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
18void pte_frag_destroy(void *pte_frag)
19{
20 int count;
21 struct ptdesc *ptdesc;
22
23 ptdesc = virt_to_ptdesc(x: 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(i: PTE_FRAG_NR - count, v: &ptdesc->pt_frag_refcount)) {
28 pagetable_pte_dtor(ptdesc);
29 pagetable_free(pt: ptdesc);
30 }
31}
32
33static 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(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(lock: &mm->page_table_lock);
52 return (pte_t *)ret;
53}
54
55static 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(gfp: PGALLOC_GFP | __GFP_ACCOUNT, order: 0);
62 if (!ptdesc)
63 return NULL;
64 if (!pagetable_pte_ctor(ptdesc)) {
65 pagetable_free(pt: ptdesc);
66 return NULL;
67 }
68 } else {
69 ptdesc = pagetable_alloc(gfp: PGALLOC_GFP, order: 0);
70 if (!ptdesc)
71 return NULL;
72 }
73
74 atomic_set(v: &ptdesc->pt_frag_refcount, i: 1);
75
76 ret = ptdesc_address(pt: 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(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(v: &ptdesc->pt_frag_refcount, i: PTE_FRAG_NR);
91 pte_frag_set(&mm->context, ret + PTE_FRAG_SIZE);
92 }
93 spin_unlock(lock: &mm->page_table_lock);
94
95 return (pte_t *)ret;
96}
97
98pte_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
109static 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(pt: ptdesc);
116}
117
118void pte_fragment_free(unsigned long *table, int kernel)
119{
120 struct ptdesc *ptdesc = virt_to_ptdesc(x: table);
121
122 if (pagetable_is_reserved(pt: ptdesc))
123 return free_reserved_ptdesc(pt: ptdesc);
124
125 BUG_ON(atomic_read(&ptdesc->pt_frag_refcount) <= 0);
126 if (atomic_dec_and_test(v: &ptdesc->pt_frag_refcount)) {
127 if (kernel)
128 pagetable_free(pt: ptdesc);
129 else if (folio_test_clear_active(ptdesc_folio(ptdesc)))
130 call_rcu(head: &ptdesc->pt_rcu_head, func: pte_free_now);
131 else
132 pte_free_now(head: &ptdesc->pt_rcu_head);
133 }
134}
135
136#ifdef CONFIG_TRANSPARENT_HUGEPAGE
137void 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(table: (unsigned long *)pgtable, kernel: 0);
144}
145#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
146

source code of linux/arch/powerpc/mm/pgtable-frag.c