1 #include "param.h" 2 #include "types.h" 3 #include "defs.h" 4 #include "x86.h" 5 #include "memlayout.h" 6 #include "mmu.h" 7 #include "proc.h" 8 #include "elf.h" 9 10 extern char data[]; // defined by kernel.ld 11 pde_t *kpgdir; // for use in scheduler() 12 13 // Set up CPU's kernel segment descriptors. 14 // Run once on entry on each CPU. 15 void 16 seginit(void) 17 { 18 struct cpu *c; 19 20 // Map "logical" addresses to virtual addresses using identity map. 21 // Cannot share a CODE descriptor for both kernel and user 22 // because it would have to have DPL_USR, but the CPU forbids 23 // an interrupt from CPL=0 to DPL=3. 24 c = &cpus[cpunum()]; 25 c->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, 0); 26 c->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0); 27 c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, DPL_USER); 28 c->gdt[SEG_UDATA] = SEG(STA_W, 0, 0xffffffff, DPL_USER); 29 30 // Map cpu and curproc -- these are private per cpu. 31 c->gdt[SEG_KCPU] = SEG(STA_W, &c->cpu, 8, 0); 32 33 lgdt(c->gdt, sizeof(c->gdt)); 34 loadgs(SEG_KCPU << 3); 35 36 // Initialize cpu-local storage. 37 cpu = c; 38 proc = 0; 39 } 40 41 // Return the address of the PTE in page table pgdir 42 // that corresponds to virtual address va. If alloc!=0, 43 // create any required page table pages. 44 static pte_t * 45 walkpgdir(pde_t *pgdir, const void *va, int alloc) 46 { 47 pde_t *pde; 48 pte_t *pgtab; 49 50 pde = &pgdir[PDX(va)]; 51 if(*pde & PTE_P){ 52 pgtab = (pte_t*)P2V(PTE_ADDR(*pde)); 53 } else { 54 if(!alloc || (pgtab = (pte_t*)kalloc()) == 0) 55 return 0; 56 // Make sure all those PTE_P bits are zero. 57 memset(pgtab, 0, PGSIZE); 58 // The permissions here are overly generous, but they can 59 // be further restricted by the permissions in the page table 60 // entries, if necessary. 61 *pde = V2P(pgtab) | PTE_P | PTE_W | PTE_U; 62 } 63 return &pgtab[PTX(va)]; 64 } 65 66 // Create PTEs for virtual addresses starting at va that refer to 67 // physical addresses starting at pa. va and size might not 68 // be page-aligned. 69 static int 70 mappages(pde_t *pgdir, void *va, uint size, uint pa, int perm) 71 { 72 char *a, *last; 73 pte_t *pte; 74 75 a = (char*)PGROUNDDOWN((uint)va); 76 last = (char*)PGROUNDDOWN(((uint)va) + size - 1); 77 for(;;){ 78 if((pte = walkpgdir(pgdir, a, 1)) == 0) 79 return -1; 80 if(*pte & PTE_P) 81 panic("remap"); 82 *pte = pa | perm | PTE_P; 83 if(a == last) 84 break; 85 a += PGSIZE; 86 pa += PGSIZE; 87 } 88 return 0; 89 } 90 91 // There is one page table per process, plus one that's used when 92 // a CPU is not running any process (kpgdir). The kernel uses the 93 // current process's page table during system calls and interrupts; 94 // page protection bits prevent user code from using the kernel's 95 // mappings. 96 // 97 // setupkvm() and exec() set up every page table like this: 98 // 99 // 0..KERNBASE: user memory (text+data+stack+heap), mapped to 100 // phys memory allocated by the kernel 101 // KERNBASE..KERNBASE+EXTMEM: mapped to 0..EXTMEM (for I/O space) 102 // KERNBASE+EXTMEM..data: mapped to EXTMEM..V2P(data) 103 // for the kernel's instructions and r/o data 104 // data..KERNBASE+PHYSTOP: mapped to V2P(data)..PHYSTOP, 105 // rw data + free physical memory 106 // 0xfe000000..0: mapped direct (devices such as ioapic) 107 // 108 // The kernel allocates physical memory for its heap and for user memory 109 // between V2P(end) and the end of physical memory (PHYSTOP) 110 // (directly addressable from end..P2V(PHYSTOP)). 