kernel/mm/paging.h

   1 /*
   2  *    Copyright (c) 2008 Joshua Phillips. All rights reserved.
   3  *
   4  *  Redistribution and use in source and binary forms, with or without
   5  *  modification, are permitted provided that the following conditions are
   6  *  met:
   7  *
   8  *    1. Redistributions of source code must retain the above copyright
   9  *       notice, this list of conditions and the following disclaimer.
  10  *    2. Redistributions in binary form must reproduce the above copyright
  11  *       notice, this list of conditions and the following disclaimer in
  12  *       the documentation and/or other materials provided with the
  13  *       distribution.
  14  *
  15  *  THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED
  16  *  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  18  *  DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
  19  *  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  20  *  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
  21  *  GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  22  *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
  23  *  IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
  24  *  OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
  25  *  IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26  */
  27
  28 /*
  29  *  This deals with paging (mapping virtual addresses to physical memory)
  30  */
  31
  32 #ifndef MM_PAGING
  33 #define MM_PAGING
  34
  35 #include "stddef.h"
  36 #include "stdint.h"
  37
  38 // Types for page directory entries and
  39 // page table entries (they're almost the same format,
  40 // but it's clearer if we use two different identifiers)
  41 typedef uint32_t pte_t, pde_t;
  42
  43 // page table/directory format
  44 // as defined in the documentation for the CPU
  45 #define PTE_PRESENT (1 << 0)        // page is valid
  46 #define PTE_WRITABLE (1 << 1)       // write access bit
  47 #define PTE_USER (1 << 2)           // user (ring1 - ring3) accessible
  48 #define PTE_WRITE_THROUGH (1 << 3)
  49 #define PTE_CACHE_DISABLED (1 << 4)
  50 #define PTE_ACCESSED (1 << 5)       // set by CPU when page is accessed
  51 #define PTE_DIRTY (1 << 6)          // set by CPU when page is written to
  52 #define PTE_PAT (1 << 7)
  53 #define PTE_GLOBAL (1 << 8)
  54 #define PTE_ADDRESS 0xFFFFF000
  55
  56 #define PDE_PRESENT (1 << 0)
  57 #define PDE_WRITABLE (1 << 1)
  58 #define PDE_USER (1 << 2)
  59 #define PDE_WRITE_THROUGH (1 << 3)
  60 #define PDE_CACHE_DISABLED (1 << 4)
  61 #define PDE_ACCESSED (1 << 5)
  62 #define PDE_PAGESIZE (1 << 7)
  63 #define PDE_GLOBAL (1 << 8)
  64 #define PDE_ADDRESS 0xFFFFF000
  65
  66 // XXX: these values are set here, but if the
  67 // kernel base address changes, these will
  68 // change too!
  69 #define PDE_N 1024        // number of PDEs
  70 #define PDE_N_KERNEL 256  // number of kernel PDEs
  71 #define PDE_N_USER 768    // number of user PDEs
  72 #define PDE_KERNEL_FIRST 768
  73
  74 // Store a data structure mirroring the page directory
  75 // and page tables, but with virtual addresses.
  76 struct vpde {
  77     unsigned unused: 12; // this may be useful
  78     unsigned vaddr : 20; // TODO: vaddr is in kernel address space - save 2 bits or more!
  79 };
  80
  81 struct pagedir {
  82     struct pagedir *prev, *next; // linked list (so we can update all page directories at once)
  83     uintptr_t phys_addr; // physical address of page directory
  84     pde_t *virt_addr; // kernel-virtual address of page directory
  85     struct vpde vpd[768];
  86 };
  87
  88 // functions to get/set cr2 and cr3
  89 // cr2 contains the virtual address of the last page fault.
  90 // cr3 contains the address of the page directory.
  91
  92 static inline uint32_t get_cr2(void)
  93 {
  94     uint32_t old_cr3;
  95     asm volatile ("movl %%cr2,%%eax" : "=a" (old_cr3));
  96     return old_cr3;
  97 }
  98
  99 static inline uint32_t get_cr3(void)
 100 {
 101     uint32_t old_cr3;
 102     asm volatile ("movl %%cr3,%%eax" : "=a" (old_cr3));
 103     return old_cr3;
 104 }
 105
 106 static inline void set_cr3(uint32_t new_cr3)
 107 {
 108     asm volatile ("movl %%eax,%%cr3" :: "a" (new_cr3));
 109 }
 110
 111 // Create the initial page directory structure.
 112 // (The actual page directory will already exist)
 113 void create_init_pagedir(struct pagedir *init_pagedir);
 114
 115 // Create a page directory. The page directory entries for the kernel's
 116 // address space are duplicated.
 117 // Caller is expected to provide storage for the 'struct pagedir'.
 118 // The address of the 'struct pagedir' must not change!
 119 // Returns 0=ok, 1=error (out of memory)
 120 int pagedir_create(struct pagedir *pagedir);
 121
 122 // Destroy a page directory
 123 void pagedir_destroy(struct pagedir *pagedir);
 124
 125 // Return the physical address pointed to by 'virtual'
 126 uintptr_t xlat_v2p(struct pagedir *pd, uintptr_t virtual);
 127
 128 // Alter the current memory map: map a physical region to the
 129 // current virtual address space.
 130 // Flags are PTE_* constants
 131 // Return: 0=ok, 1=error
 132 int map_mem(struct pagedir *pd, uintptr_t physical, uintptr_t virtual, size_t n_pages, int flags);
 133
 134 // Sets up an initial 'struct pagedir' to represent the initial page directory
 135 // (that was created in start.asm)
 136 void paging_init(void);
 137
 138 // Switch to a new page directory. Be careful. Paging is confusing.
 139 void pagedir_switch(struct pagedir *new_pagedir);
 140
 141 #endif