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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 <kernel/halt.h>
#include <libk/liballoc.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 *l_current_page_directory = 0;
/* Kernel's page directory */
uint32_t l_page_directory[1024] ALIGNED(4096);
/* Page table for the first 4 MiB */
uint32_t l_fourMiB_page_table[1024] ALIGNED(4096);
/* Page table for the next 4 MiB */
uint32_t l_eightMiB_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;
l_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
initialize(void)
{
/* Zero out the page tables and directories */
for (uint32_t i = 0; i < 1024; i++) {
l_fourMiB_page_table[i] = 0;
l_eightMiB_page_table[i] = 0;
l_page_directory[i] = 0;
}
/* Identity map the first 4MiB, excluding the 4th MiB
* (maps 4KiB 1024 times) */
for (uint32_t i = 0; i < 1024; i++)
l_fourMiB_page_table[i]
= PTE_FRAME(i << 12) | PTE_PRESENT(1) | PTE_WRITABLE(1);
/* Identity map the next 4MiB */
for (uint32_t i = 0; i < 1024; i++)
l_eightMiB_page_table[i]
= PTE_FRAME((i + 1024) << 12) | PTE_PRESENT(1) | PTE_WRITABLE(1);
/* Set up the page directory entries */
uint32_t *fourMiB_pd_entry = &l_page_directory[0];
*fourMiB_pd_entry = PDE_FRAME((uint32_t) l_fourMiB_page_table)
| PDE_PRESENT(1) | PDE_WRITABLE(1);
uint32_t *eightMiB_pd_entry = &l_page_directory[1];
*eightMiB_pd_entry = PDE_FRAME((uint32_t) l_eightMiB_page_table)
| PDE_PRESENT(1) | PDE_WRITABLE(1);
switch_page_directory(l_page_directory);
enable_paging();
}
uint32_t *
make_table(uint32_t *pd_entry)
{
uint32_t *table = 0;
if (!LibAlloc::initialized()) {
/* If we don't have a dynamic memory allocator yet (this will happen only
* once, when we initialize the dynamic allocator), then we hard code the
* next page table to be at 7MiB */
table = (uint32_t *) (7 * MiB);
printk("virtual_mm",
"Using our hard coded table; this should happen only once.");
} else
/* TODO: Uncomment this */
// table = (uint32_t *) LibAlloc::kmalloc(sizeof(uint32_t) * 1024);
;
for (uint32_t i = 0; i < 1024; i++)
table[i] = 0x0;
*pd_entry = PDE_FRAME((uint32_t) table) | PDE_PRESENT(1) | PDE_WRITABLE(1);
return table;
}
ALWAYS_INLINE static uint32_t *
get_or_make_table(uint32_t *pd_entry)
{
uint32_t *table = 0;
if (!PDE_IS_PRESENT(pd_entry))
table = make_table(pd_entry);
else
table = (uint32_t *) PDE_GET_TABLE(pd_entry);
return table;
}
void
map_page(void *physical_address, void *virtual_address)
{
uint32_t *pd_entry
= &l_current_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))
/* Mapping previously mapped memory */
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
= &l_current_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 two page directory entries; we don't wanna touch the first
* 8MiB. */
for (uint32_t pd_index = 2; pd_index < PAGE_DIRECTORY_SIZE; pd_index++) {
uint32_t starting_pd_index = pd_index;
uint32_t *pd_entry = &l_current_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 = &l_current_page_directory[pd_index];
table_is_present = PDE_IS_PRESENT(pd_entry);
pt_index = 0;
}
/* If the table is present, and if the PTE is present, then break */
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;
}
/* TODO: This can be easily optimized if the table is not present.
* (count += 4096, since we know that the table is not present) */
count++;
if (count == n)
return (void *) VIRTUAL_ADDRESS(starting_pd_index,
starting_pt_index);
}
}
}
ASSERT_NOT_REACHED();
return 0;
}
}
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