kern
view src/mem.c @ 46:b793b8fcba7d
apparently free_phys_page was never tested. the check for double-freeing a page
was inverted.
| author | John Tsiombikas <nuclear@member.fsf.org> |
|---|---|
| date | Thu, 28 Jul 2011 05:33:59 +0300 |
| parents | 9939a6d7a45a |
| children |
line source
1 #include <stdio.h>
2 #include <string.h>
3 #include "mem.h"
4 #include "panic.h"
5 #include "vm.h"
6 #include "intr.h"
8 #define FREE 0
9 #define USED 1
11 #define BM_IDX(pg) ((pg) / 32)
12 #define BM_BIT(pg) ((pg) & 0x1f)
14 #define IS_FREE(pg) ((bitmap[BM_IDX(pg)] & (1 << BM_BIT(pg))) == 0)
16 static void mark_page(int pg, int free);
17 static void add_memory(uint32_t start, size_t size);
19 /* end of kernel image */
20 extern int _end;
22 /* A bitmap is used to track which physical memory pages are used or available
23 * for allocation by alloc_phys_page.
24 *
25 * last_alloc_idx keeps track of the last 32bit element in the bitmap array
26 * where a free page was found. It's guaranteed that all the elements before
27 * this have no free pages, but it doesn't imply that there will be another
28 * free page there. So it's used as a starting point for the search.
29 */
30 static uint32_t *bitmap;
31 static int bmsize, last_alloc_idx;
34 void init_mem(struct mboot_info *mb)
35 {
36 int i, num_pages, max_pg = 0;
37 uint32_t used_end;
39 num_pages = 0;
40 last_alloc_idx = 0;
42 /* the allocation bitmap starts right at the end of the ELF image */
43 bitmap = (uint32_t*)&_end;
45 /* start by marking all posible pages (2**20) as used. We do not "reserve"
46 * all this space. Pages beyond the end of the useful bitmap area
47 * ((char*)bitmap + bmsize), which will be determined after we traverse the
48 * memory map, are going to be marked as available for allocation.
49 */
50 memset(bitmap, 0xff, 1024 * 1024 / 8);
52 /* if the bootloader gave us an available memory map, traverse it and mark
53 * all the corresponding pages as free.
54 */
55 if(mb->flags & MB_MMAP) {
56 struct mboot_mmap *mem, *mmap_end;
58 mem = mb->mmap;
59 mmap_end = (struct mboot_mmap*)((char*)mb->mmap + mb->mmap_len);
61 printf("memory map:\n");
62 while(mem < mmap_end) {
63 /* ignore memory ranges that start beyond the 4gb mark */
64 if(mem->base_high == 0 && mem->base_low != 0xffffffff) {
65 char *type;
66 unsigned int end, rest = 0xffffffff - mem->base_low;
68 /* make sure the length does not extend beyond 4gb */
69 if(mem->length_high || mem->length_low > rest) {
70 mem->length_low = rest;
71 }
72 end = mem->base_low + mem->length_low;
74 if(mem->type == MB_MEM_VALID) {
75 type = "free:";
76 add_memory(mem->base_low, mem->length_low);
78 num_pages = ADDR_TO_PAGE(mem->base_low + mem->length_low);
79 if(max_pg < num_pages) {
80 max_pg = num_pages;
81 }
82 } else {
83 type = "hole:";
84 }
86 printf(" %s %x - %x (%u bytes)\n", type, mem->base_low, end, mem->length_low);
87 }
88 mem = (struct mboot_mmap*)((char*)mem + mem->skip + sizeof mem->skip);
89 }
90 } else if(mb->flags & MB_MEM) {
91 /* if we don't have a detailed memory map, just use the lower and upper
92 * memory block sizes to determine which pages should be available.
