sanchayanmaity/xv6-cs450
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2011
This commit is contained in:
Frans Kaashoek 2011-08-15 20:21:14 -04:00
parent a4b213cf49
commit d9818bdd7d
2 changed files with 13 additions and 13 deletions
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2
README
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@ -26,7 +26,7 @@ In addition, we are grateful for the patches contributed by Greg
Price, Yandong Mao, and Hitoshi Mitake.
The code in the files that constitute xv6 is
Copyright 2006-2007 Frans Kaashoek, Robert Morris, and Russ Cox.
Copyright 2006-2011 Frans Kaashoek, Robert Morris, and Russ Cox.
ERROR REPORTS

24
vm.c
View file

@ -18,7 +18,7 @@ seginit(void)
{
struct cpu *c;
// Map virtual addresses to linear addresses using identity map.
// Map "logical" addresses to virtual addresses using identity map.
// Cannot share a CODE descriptor for both kernel and user
// because it would have to have DPL_USR, but the CPU forbids
// an interrupt from CPL=0 to DPL=3.
@ -40,7 +40,7 @@ seginit(void)
}
// Return the address of the PTE in page table pgdir
// that corresponds to linear address va. If alloc!=0,
// that corresponds to virtual address va. If alloc!=0,
// create any required page table pages.
static pte_t *
walkpgdir(pde_t *pgdir, const void *va, char* (*alloc)(void))
@ -64,17 +64,17 @@ walkpgdir(pde_t *pgdir, const void *va, char* (*alloc)(void))
return &pgtab[PTX(va)];
}
// Create PTEs for linear addresses starting at la that refer to
// Create PTEs for virtual addresses starting at la that refer to
// physical addresses starting at pa. la and size might not
// be page-aligned.
static int
mappages(pde_t *pgdir, void *la, uint size, uint pa, int perm, char* (*alloc)(void))
mappages(pde_t *pgdir, void *va, uint size, uint pa, int perm, char* (*alloc)(void))
{
char *a, *last;
pte_t *pte;
a = PGROUNDDOWN(la);
last = PGROUNDDOWN(la + size - 1);
a = PGROUNDDOWN(va);
last = PGROUNDDOWN(va + size - 1);
for(;;){
pte = walkpgdir(pgdir, a, alloc);
if(pte == 0)
@ -90,7 +90,7 @@ mappages(pde_t *pgdir, void *la, uint size, uint pa, int perm, char* (*alloc)(vo
return 0;
}
// The mappings from logical to linear are one to one (i.e.,
// The mappings from logical to virtual are one to one (i.e.,
// segmentation doesn't do anything).
// There is one page table per process, plus one that's used
// when a CPU is not running any process (kpgdir).
@ -98,7 +98,6 @@ mappages(pde_t *pgdir, void *la, uint size, uint pa, int perm, char* (*alloc)(vo
// page protection bits prevent it from using anything other
// than its memory.
//
//
// setupkvm() and exec() set up every page table like this:
// 0..USERTOP : user memory (text, data, stack, heap), mapped to some unused phys mem
// KERNBASE..KERNBASE+1M: mapped to 0..1M
@ -112,9 +111,9 @@ mappages(pde_t *pgdir, void *la, uint size, uint pa, int perm, char* (*alloc)(vo
// (which is inaccessible in user mode). The user program sits in
// the bottom of the address space, and the kernel at the top at KERNBASE.
static struct kmap {
void *l;
uint p;
uint e;
void *virt;
uint phys_start;
uint phys_end;
int perm;
} kmap[] = {
{ P2V(0), 0, 1024*1024, PTE_W}, // First 1Mbyte contains BIOS and some IO devices
@ -135,7 +134,8 @@ setupkvm(char* (*alloc)(void))
memset(pgdir, 0, PGSIZE);
k = kmap;
for(k = kmap; k < &kmap[NELEM(kmap)]; k++)
if(mappages(pgdir, k->l, k->e - k->p, (uint)k->p, k->perm, alloc) < 0)
if(mappages(pgdir, k->virt, k->phys_end - k->phys_start, (uint)k->phys_start,
k->perm, alloc) < 0)
return 0;
return pgdir;