Major revisions to documentation.

[pintos-anon] / src / threads / pte.h

diff --git a/src/threads/pte.h b/src/threads/pte.h
new file mode 100644 (file)
index 0000000..74a52f4
--- /dev/null
+++ b/src/threads/pte.h
@@ -0,0 +1,107 @@
+#ifndef THREADS_PTE_H
+#define THREADS_PTE_H
+
+#include "threads/vaddr.h"
+
+/* Functions and macros for working with x86 hardware page
+   tables.
+
+   See vaddr.h for more generic functions and macros for virtual
+   addresses.
+   
+   Virtual addresses are structured as follows:
+
+    31                  22 21                  12 11                   0
+   +----------------------+----------------------+----------------------+
+   | Page Directory Index |   Page Table Index   |    Page Offset       |
+   +----------------------+----------------------+----------------------+
+*/
+
+/* Page table index (bits 12:21). */
+#define        PTSHIFT PGBITS                     /* First page table bit. */
+#define PTBITS  10                         /* Number of page table bits. */
+#define PTSPAN  (1 << PTBITS << PGBITS)    /* Bytes covered by a page table. */
+#define PTMASK  BITMASK(PTSHIFT, PTBITS)   /* Page table bits (12:21). */
+
+/* Page directory index (bits 22:31). */
+#define PDSHIFT (PTSHIFT + PTBITS)         /* First page directory bit. */
+#define PDBITS  10                         /* Number of page dir bits. */
+#define PDMASK  BITMASK(PDSHIFT, PDBITS)   /* Page directory bits (22:31). */
+
+/* Obtains page table index from a virtual address. */
+static inline unsigned pt_no (const void *va) {
+  return ((uintptr_t) va & PTMASK) >> PTSHIFT;
+}
+
+/* Obtains page directory index from a virtual address. */
+static inline uintptr_t pd_no (const void *va) {
+  return (uintptr_t) va >> PDSHIFT;
+}
+
+/* Page directory and page table entries.
+
+   For more information see the section on page tables in the
+   Pintos reference guide chapter, or [IA32-v3a] 3.7.6
+   "Page-Directory and Page-Table Entries".
+
+   PDEs and PTEs share a common format:
+
+   31                                 12 11                     0
+   +------------------------------------+------------------------+
+   |         Physical Address           |         Flags          |
+   +------------------------------------+------------------------+
+
+   In a PDE, the physical address points to a page table.
+   In a PTE, the physical address points to a data or code page.
+   The important flags are listed below.
+   When a PDE or PTE is not "present", the other flags are
+   ignored.
+   A PDE or PTE that is initialized to 0 will be interpreted as
+   "not present", which is just fine. */
+#define PTE_FLAGS 0x00000fff    /* Flag bits. */
+#define PTE_ADDR  0xfffff000    /* Address bits. */
+#define PTE_AVL   0x00000e00    /* Bits available for OS use. */
+#define PTE_P 0x1               /* 1=present, 0=not present. */
+#define PTE_W 0x2               /* 1=read/write, 0=read-only. */
+#define PTE_U 0x4               /* 1=user/kernel, 0=kernel only. */
+#define PTE_A 0x20              /* 1=accessed, 0=not acccessed. */
+#define PTE_D 0x40              /* 1=dirty, 0=not dirty (PTEs only). */
+
+/* Returns a PDE that points to page table PT. */
+static inline uint32_t pde_create (uint32_t *pt) {
+  ASSERT (pg_ofs (pt) == 0);
+  return vtop (pt) | PTE_U | PTE_P | PTE_W;
+}
+
+/* Returns a pointer to the page table that page directory entry
+   PDE, which must "present", points to. */
+static inline uint32_t *pde_get_pt (uint32_t pde) {
+  ASSERT (pde & PTE_P);
+  return ptov (pde & PTE_ADDR);
+}
+
+/* Returns a PTE that points to PAGE.
+   The PTE's page is readable.
+   If WRITABLE is true then it will be writable as well.
+   The page will be usable only by ring 0 code (the kernel). */
+static inline uint32_t pte_create_kernel (uint32_t *page, bool writable) {
+  ASSERT (pg_ofs (page) == 0);
+  return vtop (page) | PTE_P | (writable ? PTE_W : 0);
+}
+
+/* Returns a PTE that points to PAGE.
+   The PTE's page is readable.
+   If WRITABLE is true then it will be writable as well.
+   The page will be usable by both user and kernel code. */
+static inline uint32_t pte_create_user (uint32_t *page, bool writable) {
+  return pte_create_kernel (page, writable) | PTE_U;
+}
+
+/* Returns a pointer to the page that page table entry PTE points
+   to. */
+static inline void *pte_get_page (uint32_t pte) {
+  return ptov (pte & PTE_ADDR);
+}
+
+#endif /* threads/pte.h */
+