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 /* Base address of the 1:1 physical-to-virtual mapping. Physical
97 memory is mapped starting at this virtual address. Thus,
98 physical address 0 is accessible at PHYS_BASE, physical
99 address address 0x1234 at (uint8_t *) PHYS_BASE + 0x1234, and
102 This address also marks the end of user programs' address
103 space. Up to this point in memory, user programs are allowed
104 to map whatever they like. At this point and above, the
105 virtual address space belongs to the kernel. */
106 #define PHYS_BASE ((void *) LOADER_PHYS_BASE)
108 /* Returns kernel virtual address at which physical address PADDR
111 ptov (uintptr_t paddr)
113 ASSERT ((void *) paddr < PHYS_BASE);
115 return (void *) (paddr + PHYS_BASE);
118 /* Returns physical address at which kernel virtual address VADDR
120 static inline uintptr_t
121 vtop (const void *vaddr)
123 ASSERT (vaddr >= PHYS_BASE);
125 return (uintptr_t) vaddr - (uintptr_t) PHYS_BASE;
128 /* Page directories and page tables.
130 For more information see [IA32-v3] pages 3-23 to 3-28.
132 PDEs and PTEs share a common format:
135 +------------------------------------+------------------------+
136 | Physical Address | Flags |
137 +------------------------------------+------------------------+
139 In a PDE, the physical address points to a page table.
140 In a PTE, the physical address points to a data or code page.
141 The important flags are listed below.
142 When a PDE or PTE is not "present", the other flags are
144 A PDE or PTE that is initialized to 0 will be interpreted as
145 "not present", which is just fine. */
146 #define PG_P 0x1 /* 1=present, 0=not present. */
147 #define PG_W 0x2 /* 1=read/write, 0=read-only. */
148 #define PG_U 0x4 /* 1=user/kernel, 0=kernel only. */
149 #define PG_A 0x20 /* 1=accessed, 0=not acccessed. */
150 #define PG_D 0x40 /* 1=dirty, 0=not dirty (PTEs only). */
152 /* Obtains page directory index from a virtual address. */
153 static inline uintptr_t pd_no (const void *va) {
154 return (uintptr_t) va >> PDSHIFT;
157 /* Returns a PDE that points to page table PT. */
158 static inline uint32_t pde_create (uint32_t *pt) {
159 ASSERT (pg_ofs (pt) == 0);
160 return vtop (pt) | PG_U | PG_P | PG_W;
163 /* Returns a pointer to the page table that page directory entry
164 PDE, which must "present", points to. */
165 static inline uint32_t *pde_get_pt (uint32_t pde) {
167 return ptov (pde & ~PGMASK);
170 /* Obtains page table index from a virtual address. */
171 static inline unsigned pt_no (void *va) {
172 return ((uintptr_t) va & PTMASK) >> PTSHIFT;
175 /* Returns a PTE that points to PAGE.
176 The PTE's page is readable.
177 If WRITABLE is true then it will be writable as well.
178 The page will be usable only by ring 0 code (the kernel). */
179 static inline uint32_t pte_create_kernel (uint32_t *page, bool writable) {
180 ASSERT (pg_ofs (page) == 0);
181 return vtop (page) | PG_P | (writable ? PG_W : 0);
184 /* Returns a PTE that points to PAGE.
185 The PTE's page is readable.
186 If WRITABLE is true then it will be writable as well.
187 The page will be usable by both user and kernel code. */
188 static inline uint32_t pte_create_user (uint32_t *page, bool writable) {
189 return pte_create_kernel (page, writable) | PG_U;
192 /* Returns a pointer to the page that page table entry PTE, which
193 must "present", points to. */
194 static inline void *pte_get_page (uint32_t pte) {
196 return ptov (pte & ~PGMASK);
199 #endif /* threads/mmu.h */