8 #include "threads/loader.h"
10 /* Virtual to physical translation works like this on an x86:
12 - The top 10 bits of the virtual address (bits 22:31) are used
13 to index into the page directory. If the PDE is marked
14 "present," the physical address of a page table is read from
15 the PDE thus obtained. If the PDE is marked "not present"
16 then a page fault occurs.
18 - The next 10 bits of the virtual address (bits 12:21) are
19 used to index into the page table. If the PTE is marked
20 "present," the physical address of a data page is read from
21 the PTE thus obtained. If the PTE is marked "not present"
22 then a page fault occurs.
24 - The bottom 12 bits of the virtual address (bits 0:11) are
25 added to the data page's physical base address, producing
26 the final physical address.
30 +--------------------------------------------------------------------+
31 | Page Directory Index | Page Table Index | Page Offset |
32 +--------------------------------------------------------------------+
34 _______/ _______/ _____/
36 / Page Directory / Page Table / Data Page
37 / .____________. / .____________. / .____________.
38 |1,023|____________| |1,023|____________| | |____________|
39 |1,022|____________| |1,022|____________| | |____________|
40 |1,021|____________| |1,021|____________| \__\|____________|
41 |1,020|____________| |1,020|____________| /|____________|
44 | | . | /| . | \ | . |
45 \____\| . |_ | . | | | . |
46 /| . | \ | . | | | . |
49 |____________| | |____________| | |____________|
50 4|____________| | 4|____________| | |____________|
51 3|____________| | 3|____________| | |____________|
52 2|____________| | 2|____________| | |____________|
53 1|____________| | 1|____________| | |____________|
54 0|____________| \__\0|____________| \____\|____________|
58 #define MASK(SHIFT, CNT) (((1ul << (CNT)) - 1) << (SHIFT))
60 /* Page offset (bits 0:11). */
61 #define PGSHIFT 0 /* First offset bit. */
62 #define PGBITS 12 /* Number of offset bits. */
63 #define PGMASK MASK(PGSHIFT, PGBITS)
64 #define PGSIZE (1 << PGBITS)
66 /* Page table (bits 12:21). */
67 #define PTSHIFT PGBITS /* First page table bit. */
68 #define PTBITS 10 /* Number of page table bits. */
69 #define PTMASK MASK(PTSHIFT, PTBITS)
71 /* Page directory (bits 22:31). */
72 #define PDSHIFT (PTSHIFT + PTBITS) /* First page dir bit. */
73 #define PDBITS 10 /* Number of page dir bits. */
74 #define PDMASK MASK(PDSHIFT, PDBITS)
76 /* Offset within a page. */
77 static inline unsigned pg_ofs (const void *va) {
78 return (uintptr_t) va & PGMASK;
81 /* Virtual page number. */
82 static inline uintptr_t pg_no (const void *va) {
83 return (uintptr_t) va >> PTSHIFT;
86 /* Round up to nearest page boundary. */
87 static inline void *pg_round_up (const void *va) {
88 return (void *) (((uintptr_t) va + PGSIZE - 1) & ~PGMASK);
91 /* Round down to nearest page boundary. */
92 static inline void *pg_round_down (const void *va) {
93 return (void *) ((uintptr_t) va & ~PGMASK);
96 #define PHYS_BASE ((void *) LOADER_PHYS_BASE)
98 /* Returns kernel virtual address at which physical address PADDR
101 ptov (uintptr_t paddr)
103 ASSERT ((void *) paddr < PHYS_BASE);
105 return (void *) (paddr + PHYS_BASE);
108 /* Returns physical address at which kernel virtual address VADDR
110 static inline uintptr_t
111 vtop (const void *vaddr)
113 ASSERT (vaddr >= PHYS_BASE);
115 return (uintptr_t) vaddr - (uintptr_t) PHYS_BASE;
118 /* Page directories and page tables.
120 For more information see [IA32-v3] pages 3-23 to 3-28.
122 PDEs and PTEs share a common format:
125 +------------------------------------+------------------------+
126 | Physical Address | Flags |
127 +------------------------------------+------------------------+
129 In a PDE, the physical address points to a page table.
130 In a PTE, the physical address points to a data or code page.
131 The important flags are listed below.
132 When a PDE or PTE is not "present", the other flags are
134 A PDE or PTE that is initialized to 0 will be interpreted as
135 "not present", which is just fine. */
136 #define PG_P 0x1 /* 1=present, 0=not present. */
137 #define PG_W 0x2 /* 1=read/write, 0=read-only. */
138 #define PG_U 0x4 /* 1=user/kernel, 0=kernel only. */
139 #define PG_A 0x20 /* 1=accessed, 0=not acccessed. */
140 #define PG_D 0x40 /* 1=dirty, 0=not dirty (PTEs only). */
142 /* Obtains page directory index from a virtual address. */
143 static inline uintptr_t pd_no (const void *va) {
144 return (uintptr_t) va >> PDSHIFT;
147 /* Returns a PDE that points to page table PT. */
148 static inline uint32_t pde_create (uint32_t *pt) {
149 ASSERT (pg_ofs (pt) == 0);
150 return vtop (pt) | PG_U | PG_P | PG_W;
153 /* Returns a pointer to the page table that page directory entry
154 PDE, which must "present", points to. */
155 static inline uint32_t *pde_get_pt (uint32_t pde) {
157 return ptov (pde & ~PGMASK);
160 /* Obtains page table index from a virtual address. */
161 static inline unsigned pt_no (void *va) {
162 return ((uintptr_t) va & PTMASK) >> PTSHIFT;
165 /* Returns a PTE that points to PAGE.
166 The PTE's page is readable.
167 If WRITABLE is true then it will be writable as well.
168 The page will be usable only by ring 0 code (the kernel). */
169 static inline uint32_t pte_create_kernel (uint32_t *page, bool writable) {
170 ASSERT (pg_ofs (page) == 0);
171 return vtop (page) | PG_P | (writable ? PG_W : 0);
174 /* Returns a PTE that points to PAGE.
175 The PTE's page is readable.
176 If WRITABLE is true then it will be writable as well.
177 The page will be usable by both user and kernel code. */
178 static inline uint32_t pte_create_user (uint32_t *page, bool writable) {
179 return pte_create_kernel (page, writable) | PG_U;
182 /* Returns a pointer to the page that page table entry PTE, which
183 must "present", points to. */
184 static inline void *pte_get_page (uint32_t pte) {
186 return ptov (pte & ~PGMASK);
189 #endif /* threads/mmu.h */