along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include <stdio.h>
+#include <string.h>
#include "panic.h"
#include "mem.h"
+#include "intr.h"
+
+#define FREE 0
+#define USED 1
+
+#define BM_IDX(pg) ((pg) / 32)
+#define BM_BIT(pg) ((pg) & 0x1f)
+
+#define IS_FREE(pg) ((bitmap[BM_IDX(pg)] & (1 << BM_BIT(pg))) == 0)
+
+#define MEM_START ((uint32_t)&_mem_start)
+
struct mem_range {
uint32_t start;
uint32_t size;
};
+static void mark_page(int pg, int used);
+static void add_memory(uint32_t start, size_t size);
+
#define MAX_MAP_SIZE 16
extern struct mem_range boot_mem_map[MAX_MAP_SIZE];
extern int boot_mem_map_size;
+/* linker supplied symbol, points to the end of the kernel image */
+extern uint32_t _mem_start;
+
+
+/* A bitmap is used to track which physical memory pages are used, and which
+ * are available for allocation by alloc_phys_page.
+ *
+ * last_alloc_idx keeps track of the last 32bit element in the bitmap array
+ * where a free page was found. It's guaranteed that all the elements before
+ * this have no free pages, but it doesn't imply that there will be another
+ * free page there. So it's used as a starting point for the search.
+ */
+static uint32_t *bitmap;
+static int bmsize, last_alloc_idx;
+
+
+
void init_mem(void)
{
- int i;
+ int i, pg, max_pg = 0;
+ uint32_t used_end, start, end, sz, total = 0, rem;
+ const char *suffix[] = {"bytes", "KB", "MB", "GB"};
+
+ last_alloc_idx = 0;
+
+ /* the allocation bitmap starts right at the end of the kernel image */
+ bitmap = (uint32_t*)&_mem_start;
+
+ /* start by marking all posible pages (2**20) as used. We do not "reserve"
+ * all this space. Pages beyond the end of the useful bitmap area
+ * ((char*)bitmap + bmsize), which will be determined after we traverse the
+ * memory map, are going to be marked as available for allocation.
+ */
+ memset(bitmap, 0xff, 1024 * 1024 / 8);
+
if(boot_mem_map_size <= 0 || boot_mem_map_size > MAX_MAP_SIZE) {
panic("invalid memory map size reported by the boot loader: %d\n", boot_mem_map_size);
for(i=0; i<boot_mem_map_size; i++) {
printf(" start: %08x - size: %08x\n", (unsigned int)boot_mem_map[i].start,
(unsigned int)boot_mem_map[i].size);
+
+ start = boot_mem_map[i].start;
+ sz = boot_mem_map[i].size & 0xfffffffc;
+ end = start + sz;
+ if(end < sz) {
+ end = 0xfffffffc;
+ sz = end - start;
+ }
+
+ /* ignore any memory ranges which end before the end of the kernel image */
+ if(end < MEM_START) continue;
+ if(start < MEM_START) {
+ start = MEM_START;
+ }
+
+ add_memory(start, sz);
+ total += sz;
+
+ pg = ADDR_TO_PAGE(end);
+ if(max_pg < pg) {
+ max_pg = pg;
+ }
+ }
+
+ i = 0;
+ while(total > 1024) {
+ rem = total & 0x3ff;
+ total >>= 10;
+ ++i;
+ }
+ printf("Total usable RAM: %u.%u %s\n", total, 100 * rem / 1024, suffix[i]);
+
+ bmsize = max_pg / 8; /* size of the useful bitmap in bytes */
+
+ /* mark all pages occupied by the bitmap as usef */
+ used_end = (uint32_t)bitmap + bmsize - 1;
+
+ printf("marking pages up to %x (page: %d) as used\n", used_end, ADDR_TO_PAGE(used_end));
+
+ for(i=0; i<=used_end; i++) {
+ mark_page(i, USED);
+ }
+}
+
+/* alloc_phys_page finds the first available page of physical memory,
+ * marks it as used in the bitmap, and returns its number. If there's
+ * no unused physical page, -1 is returned.
+ */
+int alloc_ppage(void)
+{
+ int i, idx, max, intr_state;
+
+ intr_state = get_intr_flag();
+ disable_intr();
+
+ idx = last_alloc_idx;
+ max = bmsize / 4;
+
+ while(idx <= max) {
+ /* if at least one bit is 0 then we have at least
+ * one free page. find it and allocate it.
+ */
+ if(bitmap[idx] != 0xffffffff) {
+ for(i=0; i<32; i++) {
+ int pg = idx * 32 + i;
+
+ if(IS_FREE(pg)) {
+ mark_page(pg, USED);
+
+ last_alloc_idx = idx;
+
+ /*printf("alloc_phys_page() -> %x (page: %d)\n", PAGE_TO_ADDR(pg), pg);*/
+
+ set_intr_flag(intr_state);
+ return pg;
+ }
+ }
+ panic("can't happen: alloc_ppage (mem.c)\n");
+ }
+ idx++;
+ }
+
+ set_intr_flag(intr_state);
+ return -1;
+}
+
+/* free_ppage marks the physical page, free in the allocation bitmap.
+ *
+ * CAUTION: no checks are done that this page should actually be freed or not.
+ * If you call free_phys_page with the address of some part of memory that was
+ * originally reserved due to it being in a memory hole or part of the kernel
+ * image or whatever, it will be subsequently allocatable by alloc_phys_page.
+ */
+void free_ppage(int pg)
+{
+ int bmidx = BM_IDX(pg);
+
+ int intr_state = get_intr_flag();
+ disable_intr();
+
+ if(IS_FREE(pg)) {
+ panic("free_ppage(%d): I thought that was already free!\n", pg);
+ }
+
+ mark_page(pg, FREE);
+ if(bmidx < last_alloc_idx) {
+ last_alloc_idx = bmidx;
+ }
+
+ set_intr_flag(intr_state);
+}
+
+
+int alloc_ppage_range(int start, int size)
+{
+ int i, pg = start;
+
+ /* first validate that no page in the requested range is allocated */
+ for(i=0; i<size; i++) {
+ if(!IS_FREE(pg)) {
+ return -1;
+ }
+ ++pg;
+ }
+
+ /* all is well, mark them as used */
+ pg = start;
+ for(i=0; i<size; i++) {
+ mark_page(pg++, USED);
+ }
+ return 0;
+}
+
+int free_ppage_range(int start, int size)
+{
+ int i, pg = start;
+
+ for(i=0; i<size; i++) {
+ free_ppage(pg++);
+ }
+ return 0;
+}
+
+/* adds a range of physical memory to the available pool. used during init_mem
+ * when traversing the memory map.
+ */
+static void add_memory(uint32_t start, size_t sz)
+{
+ int i, szpg, pg;
+
+ szpg = ADDR_TO_PAGE(sz + 4095);
+ pg = ADDR_TO_PAGE(start);
+
+ for(i=0; i<szpg; i++) {
+ mark_page(pg++, FREE);
}
}
+
+/* maps a page as used or free in the allocation bitmap */
+static void mark_page(int pg, int used)
+{
+ int idx = BM_IDX(pg);
+ int bit = BM_BIT(pg);
+
+ if(used) {
+ bitmap[idx] |= 1 << bit;
+ } else {
+ bitmap[idx] &= ~(1 << bit);
+ }
+}
+
projects / bootcensus / commitdiff