Initial version of single-cpu xv6 with page tables

1 files changed, 88 insertions, 0 deletions

diff --git a/mmu.h b/mmu.h
index 364d05b..76d5ce7 100644
--- a/mmu.h
+++ b/mmu.h
@@ -62,6 +62,8 @@ struct segdesc {
 #define STA_R       0x2     // Readable (executable segments)
 #define STA_A       0x1     // Accessed
 
+// 
+
 // System segment type bits
 #define STS_T16A    0x1     // Available 16-bit TSS
 #define STS_LDT     0x2     // Local Descriptor Table
@@ -76,6 +78,92 @@ struct segdesc {
 #define STS_IG32    0xE     // 32-bit Interrupt Gate
 #define STS_TG32    0xF     // 32-bit Trap Gate
 
+
+// A linear address 'la' has a three-part structure as follows:
+//
+// +--------10------+-------10-------+---------12----------+
+// | Page Directory |   Page Table   | Offset within Page  |
+// |      Index     |      Index     |                     |
+// +----------------+----------------+---------------------+
+//  \--- PDX(la) --/ \--- PTX(la) --/ \---- PGOFF(la) ----/
+//  \----------- PPN(la) -----------/
+//
+// The PDX, PTX, PGOFF, and PPN macros decompose linear addresses as shown.
+// To construct a linear address la from PDX(la), PTX(la), and PGOFF(la),
+// use PGADDR(PDX(la), PTX(la), PGOFF(la)).
+
+// page number field of address
+#define PPN(la)		(((uint) (la)) >> PTXSHIFT)
+#define VPN(la)		PPN(la)		// used to index into vpt[]
+
+// page directory index
+#define PDX(la)		((((uint) (la)) >> PDXSHIFT) & 0x3FF)
+#define VPD(la)		PDX(la)		// used to index into vpd[]
+
+// page table index
+#define PTX(la)		((((uint) (la)) >> PTXSHIFT) & 0x3FF)
+
+// offset in page
+#define PGOFF(la)	(((uint) (la)) & 0xFFF)
+
+// construct linear address from indexes and offset
+#define PGADDR(d, t, o)	((uint) ((d) << PDXSHIFT | (t) << PTXSHIFT | (o)))
+
+// mapping from physical addresses to virtual addresses is the identity one
+// (really linear addresses, but we map linear to physical also directly)
+#define PADDR(a)       ((uint) a)
+
+// Page directory and page table constants.
+#define NPDENTRIES	1024		// page directory entries per page directory
+#define NPTENTRIES	1024		// page table entries per page table
+
+#define PGSIZE		4096		// bytes mapped by a page
+#define PGSHIFT		12		// log2(PGSIZE)
+
+#define PTSIZE		(PGSIZE*NPTENTRIES) // bytes mapped by a page directory entry
+#define PTSHIFT		22		// log2(PTSIZE)
+
+#define PTXSHIFT	12		// offset of PTX in a linear address
+#define PDXSHIFT	22		// offset of PDX in a linear address
+
+// Page table/directory entry flags.
+#define PTE_P		0x001	// Present
+#define PTE_W		0x002	// Writeable
+#define PTE_U		0x004	// User
+#define PTE_PWT		0x008	// Write-Through
+#define PTE_PCD		0x010	// Cache-Disable
+#define PTE_A		0x020	// Accessed
+#define PTE_D		0x040	// Dirty
+#define PTE_PS		0x080	// Page Size
+#define PTE_MBZ		0x180	// Bits must be zero
+
+// The PTE_AVAIL bits aren't used by the kernel or interpreted by the
+// hardware, so user processes are allowed to set them arbitrarily.
+#define PTE_AVAIL	0xE00	// Available for software use
+
+// Only flags in PTE_USER may be used in system calls.
+#define PTE_USER	(PTE_AVAIL | PTE_P | PTE_W | PTE_U)
+
+// Address in page table or page directory entry
+#define PTE_ADDR(pte)	((uint) (pte) & ~0xFFF)
+
+typedef uint pte_t;
+typedef uint pde_t;
+
+// Control Register flags
+#define CR0_PE		0x00000001	// Protection Enable
+#define CR0_MP		0x00000002	// Monitor coProcessor
+#define CR0_EM		0x00000004	// Emulation
+#define CR0_TS		0x00000008	// Task Switched
+#define CR0_ET		0x00000010	// Extension Type
+#define CR0_NE		0x00000020	// Numeric Errror
+#define CR0_WP		0x00010000	// Write Protect
+#define CR0_AM		0x00040000	// Alignment Mask
+#define CR0_NW		0x20000000	// Not Writethrough
+#define CR0_CD		0x40000000	// Cache Disable
+#define CR0_PG		0x80000000	// Paging
+
+
 // PAGEBREAK: 40
 // Task state segment format
 struct taskstate {