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 //      dprintf("alloc_pagetable returning %p\n", table);
  48
  49         return table;
  50 }
  51
  52 // allocate enough page tables to allow mapping of kernel and identity mapping of user space
  53 //
  54 // kernel maps at 0xffffffff00000000 (top of 64bit - 4GB)
  55 int mmu_init(kernel_args *ka)
  56 {
  57         ka->arch_args.num_pgtables = 0;
  58
  59         // allocate a new top level pgdir
  60         pgtable0 = alloc_pagetable(ka);
  61         ka->arch_args.phys_pgdir = (addr_t)pgtable0;
  62
  63         // set up the identity map of low ram
  64         setup_identity_map();
  65
  66         dprintf("switching page dirs: new one at %p\n", pgtable0);
  67
  68         // switch to the new pgdir
  69         asm("mov %0, %%rax;"
  70                 "mov %%rax, %%cr3;" :: "m" (pgtable0) : "rax");
  71
  72         dprintf("done switching page dirs\n");
  73
  74         return 0;
  75 }
  76
  77 #define PGTABLE0_ENTRY(vaddr) (((vaddr) >> 39) & 0x1ff)
  78 #define PGTABLE1_ENTRY(vaddr) (((vaddr) >> 30) & 0x1ff)
  79 #define PGTABLE2_ENTRY(vaddr) (((vaddr) >> 21) & 0x1ff)
  80 #define PGTABLE3_ENTRY(vaddr) (((vaddr) >> 12) & 0x1ff)
  81
  82 #define PGENT_TO_ADDR(ent) ((ent) & 0x7ffffffffffff000UL)
  83 #define PGENT_PRESENT(ent) ((ent) & 0x1)
  84
  85 static unsigned long *lookup_pgtable_entry(addr_t vaddr)
  86 {
  87         vaddr &= ~(PAGE_SIZE-1);
  88
  89 //      dprintf("lookup_pgtable_entry: vaddr = (%d, %d, %d, %d)\n",
  90 //              PGTABLE0_ENTRY(vaddr),
  91 //              PGTABLE1_ENTRY(vaddr),
  92 //              PGTABLE2_ENTRY(vaddr),
  93 //              PGTABLE3_ENTRY(vaddr));
  94
  95         // dive into the kernel page tables, allocating as they come up
  96         unsigned long *pgtable = pgtable0;
  97         unsigned long *ent = &pgtable[PGTABLE0_ENTRY(vaddr)];
  98
  99         if (!PGENT_PRESENT(*ent)) {
 100                 pgtable = alloc_pagetable(ka);
 101                 *ent = (addr_t)pgtable | DEFAULT_PAGE_FLAGS;
 102         } else {
 103 //              dprintf("existing ent 0x%lx\n", *ent);
 104                 pgtable = (unsigned long *)PGENT_TO_ADDR(*ent);
 105         }
 106 //      dprintf("pgtable_addr 0 %p\n", pgtable);
 107
 108         ent = &pgtable[PGTABLE1_ENTRY(vaddr)];
 109         if (!PGENT_PRESENT(*ent)) {
 110                 pgtable = alloc_pagetable(ka);
 111                 *ent = (addr_t)pgtable | DEFAULT_PAGE_FLAGS;
 112         } else {
 113 //              dprintf("existing ent 0x%lx\n", *ent);
 114                 pgtable = (unsigned long *)PGENT_TO_ADDR(*ent);
 115         }
 116 //      dprintf("pgtable_addr 1 %p\n", pgtable);
 117
 118         ent = &pgtable[PGTABLE2_ENTRY(vaddr)];
 119         if (!PGENT_PRESENT(*ent)) {
 120                 pgtable = alloc_pagetable(ka);
 121                 *ent = (addr_t)pgtable | DEFAULT_PAGE_FLAGS;
 122         } else {
 123 //              dprintf("existing ent 0x%lx\n", *ent);
 124                 pgtable = (unsigned long *)PGENT_TO_ADDR(*ent);
 125         }
 126 //      dprintf("pgtable_addr 2 %p\n", pgtable);
 127
 128         // now map it
 129
 130         return &pgtable[PGTABLE3_ENTRY(vaddr)];
 131 }
 132
 133 // can only map in kernel space
 134 void mmu_map_page(addr_t vaddr, addr_t paddr)
 135 {
 136 //      dprintf("mmu_map_page: vaddr 0x%lx, paddr 0x%lx\n", vaddr, paddr);
 137
 138         unsigned long *pgtable_entry;
 139
 140         pgtable_entry = lookup_pgtable_entry(vaddr);
 141
 142         paddr &= ~(PAGE_SIZE-1);
 143         *pgtable_entry = paddr | DEFAULT_PAGE_FLAGS;
 144 }
 145