boot/x86/stage3/paging.c

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