111 112 // This table defines the kernel's mappings, which are present in 113 // every process's page table. 114 static struct kmap { 115 void *virt; 116 uint phys_start; 117 uint phys_end; 118 int perm; 119 } kmap[] = { 120 { (void*)KERNBASE, 0, EXTMEM, PTE_W}, // I/O space 121 { (void*)KERNLINK, V2P(KERNLINK), V2P(data), 0}, // kern text+rodata 122 { (void*)data, V2P(data), PHYSTOP, PTE_W}, // kern data+memory 123 { (void*)DEVSPACE, DEVSPACE, 0, PTE_W}, // more devices 124 }; 125 126 // Set up kernel part of a page table. 127 pde_t* 128 setupkvm(void) 129 { 130 pde_t *pgdir; 131 struct kmap *k; 132 133 if((pgdir = (pde_t*)kalloc()) == 0) 134 return 0; 135 memset(pgdir, 0, PGSIZE); 136 if (P2V(PHYSTOP) > (void*)DEVSPACE) 137 panic("PHYSTOP too high"); 138 for(k = kmap; k < &kmap[NELEM(kmap)]; k++) 139 if(mappages(pgdir, k->virt, k->phys_end - k->phys_start, 140 (uint)k->phys_start, k->perm) < 0) 141 return 0; 142 return pgdir; 143 } 144 145 // Allocate one page table for the machine for the kernel address 146 // space for scheduler processes. 147 void 148 kvmalloc(void) 149 { 150 kpgdir = setupkvm(); 151 switchkvm(); 152 } 153 154 // Switch h/w page table register to the kernel-only page table, 155 // for when no process is running. 156 void 157 switchkvm(void) 158 { 159 lcr3(V2P(kpgdir)); // switch to the kernel page table 160 } 161 162 // Switch TSS and h/w page table to correspond to process p. 163 void 164 switchuvm(struct proc *p) 165 { 166 pushcli(); 167 cpu->gdt[SEG_TSS] = SEG16(STS_T32A, &cpu->ts, sizeof(cpu->ts)-1, 0); 168 cpu->gdt[SEG_TSS].s = 0; 169 cpu->ts.ss0 = SEG_KDATA << 3; 170 cpu->ts.esp0 = (uint)proc->kstack + KSTACKSIZE; 171 // setting IOPL=0 in eflags *and* iomb beyond the tss segment limit 172 // forbids I/O instructions (e.g., inb and outb) from user space 173 cpu->ts.iomb = (ushort) 0xFFFF; 174 ltr(SEG_TSS << 3); 175 if(p->pgdir == 0) 176 panic("switchuvm: no pgdir"); 177 lcr3(V2P(p->pgdir)); // switch to process's address space 178 popcli(); 179 } 180 181 // Load the initcode into address 0 of pgdir. 182 // sz must be less than a page. 183 void 184 inituvm(pde_t *pgdir, char *init, uint sz) 185 { 186 char *mem; 187 188 if(sz >= PGSIZE) 189 panic("inituvm: more than a page"); 190 mem = kalloc(); 191 memset(mem, 0, PGSIZE); 192 mappages(pgdir, 0, PGSIZE, V2P(mem), PTE_W|PTE_U); 193 memmove(mem, init, sz); 194 } 195 196 // Load a program segment into pgdir. addr must be page-aligned 197 // and the pages from addr to addr+sz must already be mapped. 198 int 199 loaduvm(pde_t *pgdir, char *addr, struct inode *ip, uint offset, uint sz) 200 { 201 uint i, pa, n; 202 pte_t *pte; 203 204 if((uint) addr % PGSIZE != 0) 205 panic("loaduvm: addr must be page aligned"); 206 for(i = 0; i < sz; i += PGSIZE){ 207 if((pte = walkpgdir(pgdir, addr+i, 0)) == 0) 208 panic("loaduvm: address should exist"); 209 pa = PTE_ADDR(*pte); 210 if(sz - i < PGSIZE) 211 n = sz - i; 212 else 213 n = PGSIZE; 214 if(readi(ip, P2V(pa), offset+i, n) != n) 215 return -1; 216 } 217 return 0; 218 } 219 220 // Allocate page tables and physical memory to grow process from oldsz to 221 // newsz, which need not be page aligned. Returns new size or 0 on error. 