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Diffstat (limited to 'kernel/mm/virtual_mm/virtual_mm.cc')
| -rw-r--r-- | kernel/mm/virtual_mm/virtual_mm.cc | 220 |
1 files changed, 220 insertions, 0 deletions
diff --git a/kernel/mm/virtual_mm/virtual_mm.cc b/kernel/mm/virtual_mm/virtual_mm.cc new file mode 100644 index 0000000..2293083 --- /dev/null +++ b/kernel/mm/virtual_mm/virtual_mm.cc @@ -0,0 +1,220 @@ +/* + * bubbl + * Copyright (C) 2025 Raghuram Subramani <raghus2247@gmail.com> + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation, either version 3 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ + +#include <kernel/halt.h> +#include <libk/stdio.h> +#include <mm/physical_mm.h> +#include <mm/virtual_mm.h> +#include <stdbool.h> +#include <stdint.h> + +namespace VirtualMM +{ + +extern uint32_t kernel_start; +extern uint32_t kernel_end; + +uint32_t *current_page_directory = 0; + +/* Kernel's page directory */ +uint32_t page_directory[1024] ALIGNED(4096); +/* Page table for the first 4 MiB */ +uint32_t page_table[1024] ALIGNED(4096); + +ALWAYS_INLINE void +load_page_directory(uint32_t *page_directory) +{ + __asm__("movl %0, %%cr3" ::"r"(page_directory)); +} + +bool +switch_page_directory(uint32_t *page_directory) +{ + if (!page_directory) + return false; + current_page_directory = page_directory; + load_page_directory(page_directory); + + return true; +} + +ALWAYS_INLINE static void +enable_paging(void) +{ + __asm__("movl %%cr0, %%eax;" + "orl $0x80000000, %%eax;" + "movl %%eax, %%cr0" :: + : "eax"); +} + +void +init(void) +{ + for (uint32_t i = 0; i < 1024; i++) + page_table[i] = 0; + + /* Identity map the first 4MiB, excluding the 4th MiB + * (maps 4KiB 1024 times) */ + for (uint32_t i = 0; i < 1024; i++) + page_table[i] = PTE_FRAME(i) | PTE_PRESENT(1) | PTE_WRITABLE(1); + + for (uint32_t i = 0; i < 1024; i++) + page_directory[i] = 0; + + uint32_t *pd_entry = &page_directory[0]; + *pd_entry + = PDE_FRAME((uint32_t) page_table) | PDE_PRESENT(1) | PDE_WRITABLE(1); + + switch_page_directory(page_directory); + enable_paging(); +} + +ALWAYS_INLINE uint32_t * +get_or_make_table(uint32_t *pd_entry) +{ + uint32_t *table; + if (!PDE_IS_PRESENT(pd_entry)) { + table = (uint32_t *) PhysicalMM::allocate_block(); + if (!table) + ASSERT_NOT_REACHED(); + + for (uint32_t i = 0; i < 1024; i++) + table[i] = 0x0; + + *pd_entry = PDE_FRAME((uint32_t) table) | PDE_PRESENT(1) | PDE_WRITABLE(1); + } else + table = (uint32_t *) PDE_GET_TABLE(pd_entry); + + return table; +} + +void +map_page(void *physical_address, void *virtual_address) +{ + uint32_t *pd_entry = ¤t_page_directory[GET_PD_INDEX(virtual_address)]; + uint32_t *table = get_or_make_table(pd_entry); + + uint32_t *pt_entry = &table[GET_PT_INDEX(virtual_address)]; + if (PTE_IS_PRESENT(pt_entry)) { + printk("debug", "Mapping previously mapped memory: 0x%x", pt_entry); + ASSERT_NOT_REACHED(); + } + + *pt_entry = PTE_FRAME((uint32_t) physical_address) | PTE_PRESENT(1) + | PTE_WRITABLE(1); +} + +void +unmap_page(void *virtual_address) +{ + uint32_t *pd_entry = ¤t_page_directory[GET_PD_INDEX(virtual_address)]; + + uint32_t *table = 0; + /* If the pd_entry isn't present, return */ + if (!PDE_IS_PRESENT(pd_entry)) + return; + + table = (uint32_t *) PDE_GET_TABLE(pd_entry); + + uint32_t *pt_entry = &table[GET_PT_INDEX(virtual_address)]; + printk("debug", "Freeing: 0x%x", pt_entry); + *pt_entry = 0; +} + +void * +find_free_addresses(uint32_t n) +{ + /* Skip the first page directory, we don't wanna touch the first 4MiB. */ + for (uint32_t pd_index = 1; pd_index < PAGE_DIRECTORY_SIZE; pd_index++) { + uint32_t starting_pd_index = pd_index; + uint32_t *pd_entry = ¤t_page_directory[pd_index]; + uint32_t *table = 0; + + bool table_is_present = PDE_IS_PRESENT(pd_entry); + if (!table_is_present) + table = (uint32_t *) PDE_GET_TABLE(pd_entry); + + for (uint32_t starting_pt_index = 0; starting_pt_index < PAGE_TABLE_SIZE; + starting_pt_index++) { + uint32_t count = 0; + if (table_is_present) + if (PTE_IS_PRESENT(&table[starting_pt_index])) + continue; + + /* We found our starting pt_entry */ + for (uint32_t pt_index = starting_pt_index; pt_index <= PAGE_TABLE_SIZE; + pt_index++) { + /* If we overflow, switch to the consecutive page directory entry */ + if (pt_index == PAGE_TABLE_SIZE) { + pd_index++; + if (pd_index == PAGE_DIRECTORY_SIZE) + return 0; /* Ran out of pd_entries */ + + pd_entry = ¤t_page_directory[pd_index]; + table_is_present = PDE_IS_PRESENT(pd_entry); + pt_index = 0; + } + + if (table_is_present) { + if (PTE_IS_PRESENT(&table[pt_index])) { + /* Since we have some used address at some point between j and + * count, we can't find n consecutive free addresses in between j + * and the used block (j + count + 1) */ + starting_pt_index += count; + break; + } + + count++; + } else + count++; + + if (count == n) + return (void *) VIRTUAL_ADDRESS(starting_pd_index, + starting_pt_index); + } + } + } + + ASSERT_NOT_REACHED(); + return 0; +} + +void * +alloc_pages(uint32_t n_pages) +{ + uint32_t starting_address = (uint32_t) find_free_addresses(n_pages); + if (starting_address == 0) + return 0; + + for (uint32_t i = 0; i < n_pages; i++) { + void *virtual_address = (void *) (starting_address + (i * PAGE_SIZE)); + void *physical_address = PhysicalMM::allocate_block(); + map_page(physical_address, virtual_address); + } + + return (void *) starting_address; +} + +void +free_pages(void *starting_address, uint32_t n_pages) +{ + for (uint32_t i = 0; i < n_pages; i++) + unmap_page((void *) (((uint32_t) starting_address) + (i * 4096))); +} + +} |