boot/pc/x86_64/mmu.c

   1 /*
   2 ** Copyright 2008, Travis Geiselbrecht. All rights reserved.
   3 ** Distributed under the terms of the NewOS License.
   4 */
   5 #include <string.h>
   6 #include "stage2_priv.h"
   7
   8 // working pagedir and pagetables
   9 static unsigned long *pgtable0 = 0;
  10
  11 static unsigned long *pgtables_user = 0;
  12
  13 static void setup_identity_map(void)
  14 {
  15         // build a set of page tables to keep the low identity map
  16         // the kernel will blow this away shortly
  17         pgtables_user = (unsigned long *)0x11000; // use this random spot
  18
  19         // clear out all of these page tables
  20         memset(pgtables_user, 0, PAGE_SIZE * 2);
  21
  22         // point the top level page directory at it
  23         pgtable0[0] = (addr_t)pgtables_user | DEFAULT_PAGE_FLAGS;
  24
  25         // second level table points to the next
  26         pgtables_user[0] = ((addr_t)pgtables_user + PAGE_SIZE) | DEFAULT_PAGE_FLAGS;
  27
  28         // third level page table identity maps 1GB using 2MB pages
  29         int i;
  30         for (i=0; i < 512; i++)
  31                 pgtables_user[512 + i] = (i * 0x200000) | (1<<7) | DEFAULT_PAGE_FLAGS;
  32 }
  33
  34 static unsigned long *alloc_pagetable(kernel_args *ka)
  35 {
  36         int i;
  37         unsigned long *table;
  38
  39         table = (unsigned long *)next_paddr;
  40         next_paddr += PAGE_SIZE;
  41         ka->arch_args.pgtables[ka->arch_args.num_pgtables++] = (addr_t)table;
  42
  43         // clear it out
  44         for(i = 0; i < 512; i++)
  45                 table[i] = 0;
  46
  47         return table;
  48 }
  49
  50 // allocate enough page tables to allow mapping of kernel and identity mapping of user space
  51 //
  52 // kernel maps at 0xffffffff00000000 (top of 64bit - 4GB)
  53 int mmu_init(kernel_args *ka)
  54 {
  55         ka->arch_args.num_pgtables = 0;
  56
  57         // allocate a new top level pgdir
  58         pgtable0 = alloc_pagetable(ka);
  59
  60         // set up the identity map of low ram
  61         setup_identity_map();
  62
  63         dprintf("switching page dirs: new one at %p\n", pgtable0);
  64
  65         // switch to the new pgdir
  66         asm("mov %0, %%rax;"
  67                 "mov %%rax, %%cr3;" :: "m" (pgtable0) : "rax");
  68
  69         dprintf("done switching page dirs\n");
  70
  71         return 0;
  72 }
  73
  74 #define PGTABLE0_ENTRY(vaddr) (((vaddr) >> 39) & 0x1ff)
  75 #define PGTABLE1_ENTRY(vaddr) (((vaddr) >> 30) & 0x1ff)
  76 #define PGTABLE2_ENTRY(vaddr) (((vaddr) >> 21) & 0x1ff)
  77 #define PGTABLE3_ENTRY(vaddr) (((vaddr) >> 12) & 0x1ff)
  78
  79 #define PGENT_TO_ADDR(ent) ((ent) & 0x7ffffffffffff000UL)
  80 #define PGENT_PRESENT(ent) ((ent) & 0x1)
  81
  82 static unsigned long *lookup_pgtable_entry(addr_t vaddr)
  83 {
  84         vaddr &= ~(PAGE_SIZE-1);
  85
  86 //      dprintf("lookup_pgtable_entry: vaddr = (%d, %d, %d, %d)\n",
  87 //              PGTABLE0_ENTRY(vaddr),
  88 //              PGTABLE1_ENTRY(vaddr),
  89 //              PGTABLE2_ENTRY(vaddr),
  90 //              PGTABLE3_ENTRY(vaddr));
  91
  92         // dive into the kernel page tables, allocating as they come up
  93         unsigned long *pgtable = pgtable0;
  94         unsigned long *ent = &pgtable[PGTABLE0_ENTRY(vaddr)];
  95
  96         if (!PGENT_PRESENT(*ent)) {
  97                 pgtable = alloc_pagetable(ka);
  98                 *ent = (addr_t)pgtable | DEFAULT_PAGE_FLAGS;
  99         } else {
 100                 pgtable = (unsigned long *)PGENT_TO_ADDR(*ent);
 101         }
 102 //      dprintf("pgtable_addr 0 %p\n", pgtable);
 103
 104         ent = &pgtable[PGTABLE1_ENTRY(vaddr)];
 105         if (!PGENT_PRESENT(*ent)) {
 106                 pgtable = alloc_pagetable(ka);
 107                 *ent = (addr_t)pgtable | DEFAULT_PAGE_FLAGS;
 108         } else {
 109                 pgtable = (unsigned long *)PGENT_TO_ADDR(*ent);
 110         }
 111 //      dprintf("pgtable_addr 1 %p\n", pgtable);
 112
 113         ent = &pgtable[PGTABLE2_ENTRY(vaddr)];
 114         if (!PGENT_PRESENT(*ent)) {
 115                 pgtable = alloc_pagetable(ka);
 116                 *ent = (addr_t)pgtable | DEFAULT_PAGE_FLAGS;
 117         } else {
 118                 pgtable = (unsigned long *)PGENT_TO_ADDR(*ent);
 119         }
 120 //      dprintf("pgtable_addr 2 %p\n", pgtable);
 121
 122         // now map it
 123
 124         return &pgtable[PGTABLE3_ENTRY(vaddr)];
 125 }
 126
 127 // can only map in kernel space
 128 void mmu_map_page(addr_t vaddr, addr_t paddr)
 129 {
 130 //      dprintf("mmu_map_page: vaddr 0x%lx, paddr 0x%lx\n", vaddr, paddr);
 131
 132         unsigned long *pgtable_entry;
 133
 134         pgtable_entry = lookup_pgtable_entry(vaddr);
 135
 136         paddr &= ~(PAGE_SIZE-1);
 137         *pgtable_entry = paddr | DEFAULT_PAGE_FLAGS;
 138 }
 139