222 int 223 allocuvm(pde_t *pgdir, uint oldsz, uint newsz) 224 { 225 char *mem; 226 uint a; 227 228 if(newsz >= KERNBASE) 229 return 0; 230 if(newsz < oldsz) 231 return oldsz; 232 233 a = PGROUNDUP(oldsz); 234 for(; a < newsz; a += PGSIZE){ 235 mem = kalloc(); 236 if(mem == 0){ 237 cprintf("allocuvm out of memory\n"); 238 deallocuvm(pgdir, newsz, oldsz); 239 return 0; 240 } 241 memset(mem, 0, PGSIZE); 242 if(mappages(pgdir, (char*)a, PGSIZE, V2P(mem), PTE_W|PTE_U) < 0){ 243 cprintf("allocuvm out of memory (2)\n"); 244 deallocuvm(pgdir, newsz, oldsz); 245 kfree(mem); 246 return 0; 247 } 248 } 249 return newsz; 250 } 251 252 // Deallocate user pages to bring the process size from oldsz to 253 // newsz. oldsz and newsz need not be page-aligned, nor does newsz 254 // need to be less than oldsz. oldsz can be larger than the actual 255 // process size. Returns the new process size. 256 int 257 deallocuvm(pde_t *pgdir, uint oldsz, uint newsz) 258 { 259 pte_t *pte; 260 uint a, pa; 261 262 if(newsz >= oldsz) 263 return oldsz; 264 265 a = PGROUNDUP(newsz); 266 for(; a < oldsz; a += PGSIZE){ 267 pte = walkpgdir(pgdir, (char*)a, 0); 268 if(!pte) 269 a += (NPTENTRIES - 1) * PGSIZE; 270 else if((*pte & PTE_P) != 0){ 271 pa = PTE_ADDR(*pte); 272 if(pa == 0) 273 panic("kfree"); 274 char *v = P2V(pa); 275 kfree(v); 276 *pte = 0; 277 } 278 } 279 return newsz; 280 } 281 282 // Free a page table and all the physical memory pages 283 // in the user part. 284 void 285 freevm(pde_t *pgdir) 286 { 287 uint i; 288 289 if(pgdir == 0) 290 panic("freevm: no pgdir"); 291 deallocuvm(pgdir, KERNBASE, 0); 292 for(i = 0; i < NPDENTRIES; i++){ 293 if(pgdir[i] & PTE_P){ 294 char * v = P2V(PTE_ADDR(pgdir[i])); 295 kfree(v); 296 } 297 } 298 kfree((char*)pgdir); 299 } 300 301 // Clear PTE_U on a page. Used to create an inaccessible 302 // page beneath the user stack. 303 void 304 clearpteu(pde_t *pgdir, char *uva) 305 { 306 pte_t *pte; 307 308 pte = walkpgdir(pgdir, uva, 0); 309 if(pte == 0) 310 panic("clearpteu"); 311 *pte &= ~PTE_U; 312 } 313 314 // Given a parent process's page table, create a copy 315 // of it for a child. 316 pde_t* 317 copyuvm(pde_t *pgdir, uint sz) 318 { 319 pde_t *d; 320 pte_t *pte; 321 uint pa, i, flags; 322 char *mem; 323 324 if((d = setupkvm()) == 0) 325 return 0; 326 for(i = 0; i < sz; i += PGSIZE){ 327 if((pte = walkpgdir(pgdir, (void *) i, 0)) == 0) 328 panic("copyuvm: pte should exist"); 329 if(!(*pte & PTE_P)) 330 panic("copyuvm: page not present"); 331 pa = PTE_ADDR(*pte); 332 flags = PTE_FLAGS(*pte); 333 if((mem = kalloc()) == 0) 334 goto bad; 335 memmove(mem, (char*)P2V(pa), PGSIZE); 336 if(mappages(d, (void*)i, PGSIZE, V2P(mem), flags) < 0) 337 goto bad; 338 } 339 return d; 340 341 bad: 342 freevm(d); 343 return 0; 344 } 345 346 //PAGEBREAK! 347 // Map user virtual address to kernel address. 348 char* 349 uva2ka(pde_t *pgdir, char *uva) 350 { 351 pte_t *pte; 352 353 pte = walkpgdir(pgdir, uva, 0); 354 if((*pte & PTE_P) == 0) 355 return 0; 356 if((*pte & PTE_U) == 0) 357 return 0; 358 return (char*)P2V(PTE_ADDR(*pte)); 359 } 360 361 // Copy len bytes from p to user address va in page table pgdir. 362 // Most useful when pgdir is not the current page table. 363 // uva2ka ensures this only works for PTE_U pages. 364 int 365 copyout(pde_t *pgdir, uint va, void *p, uint len) 366 { 367 char *buf, *pa0; 368 uint n, va0; 369 370 buf = (char*)p; 371 while(len > 0){ 372 va0 = (uint)PGROUNDDOWN(va); 373 pa0 = uva2ka(pgdir, (char*)va0); 374 if(pa0 == 0) 375 return -1; 376 n = PGSIZE - (va - va0); 377 if(n > len) 378 n = len; 379 memmove(pa0 + (va - va0), buf, n); 380 len -= n; 381 buf += n; 382 va = va0 + PGSIZE; 383 } 384 return 0; 385 } 386 387 //PAGEBREAK! 388 // Blank page. 389 //PAGEBREAK! 390 // Blank page. 391 //PAGEBREAK! 392 // Blank page. 393 394