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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_PDE_FRAME(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_PTE_FRAME(virtual_address)];
if (PTE_IS_PRESENT(pt_entry))
ASSERT_NOT_REACHED(); /* TODO: Mapping previously mapped memory */
*pt_entry = PTE_FRAME((uint32_t) physical_address) | PTE_PRESENT(1)
| PTE_WRITABLE(1);
}
ALWAYS_INLINE uint32_t *
get_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 _ = 0; _ < 1024; _++)
table[_] = 0;
*pd_entry = PDE_FRAME((uint32_t) table) | PDE_PRESENT(1) | PDE_WRITABLE(1);
} else
table = (uint32_t *) PDE_GET_TABLE(pd_entry);
return table;
}
ALWAYS_INLINE void
virtual_mm_find_free_virtual_addresses(uint32_t n)
{
for (uint32_t i = 0; i < PAGE_DIRECTORY_SIZE; i++) {
uint32_t current_pd_index = i;
uint32_t *pd_entry = ¤t_page_directory[current_pd_index];
uint32_t *table = get_table(pd_entry);
for (uint32_t j = 0; j < PAGE_TABLE_SIZE; j++) {
uint32_t *pt_entry = &table[j];
if (PTE_IS_PRESENT(pt_entry))
continue;
/* We found our starting pt_entry */
printk("debug", "Starting: 0x%x", pt_entry);
uint32_t count = 0;
for (uint32_t k = j; k <= PAGE_TABLE_SIZE; k++) {
/* If we overflow, switch to the consecutive page directory entry */
if (k == PAGE_TABLE_SIZE) {
pd_entry = ¤t_page_directory[++current_pd_index];
table = get_table(pd_entry);
printk("debug", "Switching pd_entry: 0x%x", pd_entry);
k = 0;
}
uint32_t *pt_entry = &table[k];
if (PTE_IS_PRESENT(pt_entry)) {
count = 0;
current_pd_index = i;
pd_entry = ¤t_page_directory[current_pd_index];
j += count;
break;
}
// printk("debug", "Found page: 0x%x", &table[k]);
count++;
if (count == n) {
printk("debug", "Found starting page at: 0x%x", &table[j]);
return;
}
}
}
}
}
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