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) 158 159 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) 166 167 #define copy_pmd(pmdpd,pmdps) \ 168 do { \ 169 pmdpd[0] = pmdps[0]; \ 170 pmdpd[1] = pmdps[1]; \ 171 flush_pmd_entry(pmdpd); \ 172 } while (0) 173 174 #define pmd_clear(pmdp) \ 175 do { \ 176 pmdp[0] = __pmd(0); \ 177 pmdp[1] = __pmd(0); \ 178 clean_pmd_entry(pmdp); \ 179 } while (0) 180 181 /* we don't need complex calculations here as the pmd is folded into the pgd */ 182 #define pmd_addr_end(addr,end) (end) 183 184 #define set_pte_ext(ptep,pte,ext) cpu_set_pte_ext(ptep,pte,ext) 185 #define pte_special(pte) (0) 186 static inline pte_t pte_mkspecial(pte_t pte) { return pte; } 187 188 /* 189 * We don't have huge page support for short descriptors, for the moment 190 * define empty stubs for use by pin_page_for_write. 191 */ 192 #define pmd_hugewillfault(pmd) (0) 193 #define pmd_thp_or_huge(pmd) (0) 194 195 #endif /* __ASSEMBLY__ */ 196 197 #endif /* _ASM_PGTABLE_2LEVEL_H */ 198