boot/x86/stage3/paging.c

   1 /* Code for enabling paging */
   2
   3 #include <stdint.h>
   4
   5 #define ADDRESS_NOT_ALIGNED 1
   6 #define INVL_ADDRESS 2
   7 #define ADDRESS_ALREADY_MAPPED 3
   8 #define ADDRESS_RANGE_MISMATCHED 4
   9
  10 static uint32_t page_directory[1024] __attribute__((aligned(4096))) __attribute__((section(".data")));
  11 static uint32_t page_table_firstmb[1024] __attribute__((aligned(4096))) __attribute__((section(".data")));
  12 static uint32_t page_table_kernel[1024] __attribute__((aligned(4096))) __attribute__((section(".data")));
  13
  14 void enable_paging()
  15 {
  16         int cr3;
  17         asm ("mov %0, %%cr3": : "a" (page_directory));
  18         asm ("mov %%cr0, %0": "=a" (cr3));
  19         cr3 |= 0x80000000;
  20         asm ("mov %0, %%cr0": : "a" (cr3));
  21 }
  22
  23 int map_address(void *physical, void *virtual, int flags)
  24 {
  25         if ((uint32_t) physical & 0xfff || (uint32_t) virtual & 0xfff)
  26                 return ADDRESS_NOT_ALIGNED;
  27
  28         uint32_t pdir_index = (uint32_t) virtual >> 22;
  29         if (pdir_index != 0 && pdir_index != 0x300)
  30                 return INVL_ADDRESS;
  31
  32         uint32_t ptbl_index = ((uint32_t) virtual >> 12) & 0x3ff;
  33         switch (pdir_index) {
  34         case 0:
  35                 if (page_table_firstmb[ptbl_index] & 1 == 1)
  36                         return ADDRESS_ALREADY_MAPPED;
  37                 page_table_firstmb[ptbl_index] = ((uint32_t) physical & ~0xfff) | (flags & 0xfff) | 1;
  38                 break;
  39         case 0x300:
  40                 if (page_table_kernel[ptbl_index] & 1 == 1)
  41                         return ADDRESS_ALREADY_MAPPED;
  42                 page_table_kernel[ptbl_index] = ((uint32_t) physical & ~0xfff) | (flags & 0xfff) | 1;
  43         }
  44
  45         return 0;
  46 }
  47
  48 int map_range(void *phys_start, void *phys_end, void *virt_start, void *virt_end, int flags)
  49 {
  50         if ((uint32_t) phys_start & 0xfff || (uint32_t) phys_end & 0xfff ||
  51                         (uint32_t) virt_start & 0xfff || (uint32_t) virt_end & 0xfff)
  52                 return ADDRESS_NOT_ALIGNED;
  53
  54         if ((uint32_t) phys_end - (uint32_t) phys_start != (uint32_t) virt_end - (uint32_t) virt_start)
  55                 return ADDRESS_RANGE_MISMATCHED;
  56
  57         int loops = ((uint32_t) phys_end - (uint32_t) phys_start) / 4096;
  58         for (int i=0; i<loops; i++) {
  59                 int ret = map_address(phys_start + i*4096, virt_start + i*4096, flags);
  60                 if (ret)
  61                         return ret;
  62         }
  63         return 0;
  64 }
  65
  66 void set_up_page_directory()
  67 {
  68         page_directory[0] = (uint32_t) page_table_firstmb | 3;
  69         page_directory[0x300] = (uint32_t) page_table_kernel | 3;
  70 }