1 /*
2 * arch/arm/include/asm/pgtable-2level.h
3 *
4 * Copyright (C) 1995-2002 Russell King
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License version 2 as
8 * published by the Free Software Foundation.
9 */
10 #ifndef _ASM_PGTABLE_2LEVEL_H
11 #define _ASM_PGTABLE_2LEVEL_H
12
13 /*
14 * Hardware-wise, we have a two level page table structure, where the first
15 * level has 4096 entries, and the second level has 256 entries. Each entry
16 * is one 32-bit word. Most of the bits in the second level entry are used
17 * by hardware, and there aren't any "accessed" and "dirty" bits.
18 *
19 * Linux on the other hand has a three level page table structure, which can
20 * be wrapped to fit a two level page table structure easily - using the PGD
21 * and PTE only. However, Linux also expects one "PTE" table per page, and
22 * at least a "dirty" bit.
23 *
24 * Therefore, we tweak the implementation slightly - we tell Linux that we
25 * have 2048 entries in the first level, each of which is 8 bytes (iow, two
26 * hardware pointers to the second level.) The second level contains two
27 * hardware PTE tables arranged contiguously, preceded by Linux versions
28 * which contain the state information Linux needs. We, therefore, end up
29 * with 512 entries in the "PTE" level.
30 *
31 * This leads to the page tables having the following layout:
32 *
33 * pgd pte
34 * | |
35 * +--------+
36 * | | +------------+ +0
37 * +- - - - + | Linux pt 0 |
38 * | | +------------+ +1024
39 * +--------+ +0 | Linux pt 1 |
40 * | |-----> +------------+ +2048
41 * +- - - - + +4 | h/w pt 0 |
42 * | |-----> +------------+ +3072
43 * +--------+ +8 | h/w pt 1 |
44 * | | +------------+ +4096
45 *
46 * See L_PTE_xxx below for definitions of bits in the "Linux pt", and
47 * PTE_xxx for definitions of bits appearing in the "h/w pt".
48 *
49 * PMD_xxx definitions refer to bits in the first level page table.
50 *
51 * The "dirty" bit is emulated by only granting hardware write permission
52 * iff the page is marked "writable" and "dirty" in the Linux PTE. This
53 * means that a write to a clean page will cause a permission fault, and
54 * the Linux MM layer will mark the page dirty via handle_pte_fault().
55 * For the hardware to notice the permission change, the TLB entry must
56 * be flushed, and ptep_set_access_flags() does that for us.
57 *
58 * The "accessed" or "young" bit is emulated by a similar method; we only
59 * allow accesses to the page if the "young" bit is set. Accesses to the
60 * page will cause a fault, and handle_pte_fault() will set the young bit
61 * for us as long as the page is marked present in the corresponding Linux
62 * PTE entry. Again, ptep_set_access_flags() will ensure that the TLB is
63 * up to date.
64 *
65 * However, when the "young" bit is cleared, we deny access to the page
66 * by clearing the hardware PTE. Currently Linux does not flush the TLB
67 * for us in this case, which means the TLB will retain the transation
68 * until either the TLB entry is evicted under pressure, or a context
69 * switch which changes the user space mapping occurs.
70 */
71 #define PTRS_PER_PTE 512
72 #define PTRS_PER_PMD 1
73 #define PTRS_PER_PGD 2048
74
75 #define PTE_HWTABLE_PTRS (PTRS_PER_PTE)
76 #define PTE_HWTABLE_OFF (PTE_HWTABLE_PTRS * sizeof(pte_t))
77 #define PTE_HWTABLE_SIZE (PTRS_PER_PTE * sizeof(u32))
78
79 /*
80 * PMD_SHIFT determines the size of the area a second-level page table can map
81 * PGDIR_SHIFT determines what a third-level page table entry can map
82 */
83 #define PMD_SHIFT 21
84 #define PGDIR_SHIFT 21
85
86 #define PMD_SIZE (1UL << PMD_SHIFT)
87 #define PMD_MASK (~(PMD_SIZE-1))
88 #define PGDIR_SIZE (1UL << PGDIR_SHIFT)
89 #define PGDIR_MASK (~(PGDIR_SIZE-1))
90
91 /*
92 * section address mask and size definitions.
93 */
94 #define SECTION_SHIFT 20
95 #define SECTION_SIZE (1UL << SECTION_SHIFT)
96 #define SECTION_MASK (~(SECTION_SIZE-1))
97
98 /*
99 * ARMv6 supersection address mask and size definitions.
100 */
101 #define SUPERSECTION_SHIFT 24
102 #define SUPERSECTION_SIZE (1UL << SUPERSECTION_SHIFT)
103 #define SUPERSECTION_MASK (~(SUPERSECTION_SIZE-1))
104
105 #define USER_PTRS_PER_PGD (TASK_SIZE / PGDIR_SIZE)
106
107 /*
108 * "Linux" PTE definitions.
109 *
110 * We keep two sets of PTEs - the hardware and the linux version.
