/* Virtual to physical translation works like this on an x86:
- - The top 10 bits of the virtual address (bits 22:31) are used
+ - The top 10 bits of the virtual address (bits 22:32) 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 12:21) are
+ - The next 10 bits of the virtual address (bits 12:22) 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 0:11) are
+ - The bottom 12 bits of the virtual address (bits 0:12) are
added to the data page's physical base address, producing
the final physical address.
#define MASK(SHIFT, CNT) (((1ul << (CNT)) - 1) << (SHIFT))
-/* Page offset (bits 0:11). */
-#define PGSHIFT 0 /* First offset bit. */
-#define PGBITS 12 /* Number of offset bits. */
-#define PGMASK MASK(PGSHIFT, PGBITS)
-#define PGSIZE (1 << PGBITS)
+/* Page offset (bits 0:12). */
+#define PGSHIFT 0 /* Index of first offset bit. */
+#define PGBITS 12 /* Number of offset bits. */
+#define PGMASK MASK(PGSHIFT, PGBITS) /* Page offset bits (0:12). */
+#define PGSIZE (1 << PGBITS) /* Bytes in a page. */
-/* Page table (bits 12:21). */
-#define PTSHIFT PGBITS /* First page table bit. */
-#define PTBITS 10 /* Number of page table bits. */
-#define PTMASK MASK(PTSHIFT, PTBITS)
+/* Page table (bits 12:22). */
+#define PTSHIFT PGBITS /* Index of first page table bit. */
+#define PTBITS 10 /* Number of page table bits. */
+#define PTMASK MASK(PTSHIFT, PTBITS) /* Page table bits (12:22). */
+#define PTSPAN (1 << PTBITS << PGBITS) /* Bytes covered by a page table. */
-/* Page directory (bits 22:31). */
-#define PDSHIFT (PTSHIFT + PTBITS) /* First page dir bit. */
-#define PDBITS 10 /* Number of page dir bits. */
-#define PDMASK MASK(PDSHIFT, PDBITS)
+/* Page directory (bits 22:32). */
+#define PDSHIFT (PTSHIFT + PTBITS) /* First page dir bit. */
+#define PDBITS 10 /* Number of page dir bits. */
+#define PDMASK MASK(PDSHIFT, PDBITS) /* Page directory bits (22:32). */
/* Offset within a page. */
-static inline unsigned pg_ofs (void *va) { return (uintptr_t) va & PGMASK; }
+static inline unsigned pg_ofs (const void *va) {
+ return (uintptr_t) va & PGMASK;
+}
/* Virtual page number. */
-static inline uintptr_t pg_no (void *va) { return (uintptr_t) va >> PTSHIFT; }
+static inline uintptr_t pg_no (const void *va) {
+ return (uintptr_t) va >> PTSHIFT;
+}
/* Round up to nearest page boundary. */
-static inline void *pg_round_up (void *va) {
+static inline void *pg_round_up (const void *va) {
return (void *) (((uintptr_t) va + PGSIZE - 1) & ~PGMASK);
}
/* Round down to nearest page boundary. */
-static inline void *pg_round_down (void *va) {
+static inline void *pg_round_down (const void *va) {
return (void *) ((uintptr_t) va & ~PGMASK);
}
+/* Base address of the 1:1 physical-to-virtual mapping. Physical
+ memory is mapped starting at this virtual address. Thus,
+ physical address 0 is accessible at PHYS_BASE, physical
+ address address 0x1234 at (uint8_t *) PHYS_BASE + 0x1234, and
+ so on.
+
+ This address also marks the end of user programs' address
+ space. Up to this point in memory, user programs are allowed
+ to map whatever they like. At this point and above, the
+ virtual address space belongs to the kernel. */
#define PHYS_BASE ((void *) LOADER_PHYS_BASE)
/* Returns kernel virtual address at which physical address PADDR
/* Returns physical address at which kernel virtual address VADDR
is mapped. */
static inline uintptr_t
-vtop (void *vaddr)
+vtop (const void *vaddr)
{
ASSERT (vaddr >= PHYS_BASE);
#define PG_D 0x40 /* 1=dirty, 0=not dirty (PTEs only). */
/* Obtains page directory index from a virtual address. */
-static inline uintptr_t pd_no (void *va) { return (uintptr_t) va >> PDSHIFT; }
+static inline uintptr_t pd_no (const void *va) {
+ return (uintptr_t) va >> PDSHIFT;
+}
/* Returns a PDE that points to page table PT. */
static inline uint32_t pde_create (uint32_t *pt) {