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 proc -- 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 if(p == 0) 167 panic("switchuvm: no process"); 168 if(p->kstack == 0) 169 panic("switchuvm: no kstack"); 170 if(p->pgdir == 0) 171 panic("switchuvm: no pgdir"); 172 173 pushcli(); 174 cpu->gdt[SEG_TSS] = SEG16(STS_T32A, &cpu->ts, sizeof(cpu->ts)-1, 0); 175 cpu->gdt[SEG_TSS].s = 0; 176 cpu->ts.ss0 = SEG_KDATA << 3; 177 cpu->ts.esp0 = (uint)p->kstack + KSTACKSIZE; 178 // setting IOPL=0 in eflags *and* iomb beyond the tss segment limit 179 // forbids I/O instructions (e.g., inb and outb) from user space 180 cpu->ts.iomb = (ushort) 0xFFFF; 181 ltr(SEG_TSS << 3); 182 lcr3(V2P(p->pgdir)); // switch to process's address space 183 popcli(); 184 } 185 186 // Load the initcode into address 0 of pgdir. 187 // sz must be less than a page. 188 void 189 inituvm(pde_t *pgdir, char *init, uint sz) 190 { 191 char *mem; 192 193 if(sz >= PGSIZE) 194 panic("inituvm: more than a page"); 195 mem = kalloc(); 196 memset(mem, 0, PGSIZE); 197 mappages(pgdir, 0, PGSIZE, V2P(mem), PTE_W|PTE_U); 198 memmove(mem, init, sz); 199 } 200 201 // Load a program segment into pgdir. addr must be page-aligned 202 // and the pages from addr to addr+sz must already be mapped. 203 int 204 loaduvm(pde_t *pgdir, char *addr, struct inode *ip, uint offset, uint sz) 205 { 206 uint i, pa, n; 207 pte_t *pte; 208 209 if((uint) addr % PGSIZE != 0) 210 panic("loaduvm: addr must be page aligned"); 211 for(i = 0; i < sz; i += PGSIZE){ 212 if((pte = walkpgdir(pgdir, addr+i, 0)) == 0) 213 panic("loaduvm: address should exist"); 214 pa = PTE_ADDR(*pte); 215 if(sz - i < PGSIZE) 216 n = sz - i; 217 else 218 n = PGSIZE; 219 if(readi(ip, P2V(pa), offset+i, n) != n) 220 return -1; 221 } 222 return 0; 223 } 224 225 // Allocate page tables and physical memory to grow process from oldsz to 226 // newsz, which need not be page aligned. Returns new size or 0 on error. 227 int 228 allocuvm(pde_t *pgdir, uint oldsz, uint newsz) 229 { 230 char *mem; 231 uint a; 232 233 if(newsz >= KERNBASE) 234 return 0; 235 if(newsz < oldsz) 236 return oldsz; 237 238 a = PGROUNDUP(oldsz); 239 for(; a < newsz; a += PGSIZE){ 240 mem = kalloc(); 241 if(mem == 0){ 242 cprintf("allocuvm out of memory\n"); 243 deallocuvm(pgdir, newsz, oldsz); 244 return 0; 245 } 246 memset(mem, 0, PGSIZE); 247 if(mappages(pgdir, (char*)a, PGSIZE, V2P(mem), PTE_W|PTE_U) < 0){ 248 cprintf("allocuvm out of memory (2)\n"); 249 deallocuvm(pgdir, newsz, oldsz); 250 kfree(mem); 251 return 0; 252 } 253 } 254 return newsz; 255 } 256 257 // Deallocate user pages to bring the process size from oldsz to 258 // newsz. oldsz and newsz need not be page-aligned, nor does newsz 259 // need to be less than oldsz. oldsz can be larger than the actual 260 // process size. Returns the new process size. 261 int 262 deallocuvm(pde_t *pgdir, uint