111 * This allows greater flexibility in the way we map the Linux bits
112 * onto the hardware tables, and allows us to have YOUNG and DIRTY
113 * bits.
114 *
115 * The PTE table pointer refers to the hardware entries; the "Linux"
116 * entries are stored 1024 bytes below.
117 */
118 #define L_PTE_VALID (_AT(pteval_t, 1) << 0) /* Valid */
119 #define L_PTE_PRESENT (_AT(pteval_t, 1) << 0)
120 #define L_PTE_YOUNG (_AT(pteval_t, 1) << 1)
121 #define L_PTE_FILE (_AT(pteval_t, 1) << 2) /* only when !PRESENT */
122 #define L_PTE_DIRTY (_AT(pteval_t, 1) << 6)
123 #define L_PTE_RDONLY (_AT(pteval_t, 1) << 7)
124 #define L_PTE_USER (_AT(pteval_t, 1) << 8)
125 #define L_PTE_XN (_AT(pteval_t, 1) << 9)
126 #define L_PTE_SHARED (_AT(pteval_t, 1) << 10) /* shared(v6), coherent(xsc3) */
127 #define L_PTE_NONE (_AT(pteval_t, 1) << 11)
128
129 /*
130 * These are the memory types, defined to be compatible with
131 * pre-ARMv6 CPUs cacheable and bufferable bits: XXCB
132 */
133 #define L_PTE_MT_UNCACHED (_AT(pteval_t, 0x00) << 2) /* 0000 */
134 #define L_PTE_MT_BUFFERABLE (_AT(pteval_t, 0x01) << 2) /* 0001 */
135 #define L_PTE_MT_WRITETHROUGH (_AT(pteval_t, 0x02) << 2) /* 0010 */
136 #define L_PTE_MT_WRITEBACK (_AT(pteval_t, 0x03) << 2) /* 0011 */
137 #define L_PTE_MT_MINICACHE (_AT(pteval_t, 0x06) << 2) /* 0110 (sa1100, xscale) */
138 #define L_PTE_MT_WRITEALLOC (_AT(pteval_t, 0x07) << 2) /* 0111 */
139 #define L_PTE_MT_DEV_SHARED (_AT(pteval_t, 0x04) << 2) /* 0100 */
140 #define L_PTE_MT_DEV_NONSHARED (_AT(pteval_t, 0x0c) << 2) /* 1100 */
141 #define L_PTE_MT_DEV_WC (_AT(pteval_t, 0x09) << 2) /* 1001 */
142 #define L_PTE_MT_DEV_CACHED (_AT(pteval_t, 0x0b) << 2) /* 1011 */
143 #define L_PTE_MT_VECTORS (_AT(pteval_t, 0x0f) << 2) /* 1111 */
144 #define L_PTE_MT_MASK (_AT(pteval_t, 0x0f) << 2)
145
146 #ifndef __ASSEMBLY__
147
148 /*
149 * The "pud_xxx()" functions here are trivial when the pmd is folded into
150 * the pud: the pud entry is never bad, always exists, and can't be set or
151 * cleared.
152 */
153 #define pud_none(pud) (0)
154 #define pud_bad(pud) (0)
155 #define pud_present(pud) (1)
156 #define pud_clear(pudp) do { } while (0)
157 #define set_pud(pud,pudp) do { } while (0)
158
pmd_offset(pud_t * pud,unsigned long addr)159 static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
160 {
161 return (pmd_t *)pud;
162 }
163
164 #define pmd_large(pmd) (pmd_val(pmd) & 2)
165 #define pmd_bad(pmd) (pmd_val(pmd) & 2)
166 #define pmd_present(pmd) (pmd_val(pmd))
167
168 #define copy_pmd(pmdpd,pmdps) \
169 do { \
170 pmdpd[0] = pmdps[0]; \
171 pmdpd[1] = pmdps[1]; \
172 flush_pmd_entry(pmdpd); \
173 } while (0)
174
175 #define pmd_clear(pmdp) \
176 do { \
177 pmdp[0] = __pmd(0); \
178 pmdp[1] = __pmd(0); \
179 clean_pmd_entry(pmdp); \
180 } while (0)
181
182 /* we don't need complex calculations here as the pmd is folded into the pgd */
183 #define pmd_addr_end(addr,end) (end)
184
185 #define set_pte_ext(ptep,pte,ext) cpu_set_pte_ext(ptep,pte,ext)
186 #define pte_special(pte) (0)
pte_mkspecial(pte_t pte)187 static inline pte_t pte_mkspecial(pte_t pte) { return pte; }
188
189 /*
190 * We don't have huge page support for short descriptors, for the moment
191 * define empty stubs for use by pin_page_for_write.
192 */
193 #define pmd_hugewillfault(pmd) (0)
194 #define pmd_thp_or_huge(pmd) (0)
195
196 #endif /* __ASSEMBLY__ */
197
198 #endif /* _ASM_PGTABLE_2LEVEL_H */
199