Improve comments.

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

diff --git a/src/threads/mmu.h b/src/threads/mmu.h
index 64d82daa8e9b82098ef14bf4b9f56fe7b34c688d..9f71d4a3a9d2b970264371eceb310da098a25d6c 100644 (file)
--- a/src/threads/mmu.h
+++ b/src/threads/mmu.h
@@ -9,24 +9,24 @@
 
 /* Virtual to physical translation works like this on an x86:
 
-   - The top 10 bits of the virtual address (bits 22:32) are used
+   - The top 10 bits of the virtual address (bits 22:31) are used
      to index into the page directory.  If the PDE is marked
      "present," the physical address of a page table is read from
      the PDE thus obtained.  If the PDE is marked "not present"
      then a page fault occurs.
 
-   - The next 10 bits of the virtual address (bits 12:22) are
+   - The next 10 bits of the virtual address (bits 12:21) are
      used to index into the page table.  If the PTE is marked
      "present," the physical address of a data page is read from
      the PTE thus obtained.  If the PTE is marked "not present"
      then a page fault occurs.
 
-   - The bottom 12 bits of the virtual address (bits 0:12) are
+   - The bottom 12 bits of the virtual address (bits 0:11) are
      added to the data page's physical base address, producing
      the final physical address.
 
 
-   32                    22                     12                      0
+    31                  22 21                  12 11                   0
    +--------------------------------------------------------------------+
    | Page Directory Index |   Page Table Index   |    Page Offset       |
    +--------------------------------------------------------------------+
@@ -106,6 +106,20 @@ static inline void *pg_round_down (const void *va) {
    virtual address space belongs to the kernel. */
 #define        PHYS_BASE ((void *) LOADER_PHYS_BASE)
 
+/* Returns true if VADDR is a user virtual address. */
+static inline bool
+is_user_vaddr (const void *vaddr) 
+{
+  return vaddr < PHYS_BASE;
+}
+
+/* Returns true if VADDR is a kernel virtual address. */
+static inline bool
+is_kernel_vaddr (const void *vaddr) 
+{
+  return vaddr >= PHYS_BASE;
+}
+
 /* Returns kernel virtual address at which physical address PADDR
    is mapped. */
 static inline void *
@@ -121,18 +135,19 @@ ptov (uintptr_t paddr)
 static inline uintptr_t
 vtop (const void *vaddr)
 {
-  ASSERT (vaddr >= PHYS_BASE);
+  ASSERT (is_kernel_vaddr (vaddr));
 
   return (uintptr_t) vaddr - (uintptr_t) PHYS_BASE;
 }
 \f
 /* Page directories and page tables.
 
-   For more information see [IA32-v3] pages 3-23 to 3-28.
+   For more information see [IA32-v3a] 3.7.6 "Page-Directory and
+   Page-Table Entries".
 
    PDEs and PTEs share a common format:
 
-   32                                   12                       0
+   31                                 12 11                     0
    +------------------------------------+------------------------+
    |         Physical Address           |         Flags          |
    +------------------------------------+------------------------+
@@ -169,7 +184,7 @@ static inline uint32_t *pde_get_pt (uint32_t pde) {
 }
 
 /* Obtains page table index from a virtual address. */
-static inline unsigned pt_no (void *va) {
+static inline unsigned pt_no (const void *va) {
   return ((uintptr_t) va & PTMASK) >> PTSHIFT;
 }
 
@@ -190,10 +205,9 @@ static inline uint32_t pte_create_user (uint32_t *page, bool writable) {
   return pte_create_kernel (page, writable) | PG_U;
 }
 
-/* Returns a pointer to the page that page table entry PTE, which
-   must "present", points to. */
+/* Returns a pointer to the page that page table entry PTE points
+   to. */
 static inline void *pte_get_page (uint32_t pte) {
-  ASSERT (pte & PG_P);
   return ptov (pte & ~PGMASK);
 }