oldsz, uint newsz) 263 { 264 pte_t *pte; 265 uint a, pa; 266 267 if(newsz >= oldsz) 268 return oldsz; 269 270 a = PGROUNDUP(newsz); 271 for(; a < oldsz; a += PGSIZE){ 272 pte = walkpgdir(pgdir, (char*)a, 0); 273 if(!pte) 274 a = PGADDR(PDX(a) + 1, 0, 0) - PGSIZE; 275 else if((*pte & PTE_P) != 0){ 276 pa = PTE_ADDR(*pte); 277 if(pa == 0) 278 panic("kfree"); 279 char *v = P2V(pa); 280 kfree(v); 281 *pte = 0; 282 } 283 } 284 return newsz; 285 } 286 287 // Free a page table and all the physical memory pages 288 // in the user part. 289 void 290 freevm(pde_t *pgdir) 291 { 292 uint i; 293 294 if(pgdir == 0) 295 panic("freevm: no pgdir"); 296 deallocuvm(pgdir, KERNBASE, 0); 297 for(i = 0; i < NPDENTRIES; i++){ 298 if(pgdir[i] & PTE_P){ 299 char * v = P2V(PTE_ADDR(pgdir[i])); 300 kfree(v); 301 } 302 } 303 kfree((char*)pgdir); 304 } 305 306 // Clear PTE_U on a page. Used to create an inaccessible 307 // page beneath the user stack. 308 void 309 clearpteu(pde_t *pgdir, char *uva) 310 { 311 pte_t *pte; 312 313 pte = walkpgdir(pgdir, uva, 0); 314 if(pte == 0) 315 panic("clearpteu"); 316 *pte &= ~PTE_U; 317 } 318 319 // Given a parent process's page table, create a copy 320 // of it for a child. 321 pde_t* 322 copyuvm(pde_t *pgdir, uint sz) 323 { 324 pde_t *d; 325 pte_t *pte; 326 uint pa, i, flags; 327 char *mem; 328 329 if((d = setupkvm()) == 0) 330 return 0; 331 for(i = 0; i < sz; i += PGSIZE){ 332 if((pte = walkpgdir(pgdir, (void *) i, 0)) == 0) 333 panic("copyuvm: pte should exist"); 334 if(!(*pte & PTE_P)) 335 panic("copyuvm: page not present"); 336 pa = PTE_ADDR(*pte); 337 flags = PTE_FLAGS(*pte); 338 if((mem = kalloc()) == 0) 339 goto bad; 340 memmove(mem, (char*)P2V(pa), PGSIZE); 341 if(mappages(d, (void*)i, PGSIZE, V2P(mem), flags) < 0) 342 goto bad; 343 } 344 return d; 345 346 bad: 347 freevm(d); 348 return 0; 349 } 350 351 //PAGEBREAK! 352 // Map user virtual address to kernel address. 353 char* 354 uva2ka(pde_t *pgdir, char *uva) 355 { 356 pte_t *pte; 357 358 pte = walkpgdir(pgdir, uva, 0); 359 if((*pte & PTE_P) == 0) 360 return 0; 361 if((*pte & PTE_U) == 0) 362 return 0; 363 return (char*)P2V(PTE_ADDR(*pte)); 364 } 365 366 // Copy len bytes from p to user address va in page table pgdir. 367 // Most useful when pgdir is not the current page table. 368 // uva2ka ensures this only works for PTE_U pages. 369 int 370 copyout(pde_t *pgdir, uint va, void *p, uint len) 371 { 372 char *buf, *pa0; 373 uint n, va0; 374 375 buf = (char*)p; 376 while(len > 0){ 377 va0 = (uint)PGROUNDDOWN(va); 378 pa0 = uva2ka(pgdir, (char*)va0); 379 if(pa0 == 0) 380 return -1; 381 n = PGSIZE - (va - va0); 382 if(n > len) 383 n = len; 384 memmove(pa0 + (va - va0), buf, n); 385 len -= n; 386 buf += n; 387 va = va0 + PGSIZE; 388 } 389 return 0; 390 } 391 392 //PAGEBREAK! 393 // Blank page. 394 //PAGEBREAK! 395 // Blank page. 396 //PAGEBREAK! 397 // Blank page. 398 399