diff --git a/defs.h b/defs.h
index d6d68ad..2bf5005 100644
--- a/defs.h
+++ b/defs.h
@@ -155,23 +155,22 @@ void uartputc(int);
// vm.c
#define PGROUNDUP(sz) ((sz+PGSIZE-1) & ~(PGSIZE-1))
+extern pde_t *kpgdir;
void pminit(void);
void ksegment(void);
void kvmalloc(void);
-void loadkvm(void);
void vminit(void);
void jkstack();
void printstack(void);
-void printpgdir(uint*);
-uint* setupkvm(void); // XXX need pde_t*
-char* uva2ka(uint*, char*);
-int allocuvm(uint*, char*, uint); // XXX need pde_t*
-void freevm(uint*);
-void inituvm(uint*, char*, char*, uint);
-int loaduvm(uint*, char*, struct inode *ip, uint, uint);
-uint* copyuvm(uint*,uint);
+void printpgdir(pde_t *);
+pde_t* setupkvm(void);
+char* uva2ka(pde_t*, char*);
+int allocuvm(pde_t*, char*, uint);
+void freevm(pde_t*);
+void inituvm(pde_t*, char*, char*, uint);
+int loaduvm(pde_t*, char*, struct inode *ip, uint, uint);
+pde_t* copyuvm(pde_t*,uint);
void loadvm(struct proc*);
// number of elements in fixed-size array
#define NELEM(x) (sizeof(x)/sizeof((x)[0]))
-
diff --git a/mmu.h b/mmu.h
index 76d5ce7..378ae22 100644
--- a/mmu.h
+++ b/mmu.h
@@ -148,7 +148,6 @@ struct segdesc {
#define PTE_ADDR(pte) ((uint) (pte) & ~0xFFF)
typedef uint pte_t;
-typedef uint pde_t;
// Control Register flags
#define CR0_PE 0x00000001 // Protection Enable
diff --git a/proc.c b/proc.c
index 3e28200..c1faec6 100644
--- a/proc.c
+++ b/proc.c
@@ -242,7 +242,7 @@ sched(void)
panic("sched running");
if(readeflags()&FL_IF)
panic("sched interruptible");
- loadkvm(); // Switch to the kernel page table
+ lcr3(PADDR(kpgdir)); // Switch to the kernel page table
intena = cpu->intena;
swtch(&proc->context, cpu->scheduler);
cpu->intena = intena;
diff --git a/types.h b/types.h
index 1c19789..e4adf64 100644
--- a/types.h
+++ b/types.h
@@ -1,3 +1,4 @@
typedef unsigned int uint;
typedef unsigned short ushort;
typedef unsigned char uchar;
+typedef uint pde_t;
diff --git a/vm.c b/vm.c
index f24d510..8064ca2 100644
--- a/vm.c
+++ b/vm.c
@@ -6,13 +6,33 @@
#include "proc.h"
#include "elf.h"
-static uint kerntext; // linear/physical address of start of kernel text
-static uint kerntsz;
+// The mappings from logical to linear are one to one (i.e.,
+// segmentation doesn't do anything).
+// The mapping from linear to physical are one to one for the kernel.
+// The mappings for the kernel include all of physical memory (until
+// PHYSTOP), including the I/O hole, and the top of physical address
+// space, where additional devices are located.
+// The kernel itself is linked to be at 1MB, and its physical memory
+// is also at 1MB.
+// Physical memory for user programs is allocated from physical memory
+// between kernend and the end of physical memory (PHYSTOP).
+// The virtual address space of each user program includes the kernel
+// (which is inaccessible in user mode). The user program addresses
+// range from 0 till 640KB (USERTOP), which where the I/O hole starts
+// (both in physical memory and in the kernel's virtual address
+// space).
+
+#define PHYSTOP 0x300000
+#define USERTOP 0xA0000
+
+static uint kerntext; // Linker start kernel at 1MB
+static uint kerntsz;
static uint kerndata;
static uint kerndsz;
static uint kernend;
static uint freesz;
-static pde_t *kpgdir;
+
+pde_t *kpgdir; // One kernel page table for scheduler procs
void
printstack()
@@ -140,13 +160,14 @@ loadvm(struct proc *p)
lcr3(PADDR(p->pgdir)); // switch to new address space
popcli();
- // Conservatively flush other processor's TLBs (XXX lazy--just 2 cpus)
+ // Conservatively flush other processor's TLBs
+ // XXX lazy--just 2 cpus, but xv6 doesn't need shootdown anyway.
if (cpu->id == 0) lapic_tlbflush(1);
else lapic_tlbflush(0);
}
-// Setup kernel part of page table. Linear adresses map one-to-one on
-// physical addresses.
+// Setup kernel part of a page table. Linear adresses map one-to-one
+// on physical addresses.
pde_t*
setupkvm(void)
{
@@ -157,7 +178,7 @@ setupkvm(void)
return 0;
memset(pgdir, 0, PGSIZE);
// Map IO space from 640K to 1Mbyte
- if (!mappages(pgdir, (void *)0xA0000, 0x60000, 0xA0000, PTE_W, 0))
+ if (!mappages(pgdir, (void *)USERTOP, 0x60000, USERTOP, PTE_W, 0))
return 0;
// Map kernel text from kern text addr read-only
if (!mappages(pgdir, (void *) kerntext, kerntsz, kerntext, 0, 0))
@@ -190,7 +211,7 @@ allocuvm(pde_t *pgdir, char *addr, uint sz)
char *mem;
n = PGROUNDUP(sz);
- if (addr + n >= 0xA0000)
+ if (addr + n >= USERTOP)
return 0;
for (i = 0; i < n; i += PGSIZE) {
if (!(mem = kalloc(PGSIZE))) { // XXX cleanup what we did?
@@ -217,7 +238,7 @@ freevm(pde_t *pgdir)
if (pgtab[j] != 0) {
uint pa = PTE_ADDR(pgtab[j]);
uint va = PGADDR(i, j, 0);
- if (va >= 0xA0000) // done with user part?
+ if (va >= USERTOP) // done with user part?
break;
kfree((void *) pa, PGSIZE);
pgtab[j] = 0;
@@ -305,12 +326,12 @@ pminit(void)
kerndata = ph[1].va;
kerntsz = kerndata - kerntext;
kerndsz = kernend - kerndata;
- freesz = 0x300000 - kernend; // XXX no more than 3 Mbyte of phys mem
+ freesz = PHYSTOP - kernend;
cprintf("kerntext@0x%x(sz=0x%x), kerndata@0x%x(sz=0x%x), kernend 0x%x freesz = 0x%x\n",
kerntext, kerntsz, kerndata, kerndsz, kernend, freesz);
- kinit((char *)kernend, freesz); // XXX should be called once on bootcpu
+ kinit((char *)kernend, freesz);
}
// Jump to mainc on a properly-allocated kernel stack
@@ -331,20 +352,13 @@ kvmalloc(void)
kpgdir = setupkvm();
}
-// Switch to the kernel page table (used by the scheduler)
-void
-loadkvm(void)
-{
- lcr3(PADDR(kpgdir));
-}
-
+// Turn on paging.
void
vminit(void)
{
uint cr0;
- loadkvm();
- // Turn on paging.
+ lcr3(PADDR(kpgdir));
cr0 = rcr0();
cr0 |= CR0_PE|CR0_PG|CR0_AM|CR0_WP|CR0_NE|CR0_TS|CR0_EM|CR0_MP;
cr0 &= ~(CR0_TS|CR0_EM);