93 */
94 add_memory(0, mb->mem_lower);
95 add_memory(0x100000, mb->mem_upper * 1024);
96 max_pg = mb->mem_upper / 4;
98 printf("lower memory: %ukb, upper mem: %ukb\n", mb->mem_lower, mb->mem_upper);
99 } else {
100 /* I don't think this should ever happen with a multiboot-compliant boot loader */
101 panic("didn't get any memory info from the boot loader, I give up\n");
102 }
104 bmsize = max_pg / 8; /* size of the useful bitmap in bytes */
106 /* mark all the used pages as ... well ... used */
107 used_end = ((uint32_t)bitmap + bmsize - 1);
109 printf("marking pages up to %x ", used_end);
110 used_end = ADDR_TO_PAGE(used_end);
111 printf("(page: %d) inclusive as used\n", used_end);
113 for(i=0; i<=used_end; i++) {
114 mark_page(i, USED);
115 }
116 }
118 /* alloc_phys_page finds the first available page of physical memory,
119 * marks it as used in the bitmap, and returns its address. If there's
120 * no unused physical page, 0 is returned.
121 */
122 uint32_t alloc_phys_page(void)
123 {
124 int i, idx, max, intr_state;
126 intr_state = get_intr_state();
127 disable_intr();
129 idx = last_alloc_idx;
130 max = bmsize / 4;
132 while(idx <= max) {
133 /* if at least one bit is 0 then we have at least
134 * one free page. find it and allocate it.
135 */
136 if(bitmap[idx] != 0xffffffff) {
137 for(i=0; i<32; i++) {
138 int pg = idx * 32 + i;
140 if(IS_FREE(pg)) {
141 mark_page(pg, USED);
143 last_alloc_idx = idx;
145 /*printf("alloc_phys_page() -> %x (page: %d)\n", PAGE_TO_ADDR(pg), pg);*/
147 set_intr_state(intr_state);
148 return PAGE_TO_ADDR(pg);
149 }
150 }
151 panic("can't happen: alloc_phys_page (mem.c)\n");
152 }
153 idx++;
154 }
156 set_intr_state(intr_state);
157 return 0;
158 }
160 /* free_phys_page marks the physical page which corresponds to the specified
161 * address as free in the allocation bitmap.
162 *
163 * CAUTION: no checks are done that this page should actually be freed or not.
164 * If you call free_phys_page with the address of some part of memory that was
165 * originally reserved due to it being in a memory hole or part of the kernel
166 * image or whatever, it will be subsequently allocatable by alloc_phys_page.
167 */
168 void free_phys_page(uint32_t addr)
169 {
170 int pg = ADDR_TO_PAGE(addr);
171 int bmidx = BM_IDX(pg);
173 int intr_state = get_intr_state();
174 disable_intr();
176 if(IS_FREE(pg)) {
177 panic("free_phys_page(%d): I thought that was already free!\n", pg);
178 }
180 mark_page(pg, FREE);
181 if(bmidx < last_alloc_idx) {
182 last_alloc_idx = bmidx;
183 }
185 set_intr_state(intr_state);
186 }
188 /* this is only ever used by the VM init code to find out what the extends of
189 * the kernel image are, in order to map them 1-1 before enabling paging.
190 */
191 void get_kernel_mem_range(uint32_t *start, uint32_t *end)
192 {
193 if(start) {
194 *start = 0x100000;
195 }
196 if(end) {
197 uint32_t e = (uint32_t)bitmap + bmsize;
199 if(e & PGOFFS_MASK) {
200 *end = (e + 4096) & ~PGOFFS_MASK;
201 } else {
202 *end = e;
203 }
204 }
205 }
207 /* adds a range of physical memory to the available pool. used during init_mem
208 * when traversing the memory map.
209 */
210 static void add_memory(uint32_t start, size_t sz)
211 {
212 int i, szpg, pg;
214 szpg = ADDR_TO_PAGE(sz);
215 pg = ADDR_TO_PAGE(start);
217 for(i=0; i<szpg; i++) {
218 mark_page(pg++, FREE);
219 }
220 }
222 /* maps a page as used or free in the allocation bitmap */
223 static void mark_page(int pg, int used)
224 {
225 int idx = BM_IDX(pg);
226 int bit = BM_BIT(pg);
228 if(used) {
229 bitmap[idx] |= 1 << bit;
230 } else {
231 bitmap[idx] &= ~(1 << bit);
232 }
233 }