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 22:32) 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 12:22) 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 0:12) 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 0:12). */
61 #define PGSHIFT 0 /* Index of first offset bit. */
62 #define PGBITS 12 /* Number of offset bits. */
63 #define PGMASK MASK(PGSHIFT, PGBITS) /* Page offset bits (0:12). */
64 #define PGSIZE (1 << PGBITS) /* Bytes in a page. */
66 /* Page table (bits 12:22). */
67 #define PTSHIFT PGBITS /* Index of first page table bit. */
68 #define PTBITS 10 /* Number of page table bits. */
69 #define PTMASK MASK(PTSHIFT, PTBITS) /* Page table bits (12:22). */
70 #define PTSPAN (1 << PTBITS << PGBITS) /* Bytes covered by a page table. */
72 /* Page directory (bits 22:32). */
73 #define PDSHIFT (PTSHIFT + PTBITS) /* First page dir bit. */
74 #define PDBITS 10 /* Number of page dir bits. */
75 #define PDMASK MASK(PDSHIFT, PDBITS) /* Page directory bits (22:32). */
77 /* Offset within a page. */
78 static inline unsigned pg_ofs (const void *va) {
79 return (uintptr_t) va & PGMASK;
82 /* Virtual page number. */
83 static inline uintptr_t pg_no (const void *va) {
84 return (uintptr_t) va >> PTSHIFT;
87 /* Round up to nearest page boundary. */
88 static inline void *pg_round_up (const void *va) {
89 return (void *) (((uintptr_t) va + PGSIZE - 1) & ~PGMASK);
92 /* Round down to nearest page boundary. */
93 static inline void *pg_round_down (const void *va) {
94 return (void *) ((uintptr_t) va & ~PGMASK);
97 /* Base address of the 1:1 physical-to-virtual mapping. Physical
98 memory is mapped starting at this virtual address. Thus,
99 physical address 0 is accessible at PHYS_BASE, physical
100 address address 0x1234 at (uint8_t *) PHYS_BASE + 0x1234, and
103 This address also marks the end of user programs' address
104 space. Up to this point in memory, user programs are allowed
105 to map whatever they like. At this point and above, the
106 virtual address space belongs to the kernel. */
107 #define PHYS_BASE ((void *) LOADER_PHYS_BASE)
109 /* Returns kernel virtual address at which physical address PADDR
112 ptov (uintptr_t paddr)
114 ASSERT ((void *) paddr < PHYS_BASE);
116 return (void *) (paddr + PHYS_BASE);
119 /* Returns physical address at which kernel virtual address VADDR
121 static inline uintptr_t
122 vtop (const void *vaddr)
124 ASSERT (vaddr >= PHYS_BASE);
126 return (uintptr_t) vaddr - (uintptr_t) PHYS_BASE;
129 /* Page directories and page tables.
131 For more information see [IA32-v3] pages 3-23 to 3-28.
133 PDEs and PTEs share a common format:
136 +------------------------------------+------------------------+
137 | Physical Address | Flags |
138 +------------------------------------+------------------------+
140 In a PDE, the physical address points to a page table.
141 In a PTE, the physical address points to a data or code page.
142 The important flags are listed below.
143 When a PDE or PTE is not "present", the other flags are
145 A PDE or PTE that is initialized to 0 will be interpreted as
146 "not present", which is just fine. */
147 #define PG_P 0x1 /* 1=present, 0=not present. */
148 #define PG_W 0x2 /* 1=read/write, 0=read-only. */
149 #define PG_U 0x4 /* 1=user/kernel, 0=kernel only. */
150 #define PG_A 0x20 /* 1=accessed, 0=not acccessed. */
151 #define PG_D 0x40 /* 1=dirty, 0=not dirty (PTEs only). */
153 /* Obtains page directory index from a virtual address. */
154 static inline uintptr_t pd_no (const void *va) {
155 return (uintptr_t) va >> PDSHIFT;
158 /* Returns a PDE that points to page table PT. */
159 static inline uint32_t pde_create (uint32_t *pt) {
160 ASSERT (pg_ofs (pt) == 0);
161 return vtop (pt) | PG_U | PG_P | PG_W;
164 /* Returns a pointer to the page table that page directory entry
165 PDE, which must "present", points to. */
166 static inline uint32_t *pde_get_pt (uint32_t pde) {
168 return ptov (pde & ~PGMASK);
171 /* Obtains page table index from a virtual address. */
172 static inline unsigned pt_no (void *va) {
173 return ((uintptr_t) va & PTMASK) >> PTSHIFT;
176 /* Returns a PTE that points to PAGE.
177 The PTE's page is readable.
178 If WRITABLE is true then it will be writable as well.
179 The page will be usable only by ring 0 code (the kernel). */
180 static inline uint32_t pte_create_kernel (uint32_t *page, bool writable) {
181 ASSERT (pg_ofs (page) == 0);
182 return vtop (page) | PG_P | (writable ? PG_W : 0);
185 /* Returns a PTE that points to PAGE.
186 The PTE's page is readable.
187 If WRITABLE is true then it will be writable as well.
188 The page will be usable by both user and kernel code. */
189 static inline uint32_t pte_create_user (uint32_t *page, bool writable) {
190 return pte_create_kernel (page, writable) | PG_U;
193 /* Returns a pointer to the page that page table entry PTE, which
194 must "present", points to. */
195 static inline void *pte_get_page (uint32_t pte) {
197 return ptov (pte & ~PGMASK);
200 #endif /* threads/mmu.h */