diff options
Diffstat (limited to 'vm.c')
| -rw-r--r-- | vm.c | 394 |
1 files changed, 0 insertions, 394 deletions
@@ -1,394 +0,0 @@ -#include "param.h" -#include "types.h" -#include "defs.h" -#include "x86.h" -#include "memlayout.h" -#include "mmu.h" -#include "proc.h" -#include "elf.h" - -extern char data[]; // defined by kernel.ld -pde_t *kpgdir; // for use in scheduler() - -// Set up CPU's kernel segment descriptors. -// Run once on entry on each CPU. -void -seginit(void) -{ - struct cpu *c; - - // 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. - c = &cpus[cpuid()]; - 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, 0, 0xffffffff, DPL_USER); - c->gdt[SEG_UDATA] = SEG(STA_W, 0, 0xffffffff, DPL_USER); - lgdt(c->gdt, sizeof(c->gdt)); -} - -// Return the address of the PTE in page table pgdir -// 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, int alloc) -{ - pde_t *pde; - pte_t *pgtab; - - pde = &pgdir[PDX(va)]; - if(*pde & PTE_P){ - pgtab = (pte_t*)P2V(PTE_ADDR(*pde)); - } else { - if(!alloc || (pgtab = (pte_t*)kalloc()) == 0) - return 0; - // 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 = V2P(pgtab) | PTE_P | PTE_W | PTE_U; - } - return &pgtab[PTX(va)]; -} - -// Create PTEs for virtual addresses starting at va that refer to -// physical addresses starting at pa. va and size might not -// be page-aligned. -static int -mappages(pde_t *pgdir, void *va, uint size, uint pa, int perm) -{ - char *a, *last; - pte_t *pte; - - a = (char*)PGROUNDDOWN((uint)va); - last = (char*)PGROUNDDOWN(((uint)va) + size - 1); - for(;;){ - if((pte = walkpgdir(pgdir, a, 1)) == 0) - return -1; - if(*pte & PTE_P) - panic("remap"); - *pte = pa | perm | PTE_P; - if(a == last) - break; - a += PGSIZE; - pa += PGSIZE; - } - return 0; -} - -// There is one page table per process, plus one that's used when -// a CPU is not running any process (kpgdir). The kernel uses the -// current process's page table during system calls and interrupts; -// page protection bits prevent user code from using the kernel's -// mappings. -// -// setupkvm() and exec() set up every page table like this: -// -// 0..KERNBASE: user memory (text+data+stack+heap), mapped to -// phys memory allocated by the kernel -// KERNBASE..KERNBASE+EXTMEM: mapped to 0..EXTMEM (for I/O space) -// KERNBASE+EXTMEM..data: mapped to EXTMEM..V2P(data) -// for the kernel's instructions and r/o data -// data..KERNBASE+PHYSTOP: mapped to V2P(data)..PHYSTOP, -// rw data + free physical memory -// 0xfe000000..0: mapped direct (devices such as ioapic) -// -// The kernel allocates physical memory for its heap and for user memory -// between V2P(end) and the end of physical memory (PHYSTOP) -// (directly addressable from end..P2V(PHYSTOP)). - -// This table defines the kernel's mappings, which are present in -// every process's page table. -static struct kmap { - void *virt; - uint phys_start; - uint phys_end; - int perm; -} kmap[] = { - { (void*)KERNBASE, 0, EXTMEM, PTE_W}, // I/O space - { (void*)KERNLINK, V2P(KERNLINK), V2P(data), 0}, // kern text+rodata - { (void*)data, V2P(data), PHYSTOP, PTE_W}, // kern data+memory - { (void*)DEVSPACE, DEVSPACE, 0, PTE_W}, // more devices -}; - -// Set up kernel part of a page table. -pde_t* -setupkvm(void) -{ - pde_t *pgdir; - struct kmap *k; - - if((pgdir = (pde_t*)kalloc()) == 0) - return 0; - memset(pgdir, 0, PGSIZE); - if (P2V(PHYSTOP) > (void*)DEVSPACE) - panic("PHYSTOP too high"); - for(k = kmap; k < &kmap[NELEM(kmap)]; k++) - if(mappages(pgdir, k->virt, k->phys_end - k->phys_start, - (uint)k->phys_start, k->perm) < 0) { - freevm(pgdir); - return 0; - } - return pgdir; -} - -// Allocate one page table for the machine for the kernel address -// space for scheduler processes. -void -kvmalloc(void) -{ - kpgdir = setupkvm(); - switchkvm(); -} - -// Switch h/w page table register to the kernel-only page table, -// for when no process is running. -void -switchkvm(void) -{ - lcr3(V2P(kpgdir)); // switch to the kernel page table -} - -// Switch TSS and h/w page table to correspond to process p. -void -switchuvm(struct proc *p) -{ - if(p == 0) - panic("switchuvm: no process"); - if(p->kstack == 0) - panic("switchuvm: no kstack"); - if(p->pgdir == 0) - panic("switchuvm: no pgdir"); - - pushcli(); - mycpu()->gdt[SEG_TSS] = SEG16(STS_T32A, &mycpu()->ts, - sizeof(mycpu()->ts)-1, 0); - mycpu()->gdt[SEG_TSS].s = 0; - mycpu()->ts.ss0 = SEG_KDATA << 3; - mycpu()->ts.esp0 = (uint)p->kstack + KSTACKSIZE; - // setting IOPL=0 in eflags *and* iomb beyond the tss segment limit - // forbids I/O instructions (e.g., inb and outb) from user space - mycpu()->ts.iomb = (ushort) 0xFFFF; - ltr(SEG_TSS << 3); - lcr3(V2P(p->pgdir)); // switch to process's address space - popcli(); -} - -// Load the initcode into address 0 of pgdir. -// sz must be less than a page. -void -inituvm(pde_t *pgdir, char *init, uint sz) -{ - char *mem; - - if(sz >= PGSIZE) - panic("inituvm: more than a page"); - mem = kalloc(); - memset(mem, 0, PGSIZE); - mappages(pgdir, 0, PGSIZE, V2P(mem), PTE_W|PTE_U); - memmove(mem, init, sz); -} - -// Load a program segment into pgdir. addr must be page-aligned -// and the pages from addr to addr+sz must already be mapped. -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"); - for(i = 0; i < sz; i += PGSIZE){ - if((pte = walkpgdir(pgdir, addr+i, 0)) == 0) - panic("loaduvm: address should exist"); - pa = PTE_ADDR(*pte); - if(sz - i < PGSIZE) - n = sz - i; - else - n = PGSIZE; - if(readi(ip, P2V(pa), offset+i, n) != n) - return -1; - } - return 0; -} - -// Allocate page tables and physical memory to grow process from oldsz to -// newsz, which need not be page aligned. Returns new size or 0 on error. -int -allocuvm(pde_t *pgdir, uint oldsz, uint newsz) -{ - char *mem; - uint a; - - if(newsz >= KERNBASE) - return 0; - if(newsz < oldsz) - return oldsz; - - a = PGROUNDUP(oldsz); - for(; a < newsz; a += PGSIZE){ - mem = kalloc(); - if(mem == 0){ - cprintf("allocuvm out of memory\n"); - deallocuvm(pgdir, newsz, oldsz); - return 0; - } - memset(mem, 0, PGSIZE); - if(mappages(pgdir, (char*)a, PGSIZE, V2P(mem), PTE_W|PTE_U) < 0){ - cprintf("allocuvm out of memory (2)\n"); - deallocuvm(pgdir, newsz, oldsz); - kfree(mem); - return 0; - } - } - return newsz; -} - -// Deallocate user pages to bring the process size from oldsz to -// newsz. oldsz and newsz need not be page-aligned, nor does newsz -// need to be less than oldsz. oldsz can be larger than the actual -// process size. Returns the new process size. -int -deallocuvm(pde_t *pgdir, uint oldsz, uint newsz) -{ - pte_t *pte; - uint a, pa; - - if(newsz >= oldsz) - return oldsz; - - a = PGROUNDUP(newsz); - for(; a < oldsz; a += PGSIZE){ - pte = walkpgdir(pgdir, (char*)a, 0); - if(!pte) - a = PGADDR(PDX(a) + 1, 0, 0) - PGSIZE; - else if((*pte & PTE_P) != 0){ - pa = PTE_ADDR(*pte); - if(pa == 0) - panic("kfree"); - char *v = P2V(pa); - kfree(v); - *pte = 0; - } - } - return newsz; -} - -// Free a page table and all the physical memory pages -// in the user part. -void -freevm(pde_t *pgdir) -{ - uint i; - - if(pgdir == 0) - panic("freevm: no pgdir"); - deallocuvm(pgdir, KERNBASE, 0); - for(i = 0; i < NPDENTRIES; i++){ - if(pgdir[i] & PTE_P){ - char * v = P2V(PTE_ADDR(pgdir[i])); - kfree(v); - } - } - kfree((char*)pgdir); -} - -// Clear PTE_U on a page. Used to create an inaccessible -// page beneath the user stack. -void -clearpteu(pde_t *pgdir, char *uva) -{ - pte_t *pte; - - pte = walkpgdir(pgdir, uva, 0); - if(pte == 0) - panic("clearpteu"); - *pte &= ~PTE_U; -} - -// Given a parent process's page table, create a copy -// of it for a child. -pde_t* -copyuvm(pde_t *pgdir, uint sz) -{ - pde_t *d; - pte_t *pte; - uint pa, i, flags; - char *mem; - - if((d = setupkvm()) == 0) - return 0; - for(i = 0; i < sz; i += PGSIZE){ - if((pte = walkpgdir(pgdir, (void *) i, 0)) == 0) - panic("copyuvm: pte should exist"); - if(!(*pte & PTE_P)) - panic("copyuvm: page not present"); - pa = PTE_ADDR(*pte); - flags = PTE_FLAGS(*pte); - if((mem = kalloc()) == 0) - goto bad; - memmove(mem, (char*)P2V(pa), PGSIZE); - if(mappages(d, (void*)i, PGSIZE, V2P(mem), flags) < 0) { - kfree(mem); - goto bad; - } - } - return d; - -bad: - freevm(d); - return 0; -} - -//PAGEBREAK! -// Map user virtual address to kernel address. -char* -uva2ka(pde_t *pgdir, char *uva) -{ - pte_t *pte; - - pte = walkpgdir(pgdir, uva, 0); - if((*pte & PTE_P) == 0) - return 0; - if((*pte & PTE_U) == 0) - return 0; - return (char*)P2V(PTE_ADDR(*pte)); -} - -// Copy len bytes from p to user address va in page table pgdir. -// Most useful when pgdir is not the current page table. -// uva2ka ensures this only works for PTE_U pages. -int -copyout(pde_t *pgdir, uint va, void *p, uint len) -{ - char *buf, *pa0; - uint n, va0; - - buf = (char*)p; - while(len > 0){ - va0 = (uint)PGROUNDDOWN(va); - pa0 = uva2ka(pgdir, (char*)va0); - if(pa0 == 0) - return -1; - n = PGSIZE - (va - va0); - if(n > len) - n = len; - memmove(pa0 + (va - va0), buf, n); - len -= n; - buf += n; - va = va0 + PGSIZE; - } - return 0; -} - -//PAGEBREAK! -// Blank page. -//PAGEBREAK! -// Blank page. -//PAGEBREAK! -// Blank page. - |