arch/x86/boot/compressed/pagetable.c

   1 /*
   2  * This code is used on x86_64 to create page table identity mappings on
   3  * demand by building up a new set of page tables (or appending to the
   4  * existing ones), and then switching over to them when ready.
   5  */
   6
   7 /*
   8  * Since we're dealing with identity mappings, physical and virtual
   9  * addresses are the same, so override these defines which are ultimately
  10  * used by the headers in misc.h.
  11  */
  12 #define __pa(x)  ((unsigned long)(x))
  13 #define __va(x)  ((void *)((unsigned long)(x)))
  14
  15 #include "misc.h"
  16
  17 /* These actually do the work of building the kernel identity maps. */
  18 #include <asm/init.h>
  19 #include <asm/pgtable.h>
  20 #include "../../mm/ident_map.c"
  21
  22 /* Used by pgtable.h asm code to force instruction serialization. */
  23 unsigned long __force_order;
  24
  25 /* Used to track our page table allocation area. */
  26 struct alloc_pgt_data {
  27         unsigned char *pgt_buf;
  28         unsigned long pgt_buf_size;
  29         unsigned long pgt_buf_offset;
  30 };
  31
  32 /*
  33  * Allocates space for a page table entry, using struct alloc_pgt_data
  34  * above. Besides the local callers, this is used as the allocation
  35  * callback in mapping_info below.
  36  */
  37 static void *alloc_pgt_page(void *context)
  38 {
  39         struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
  40         unsigned char *entry;
  41
  42         /* Validate there is space available for a new page. */
  43         if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
  44                 debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
  45                 debug_putaddr(pages->pgt_buf_offset);
  46                 debug_putaddr(pages->pgt_buf_size);
  47                 return NULL;
  48         }
  49
  50         entry = pages->pgt_buf + pages->pgt_buf_offset;
  51         pages->pgt_buf_offset += PAGE_SIZE;
  52
  53         return entry;
  54 }
  55
  56 /* Used to track our allocated page tables. */
  57 static struct alloc_pgt_data pgt_data;
  58
  59 /* The top level page table entry pointer. */
  60 static unsigned long level4p;
  61
  62 /* Locates and clears a region for a new top level page table. */
  63 static void prepare_level4(void)
  64 {
  65         /*
  66          * It should be impossible for this not to already be true,
  67          * but since calling this a second time would rewind the other
  68          * counters, let's just make sure this is reset too.
  69          */
  70         pgt_data.pgt_buf_offset = 0;
  71
  72         /*
  73          * If we came here via startup_32(), cr3 will be _pgtable already
  74          * and we must append to the existing area instead of entirely
  75          * overwriting it.
  76          */
  77         level4p = read_cr3();
  78         if (level4p == (unsigned long)_pgtable) {
  79                 debug_putstr("booted via startup_32()\n");
  80                 pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
  81                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
  82                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
  83         } else {
  84                 debug_putstr("booted via startup_64()\n");
  85                 pgt_data.pgt_buf = _pgtable;
  86                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
  87                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
  88                 level4p = (unsigned long)alloc_pgt_page(&pgt_data);
  89         }
  90 }
  91
  92 /*
  93  * Adds the specified range to what will become the new identity mappings.
  94  * Once all ranges have been added, the new mapping is activated by calling
  95  * finalize_identity_maps() below.
  96  */
  97 void add_identity_map(unsigned long start, unsigned long size)
  98 {
  99         struct x86_mapping_info mapping_info = {
 100                 .alloc_pgt_page = alloc_pgt_page,
 101                 .context        = &pgt_data,
 102                 .pmd_flag       = __PAGE_KERNEL_LARGE_EXEC,
 103         };
 104         unsigned long end = start + size;
 105
 106         /* Make sure we have a top level page table ready to use. */
 107         if (!level4p)
 108                 prepare_level4();
 109
 110         /* Align boundary to 2M. */
 111         start = round_down(start, PMD_SIZE);
 112         end = round_up(end, PMD_SIZE);
 113         if (start >= end)
 114                 return;
 115
 116         /* Build the mapping. */
 117         kernel_ident_mapping_init(&mapping_info, (pgd_t *)level4p,
 118                                   start, end);
 119 }
 120
 121 /*
 122  * This switches the page tables to the new level4 that has been built
 123  * via calls to add_identity_map() above. If booted via startup_32(),
 124  * this is effectively a no-op.
 125  */
 126 void finalize_identity_maps(void)
 127 {
 128         write_cr3(level4p);
 129 }