesc->pt_frag_refcount, 1);
75
76 ret = ptdesc_address(ptdesc);
77 /*
78 * if we support only one fragment just return the
79 * allocated page.
80 */
81 if (PTE_FRAG_NR == 1)
82 return ret;
83 spin_lock(&mm->page_table_lock);
84 /*
85 * If we find ptdesc_page set, we return
86 * the allocated page with single fragment
87 * count.
88 */
89 if (likely(!pte_frag_get(&mm->context))) {
90 atomic_set(&ptdesc->pt_frag_refcount, PTE_FRAG_NR);
91 pte_frag_set(&mm->context, ret + PTE_FRAG_SIZE);
92 }
93 spin_unlock(&mm->page_table_lock);
94
95 return (pte_t *)ret;
96 }
97
98 pte_t *pte_fragment_alloc(struct mm_struct *mm, int kernel)
99 {
100 pte_t *pte;
101
102 pte = get_pte_from_cache(mm);
103 if (pte)
104 return pte;
105
106 return __alloc_for_ptecache(mm, kernel);
107 }
108
109 static void pte_free_now(struct rcu_head *head)
110 {
111 struct ptdesc *ptdesc;
112
113 ptdesc = container_of(head, struct ptdesc, pt_rcu_head);
114 pagetable_pte_dtor(ptdesc);
115 pagetable_free(ptdesc);
116 }
117
118 void pte_fragment_free(unsigned long *table, int kernel)
119 {
120 struct ptdesc *ptdesc = virt_to_ptdesc(table);
121
122 if (pagetable_is_reserved(ptdesc))
123 return free_reserved_ptdesc(ptdesc);
124
125 BUG_ON(atomic_read(&ptdesc->pt_frag_refcount) <= 0);
126 if (atomic_dec_and_test(&ptdesc->pt_frag_refcount)) {
127 if (kernel)
128 pagetable_free(ptdesc);
129 else if (folio_test_clear_active(ptdesc_folio(ptdesc)))
130 call_rcu(&ptdesc->pt_rcu_head, pte_free_now);
131 else
132 pte_free_now(&ptdesc->pt_rcu_head);
133 }
134 }
135
136 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
137 void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
138 {
139 struct page *page;
140
141 page = virt_to_page(pgtable);
142 SetPageActive(page);
143 pte_fragment_free((unsigned long *)pgtable, 0);
144 }
145 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
146
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