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Diffstat (limited to 'src/kernel/pmap.c')
| -rw-r--r-- | src/kernel/pmap.c | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/src/kernel/pmap.c b/src/kernel/pmap.c new file mode 100644 index 0000000..8634303 --- /dev/null +++ b/src/kernel/pmap.c @@ -0,0 +1,127 @@ +#include <stdint.h> +#include "panic.h" +#include "pmap.h" + +#define PAGEMAP_START (0x00040000) +#define PAGEMAP_END (0x00060000) +#define PAGE_USED(n) ((*(uint8_t *)(PAGEMAP_START + (n >> 3)) >> (n & 7)) & 1) +#define CLEAR_PAGE(n) *(uint8_t *)(PAGEMAP_START + (n >> 3)) &= ~(1 << (n & 7)) +#define SET_PAGE(n) *(uint8_t *)(PAGEMAP_START + (n >> 3)) |= 1 << (n & 7) + +#define KBSS_START (0x04000000) +#define USER_START (0x08000000) +extern const void _kernel_bss_end; + +uint32_t kernel_pages_left; +uint32_t user_pages_left; +uint32_t max_kernel_pages; +uint32_t max_user_pages; + +enum { + BMET_FREE = 1 +}; + +enum { + BMEF_NON_VOLATILE = 0x02 +}; + +struct bios_mmap_entry { + uint64_t base; + uint64_t length; + uint32_t type; + uint32_t flags; +}; + +void init_pagemap() { + for (uint32_t *i = (uint32_t *)(PAGEMAP_START + (KBSS_START >> 15)); i < (uint32_t *)PAGEMAP_END; ++i) + *i = 0xffffffff; + + const struct bios_mmap_entry *mmap_p = (const struct bios_mmap_entry *)0x00010000; + const struct bios_mmap_entry *mmap_e = (const struct bios_mmap_entry *)(0x00010000 + *(uint16_t *)0x00004006); + + for (; mmap_p < mmap_e; ++mmap_p) { + if (mmap_p->type != BMET_FREE) + continue; + if (mmap_p->base > 0xffffffff) + continue; + + uint32_t base_page = ((mmap_p->base - 1) >> 12) + 1; + + uint64_t end = mmap_p->base + mmap_p->length; + if (end > 0xffffffff) + end = 0x100000000; + uint32_t end_page = end >> 12; + + for (uint32_t i = base_page; i < end_page; ++i) + CLEAR_PAGE(i); + } + + uint32_t kernel_pages = (((uint32_t)&_kernel_bss_end - 1) >> 12) + 1; + for (uint32_t i = 0; i < kernel_pages; ++i) + SET_PAGE(i); + + kernel_pages_left = 0; + for (uint32_t i = KBSS_START >> 12; i < USER_START >> 12; ++i) + if (!PAGE_USED(i)) + ++kernel_pages_left; + max_kernel_pages = kernel_pages_left; + + user_pages_left = 0; + for (uint32_t i = USER_START >> 12; i < 1048576; ++i) + if (!PAGE_USED(i)) + ++user_pages_left; + max_user_pages = user_pages_left; +} + +//very inneficient algorithm, just returns first hole big enough. +//a smarter algorithm might pick the smallest one available, +//and go by bytes (or dwords) instead of bits where possible. +void *allocate_kernel_pages(uint32_t n) { + uint32_t run = 0; + + for (uint32_t page = KBSS_START >> 12; page < USER_START >> 12; ++page) { + if (PAGE_USED(page)) + run = 0; + else if (++run == n) { + uint32_t start = page - run + 1; + for (uint32_t i = start; i <= page; ++i) + SET_PAGE(i); + kernel_pages_left -= n; + return (void *)(start << 12); + } + } + + return 0; +} + +//very inneficient algorithm, just returns first hole big enough. +//a smarter algorithm might pick the smallest one available, +//and go by bytes (or dwords) instead of bits where possible. +void *allocate_user_pages(uint32_t n) { + uint32_t run = 0; + + for (uint32_t page = USER_START >> 12; page < 1048576; ++page) { + if (PAGE_USED(page)) + run = 0; + else if (++run == n) { + uint32_t start = page - run + 1; + for (uint32_t i = start; i <= page; ++i) + SET_PAGE(i); + user_pages_left -= n; + return (void *)(start << 12); + } + } + + return 0; +} + +//in the future, change this to go by bytes or dwords instead of bits. +void free_pages(const void *ptr, uint32_t n) { + uint32_t page = (uint32_t)ptr >> 12; + for (uint32_t i = page; i < page + n; ++i) + CLEAR_PAGE(i); + if ((uint32_t)ptr >= USER_START) + user_pages_left += n; + else + kernel_pages_left += n; +}
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