xv6/vm.c

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#include "param.h"
#include "types.h"
#include "defs.h"
#include "x86.h"
#include "mmu.h"
#include "proc.h"
#include "elf.h"
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// 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
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static uint kerntext; // Linker starts kernel at 1MB
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static uint kerntsz;
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static uint kerndata;
static uint kerndsz;
static uint kernend;
static uint freesz;
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pde_t *kpgdir; // One kernel page table for scheduler procs
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void
printpgdir(pde_t *pgdir)
{
uint i;
uint j;
cprintf("printpgdir 0x%x\n", pgdir);
for (i = 0; i < NPDENTRIES; i++) {
if (pgdir[i] != 0 && i < 100) {
cprintf("pgdir %d, v=0x%x\n", i, pgdir[i]);
pte_t *pgtab = (pte_t*) PTE_ADDR(pgdir[i]);
for (j = 0; j < NPTENTRIES; j++) {
if (pgtab[j] != 0)
cprintf("pgtab %d, v=0x%x, addr=0x%x\n", j, PGADDR(i, j, 0),
PTE_ADDR(pgtab[j]));
}
}
}
cprintf("printpgdir done\n", pgdir);
}
// return the address of the PTE in page table pgdir
// that corresponds to linear address va. if create!=0,
// create any required page table pages.
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static pte_t *
walkpgdir(pde_t *pgdir, const void *va, int create)
{
uint r;
pde_t *pde;
pte_t *pgtab;
pde = &pgdir[PDX(va)];
if (*pde & PTE_P) {
pgtab = (pte_t*) PTE_ADDR(*pde);
} else if (!create || !(r = (uint) kalloc(PGSIZE)))
return 0;
else {
pgtab = (pte_t*) r;
// Make sure all those PTE_P bits are zero.
memset(pgtab, 0, PGSIZE);
// The permissions here are overly generous, but they can
// be further restricted by the permissions in the page table
// entries, if necessary.
*pde = PADDR(r) | PTE_P | PTE_W | PTE_U;
}
return &pgtab[PTX(va)];
}
// create PTEs for linear addresses starting at la that refer to
// physical addresses starting at pa.
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static int
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mappages(pde_t *pgdir, void *la, uint size, uint pa, int perm)
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{
uint i;
pte_t *pte;
for (i = 0; i < size; i += PGSIZE) {
if (!(pte = walkpgdir(pgdir, (void*)(la + i), 1)))
return 0;
if(*pte & PTE_P)
panic("remap");
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*pte = (pa + i) | perm | PTE_P;
}
return 1;
}
// Set up CPU's kernel segment descriptors.
// Run once at boot time on each CPU.
void
ksegment(void)
{
struct cpu *c;
// Map once virtual addresses to linear addresses using identity map
c = &cpus[cpunum()];
c->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, 0);
c->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, 0x0, 0xffffffff, DPL_USER);
c->gdt[SEG_UDATA] = SEG(STA_W, 0x0, 0xffffffff, DPL_USER);
// map cpu, and curproc
c->gdt[SEG_KCPU] = SEG(STA_W, &c->cpu, 8, 0);
lgdt(c->gdt, sizeof(c->gdt));
loadgs(SEG_KCPU << 3);
// Initialize cpu-local storage.
cpu = c;
proc = 0;
}
// Setup address space and current process task state.
void
loadvm(struct proc *p)
{
pushcli();
// Setup TSS
cpu->gdt[SEG_TSS] = SEG16(STS_T32A, &cpu->ts, sizeof(cpu->ts)-1, 0);
cpu->gdt[SEG_TSS].s = 0;
cpu->ts.ss0 = SEG_KDATA << 3;
cpu->ts.esp0 = (uint)proc->kstack + KSTACKSIZE;
ltr(SEG_TSS << 3);
if (p->pgdir == 0)
panic("loadvm: no pgdir\n");
lcr3(PADDR(p->pgdir)); // switch to new address space
popcli();
}
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// Setup kernel part of a page table. Linear adresses map one-to-one
// on physical addresses.
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pde_t*
setupkvm(void)
{
pde_t *pgdir;
// Allocate page directory
if (!(pgdir = (pde_t *) kalloc(PGSIZE)))
return 0;
memset(pgdir, 0, PGSIZE);
// Map IO space from 640K to 1Mbyte
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if (!mappages(pgdir, (void *)USERTOP, 0x60000, USERTOP, PTE_W))
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return 0;
// Map kernel text from kern text addr read-only
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if (!mappages(pgdir, (void *) kerntext, kerntsz, kerntext, 0))
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return 0;
// Map kernel data form kern data addr R/W
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if (!mappages(pgdir, (void *) kerndata, kerndsz, kerndata, PTE_W))
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return 0;
// Map dynamically-allocated memory read/write (kernel stacks, user mem)
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if (!mappages(pgdir, (void *) kernend, freesz, PADDR(kernend), PTE_W))
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return 0;
// Map devices such as ioapic, lapic, ...
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if (!mappages(pgdir, (void *)0xFE000000, 0x2000000, 0xFE000000, PTE_W))
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return 0;
return pgdir;
}
char*
uva2ka(pde_t *pgdir, char *uva)
{
pte_t *pte = walkpgdir(pgdir, uva, 0);
if (pte == 0) return 0;
uint pa = PTE_ADDR(*pte);
return (char *)pa;
}
// allocate sz bytes more memory for a process starting at the
// given user address; allocates physical memory and page
// table entries. addr and sz need not be page-aligned.
