内核页表初始化

上个视频

1. entry.S 开启分页 CR0_PG
2. main():kinit1 -> freelist

   (qemu) info tlb
   0000000000000000: 0000000000000000 --P-A---W
   0000000080000000: 0000000000000000 --PDA---W
   (qemu) info mem
   0000000000000000-0000000000400000 0000000000400000 -rw
   0000000080000000-0000000080400000 0000000000400000 -rw
   (qemu)
       

   (gdb) xv-freelist
   #1: 0x803ff000 -> use
   #2: 0x803fe000 -> use
   #3: 0x803fd000
   #4: 0x803fc000
   #5: 0x803fb000
   #6: 0x803fa000
   #7: 0x803f9000
   #8: 0x803f8000
   #9: 0x803f7000
   total=746 size=746.00M 782237696
       

   (gdb) p/x kmap
   $6 = {
     {virt = 0x80000000, phys_start = 0x0, phys_end = 0x100000, perm = 0x2},
     {virt = 0x80100000, phys_start = 0x100000, phys_end = 0x108000, perm = 0x0},
     {virt = 0x80108000, phys_start = 0x108000, phys_end = 0xe000000, perm = 0x2},
     {virt = 0xfe000000, phys_start = 0xfe000000, phys_end = 0x0, perm = 0x2}
   }
       

kvmalloc 初始化页表

kvmalloc 初始化内存页表，核心调研 setupkvm 初始化内核分页表

• kalloc 申请 4K 物理页
  1. pgdir 页目录
• memset 设置内存值
• mappages 初始化页表项, 初始化 kmap
  1. walkpgdir 创建页表项
  2. 设置权限

(gdb) p pgdir
$10 = (pde_t *) 0x803ff000
(gdb) x/8x 0x803ff000
0x803ff000:     0x803fe000      0x01010101      0x01010101      0x01010101
0x803ff010:     0x01010101      0x01010101      0x01010101      0x01010101
(gdb) set print array on
(gdb) p/x kmap
$4 = {
  {virt = 0x80000000, phys_start = 0x0, phys_end = 0x100000, perm = 0x2},
  {virt = 0x80100000, phys_start = 0x100000, phys_end = 0x108000, perm = 0x0},
  {virt = 0x80108000, phys_start = 0x108000, phys_end = 0xe000000, perm = 0x2},
  {virt = 0xfe000000, phys_start = 0xfe000000, phys_end = 0x0, perm = 0x2}
}
(gdb)

物理内存分布

1. 0x0 ~ 0x100000: BIOS 地址空间 (total 1MB)
   • 0x7c00 ~ 0x7e00 MBR
   • 0xa0000 ~ 0x100000 device memory region
2. EXTMEM(0x100000) ~ end: BIOS extended memory start
   • kernel text+data
   • end 0x1154d0 in main.c
3. end ~ PHYSTOP(0xe000000): Free Memory
   • end ~ 4M kinit1 初始化
   • PHYSTOP 物理内存终点, kmap 定义, kvmalloc 中初始化
4. DEVSPACE(0xfe000000) ~ 4G: Memory-mapped 32-bit I/O Devices
   • DEVSPACE memory mapped direct
   • devices such as ioapic