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/*
* 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 <stdint.h>
#include <kernel/halt.h>
#include <libk/stdio.h>
#include <mm/physical_mm.h>
#include <mm/virtual_mm.h>
extern uint32_t kernel_start;
extern uint32_t kernel_end;
uint32_t *current_page_directory = 0;
ALWAYS_INLINE void
virtual_mm_load_page_directory(uint32_t *page_directory)
{
__asm__("movl %0, %%cr3" ::"r"(page_directory));
}
bool
virtual_mm_switch_page_directory(uint32_t *page_directory)
{
if (!page_directory)
return false;
current_page_directory = page_directory;
virtual_mm_load_page_directory(page_directory);
return true;
}
ALWAYS_INLINE static void
virtual_mm_enable_paging(void)
{
__asm__("movl %%cr0, %%eax;"
"orl $0x80000000, %%eax;"
"movl %%eax, %%cr0" ::
: "eax");
}
void
virtual_mm_initialize(void)
{
uint32_t *table = physical_mm_allocate_block();
if (!table)
ASSERT_NOT_REACHED();
for (uint32_t i = 0; i < 1024; i++)
table[i] = 0;
/* Identity map the first 4MiB, excluding the 4th MiB
* (maps 4KiB 1024 times) */
for (uint32_t i = 0; i < 1024; i++)
table[i] = PTE_FRAME(i) | PTE_PRESENT(1) | PTE_WRITABLE(1);
uint32_t *page_directory = physical_mm_allocate_block();
if (!page_directory)
ASSERT_NOT_REACHED();
printk("debug", "Page directory is at: 0x%x", page_directory);
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) table) | PDE_PRESENT(1) | PDE_WRITABLE(1);
virtual_mm_switch_page_directory(page_directory);
virtual_mm_enable_paging();
}
void
virtual_mm_map_page(void *physical_address, 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, allocate a block for it, zero the table,
* and set the pd_entry's frame to the table's address. */
if (!PDE_IS_PRESENT(pd_entry)) {
table = physical_mm_allocate_block();
if (!table)
ASSERT_NOT_REACHED();
for (uint32_t i = 0; i < 1024; i++)
table[i] = 0;
*pd_entry = PDE_FRAME((uint32_t) table) | PDE_PRESENT(1) | PDE_WRITABLE(1);
} else
table = (uint32_t *) PDE_GET_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
virtual_mm_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)];
*pt_entry = 0;
}
ALWAYS_INLINE uint32_t *
get_or_make_table(uint32_t *pd_entry)
{
uint32_t *table;
if (!PDE_IS_PRESENT(pd_entry)) {
table = physical_mm_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;
}
uint32_t
virtual_mm_find_free_virtual_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];
/* Ideally, we shouldn't be allocating tables here */
uint32_t *table = get_or_make_table(pd_entry);
for (uint32_t starting_pt_index = 0; starting_pt_index < PAGE_TABLE_SIZE;
starting_pt_index++) {
uint32_t *pt_entry = &table[starting_pt_index];
if (PTE_IS_PRESENT(pt_entry))
continue;
/* We found our starting pt_entry */
uint32_t count = 0;
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) {
if (++pd_index == PAGE_DIRECTORY_SIZE)
return 0; /* Ran out of pd_entries */
pd_entry = ¤t_page_directory[pd_index];
table = get_or_make_table(pd_entry);
pt_index = 0;
}
/* If page table entry is already used, break from the current loop
*/
uint32_t *pt_entry = &table[pt_index];
if (PTE_IS_PRESENT(pt_entry)) {
/* 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;
}
if (++count == n)
return VIRTUAL_ADDRESS(starting_pd_index, starting_pt_index);
}
}
}
ASSERT_NOT_REACHED();
return 0;
}
void *
virtual_mm_alloc_pages(uint32_t n_pages)
{
uint32_t starting_address = virtual_mm_find_free_virtual_addresses(n_pages);
if (starting_address == 0)
return 0;
for (uint32_t i = 0; i < n_pages; i++)
virtual_mm_map_page(physical_mm_allocate_block(),
(void *) (starting_address + (i * 4096)));
return (void *) starting_address;
}
void
virtual_mm_free_pages(void *starting_address, uint32_t n_pages)
{
for (uint32_t i = 0; i < n_pages; i++)
virtual_mm_unmap_page(
(void *) (((uint32_t) starting_address) + (i * 4096)));
}
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