// it is a no-op for any parts of the requested memory
// that are already allocated.
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int
allocuvm(pde_t *pgdir, char *addr, uint sz)
{
if (addr + sz >= (char*)USERTOP)
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return 0;
char *start = PGROUNDDOWN(addr);
char *last = PGROUNDDOWN(addr + sz - 1);
char *a;
for(a = start; a <= last; a += PGSIZE){
pte_t *pte = walkpgdir(pgdir, a, 0);
if(pte == 0 || (*pte & PTE_P) == 0){
char *mem = kalloc(PGSIZE);
if(mem == 0){
// XXX clean up?
return 0;
}
memset(mem, 0, PGSIZE);
mappages(pgdir, a, PGSIZE, PADDR(mem), PTE_W|PTE_U);
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}
}
return 1;
}
void
freevm(pde_t *pgdir)
{
uint i, j, da;
if (!pgdir)
panic("freevm: no pgdir\n");
for (i = 0; i < NPDENTRIES; i++) {
da = PTE_ADDR(pgdir[i]);
if (da != 0) {
pte_t *pgtab = (pte_t*) da;
for (j = 0; j < NPTENTRIES; j++) {
if (pgtab[j] != 0) {
uint pa = PTE_ADDR(pgtab[j]);
uint va = PGADDR(i, j, 0);
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if (va >= USERTOP) // done with user part?
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break;
kfree((void *) pa, PGSIZE);
pgtab[j] = 0;
}
}
kfree((void *) da, PGSIZE);
pgdir[i] = 0;
}
}
kfree((void *) pgdir, PGSIZE);
}
int
loaduvm(pde_t *pgdir, char *addr, struct inode *ip, uint offset, uint sz)
{
uint i, pa, n;
pte_t *pte;
if ((uint)addr % PGSIZE != 0)
panic("loaduvm: addr must be page aligned\n");
for (i = 0; i < sz; i += PGSIZE) {
if (!(pte = walkpgdir(pgdir, addr+i, 0)))
panic("loaduvm: address should exist\n");
pa = PTE_ADDR(*pte);
if (sz - i < PGSIZE) n = sz - i;
else n = PGSIZE;
if(readi(ip, (char *)pa, offset+i, n) != n)
return 0;
}
return 1;
}
void
inituvm(pde_t *pgdir, char *addr, char *init, uint sz)
{
uint i, pa, n, off;
pte_t *pte;
for (i = 0; i < sz; i += PGSIZE) {
if (!(pte = walkpgdir(pgdir, (void *)(i+addr), 0)))
panic("inituvm: pte should exist\n");
off = (i+(uint)addr) % PGSIZE;
pa = PTE_ADDR(*pte);
if (sz - i < PGSIZE) n = sz - i;
else n = PGSIZE;
memmove((char *)pa+off, init+i, n);
}
}
pde_t*
copyuvm(pde_t *pgdir, uint sz)
{
pde_t *d = setupkvm();
pte_t *pte;
uint pa, i;
char *mem;
if (!d) return 0;
for (i = 0; i < sz; i += PGSIZE) {
if (!(pte = walkpgdir(pgdir, (void *)i, 0)))
panic("copyuvm: pte should exist\n");
pa = PTE_ADDR(*pte);
if (!(mem = kalloc(PGSIZE)))
return 0;
memmove(mem, (char *)pa, PGSIZE);
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if (!mappages(d, (void *)i, PGSIZE, PADDR(mem), PTE_W|PTE_U))
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return 0;
}
return d;
}
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// Gather about physical memory layout. Called once during boot.
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void
pminit(void)
{
extern char end[];
struct proghdr *ph;
struct elfhdr *elf = (struct elfhdr*)0x10000; // scratch space
if (elf->magic != ELF_MAGIC || elf->phnum != 2)
panic("pminit: need a text and data segment\n");
ph = (struct proghdr*)((uchar*)elf + elf->phoff);
kernend = ((uint)end + PGSIZE) & ~(PGSIZE-1);
kerntext = ph[0].va;
kerndata = ph[1].va;
kerntsz = kerndata - kerntext;
kerndsz = kernend - kerndata;
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freesz = PHYSTOP - kernend;
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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);
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kinit((char *)kernend, freesz);
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}
// Jump to mainc on a properly-allocated kernel stack
void
jkstack(void)
{
char *kstack = kalloc(PGSIZE);
if (!kstack)
panic("jkstack\n");
char *top = kstack + PGSIZE;
jstack((uint) top);
}
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// Allocate one page table for the machine for the kernel address
// space for scheduler processes.
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void
kvmalloc(void)
{
kpgdir = setupkvm();
}
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// Turn on paging.
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void
vminit(void)
{
uint cr0;
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lcr3(PADDR(kpgdir));
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cr0 = rcr0();
cr0 |= CR0_PE|CR0_PG|CR0_AM|CR0_WP|CR0_NE|CR0_TS|CR0_EM|CR0_MP;
cr0 &= ~(CR0_TS|CR0_EM);
lcr0(cr0);
}