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 struct segdesc gdt[NSEGS]; 13 14 // Set up CPU's kernel segment descriptors. 15 // Run once on entry on each CPU. 16 void 17 seginit(void) 18 { 19 struct cpu *c; 20 21 // Map "logical" addresses to virtual addresses using identity map. 22 // Cannot share a CODE descriptor for both kernel and user 23 // because it would have to have DPL_USR, but the CPU forbids 24 // an interrupt from CPL=0 to DPL=3. 25 c = &cpus[cpunum()]; 26 c->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, 0); 27 c->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0); 28 c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, DPL_USER); 29 c->gdt[SEG_UDATA] = SEG(STA_W, 0, 0xffffffff, DPL_USER); 30 31 // Map cpu, and curproc 32 c->gdt[SEG_KCPU] = SEG(STA_W, &c->cpu, 8, 0); 33 34 lgdt(c->gdt, sizeof(c->gdt)); 35 loadgs(SEG_KCPU << 3); 36 37 // Initialize cpu-local storage. 38 cpu = c; 39 proc = 0; 40 } 41 42 // Return the address of the PTE in page table pgdir 43 // that corresponds to virtual address va. If alloc!=0, 44 // create any required page table pages. 45 static pte_t * 46 walkpgdir(pde_t *pgdir, const void *va, int alloc) 47 { 48 pde_t *pde; 49 pte_t *pgtab; 50 51 pde = &pgdir[PDX(va)]; 52 if(*pde & PTE_P){ 53 pgtab = (pte_t*)p2v(PTE_ADDR(*pde)); 54 } else { 55 if(!alloc || (pgtab = (pte_t*)kalloc()) == 0) 56 return 0; 57 // Make sure all those PTE_P bits are zero. 58 memset(pgtab, 0, PGSIZE); 59 // The permissions here are overly generous, but they can 60 // be further restricted by the permissions in the page table 61 // entries, if necessary. 62 *pde = v2p(pgtab) | PTE_P | PTE_W | PTE_U; 63 } 64 return &pgtab[PTX(va)]; 65 } 66 67 // Create PTEs for virtual addresses starting at va that refer to 68 // physical addresses starting at pa. va and size might not 69 // be page-aligned. 70 static int 71 mappages(pde_t *pgdir, void *va, uint size, uint pa, int perm) 72 { 73 char *a, *last; 74 pte_t *pte; 75 76 a = (char*)PGROUNDDOWN((uint)va); 77 last = (char*)PGROUNDDOWN(((uint)va) + size - 1); 78 for(;;){ 79 if((pte = walkpgdir(pgdir, a, 1)) == 0) 80 return -1; 81 if(*pte & PTE_P) 82 panic("remap"); 83 *pte = pa | perm | PTE_P; 84 if(a == last) 85 break; 86 a += PGSIZE; 87 pa += PGSIZE; 88 } 89 return 0; 90 } 91 92 // There is one page table per process, plus one that's used when 93 // a CPU is not running any process (kpgdir). The kernel uses the 94 // current process's page table during system calls and interrupts; 95 // page protection bits prevent user code from using the kernel's 96 // mappings. 97 // 98 // setupkvm() and exec() set up every page table like this: 99 // 100 // 0..KERNBASE: user memory (text+data+stack+heap), mapped to 101 // phys memory allocated by the kernel 102 // KERNBASE..KERNBASE+EXTMEM: mapped to 0..EXTMEM (for I/O space) 103 // KERNBASE+EXTMEM..data: mapped to EXTMEM..V2P(data) 104 // for the kernel's instructions and r/o data 105 // data..KERNBASE+PHYSTOP: mapped to V2P(data)..PHYSTOP, 106 // rw data + free physical memory 107 // 0xfe000000..0: mapped direct (devices such as ioapic) 108 // 109 // The kernel allocates physical memory for its heap and for user memory 110 // between V2P(end) and the end of physical memory (PHYSTOP) 111 // (directly addressable from end..P2V(PHYSTOP)). 112 113 // This table defines the kernel's mappings, which are present in 114 // every process's page table. 115 static struct kmap { 116 void *virt; 117 uint phys_start; 118 uint phys_end; 119 int perm; 120 } kmap[] = { 121 { (void*)KERNBASE, 0, EXTMEM, PTE_W}, // I/O space 122 { (void*)KERNLINK, V2P(KERNLINK), V2P(data), 0}, // kernel text+rodata 123 { (void*)data, V2P(data), PHYSTOP, PTE_W}, // kernel data+memory 124 { (void*)DEVSPACE, DEVSPACE, 0, PTE_W}, // more devices 125 }; 126 127 // Set up kernel part of a page table. 128 pde_t* 129 setupkvm(void) 130 { 131 pde_t *pgdir; 132 struct kmap *k; 133 134 if((pgdir = (pde_t*)kalloc()) == 0) 135 return 0; 136 memset(pgdir, 0, PGSIZE); 137 if (p2v(PHYSTOP) > (void*)DEVSPACE) 138 panic("PHYSTOP too high"); 139 for(k = kmap; k < &kmap[NELEM(kmap)]; k++) 140 if(mappages(pgdir, k->virt, k->phys_end - k->phys_start, 141 (uint)k->phys_start, k->perm) < 0) 142 return 0; 143 return pgdir; 144 } 145 146 // Allocate one page table for the machine for the kernel address 147 // space for scheduler processes. 148 void 149 kvmalloc(void) 150 { 151 kpgdir = setupkvm(); 152 switchkvm(); 153 } 154 155 // Switch h/w page table register to the kernel-only page table, 156 // for when no process is running. 157 void 158 switchkvm(void) 159 { 160 lcr3(v2p(kpgdir)); // switch to the kernel page table 161 } 162 163 // Switch TSS and h/w page table to correspond to process p. 164 void 165 switchuvm(struct proc *p) 166 { 167 pushcli(); 168 cpu->gdt[SEG_TSS] = SEG16(STS_T32A, &cpu->ts, sizeof(cpu->ts)-1, 0); 169 cpu->gdt[SEG_TSS].s = 0; 170 cpu->ts.ss0 = SEG_KDATA << 3; 171 cpu->ts.esp0 = (uint)proc->kstack + KSTACKSIZE; 172 ltr(SEG_TSS << 3); 173 if(p->pgdir == 0) 174 panic("switchuvm: no pgdir"); 175 lcr3(v2p(p->pgdir)); // switch to new address space 176 popcli(); 177 } 178 179 // Load the initcode into address 0 of pgdir. 180 // sz must be less than a page. 181 void 182 inituvm(pde_t *pgdir, char *init, uint sz) 183 { 184 char *mem; 185 186 if(sz >= PGSIZE) 187 panic("inituvm: more than a page"); 188 mem = kalloc(); 189 memset(mem, 0, PGSIZE); 190 mappages(pgdir, 0, PGSIZE, v2p(mem), PTE_W|PTE_U); 191 memmove(mem, init, sz); 192 } 193 194 // Load a program segment into pgdir. addr must be page-aligned 195 // and the pages from addr to addr+sz must already be mapped. 196 int 197 loaduvm(pde_t *pgdir, char *addr, struct inode *ip, uint offset, uint sz) 198 { 199 uint i, pa, n; 200 pte_t *pte; 201 202 if((uint) addr % PGSIZE != 0) 203 panic("loaduvm: addr must be page aligned"); 204 for(i = 0; i < sz; i += PGSIZE){ 205 if((pte = walkpgdir(pgdir, addr+i, 0)) == 0) 206 panic("loaduvm: address should exist"); 207 pa = PTE_ADDR(*pte); 208 if(sz - i < PGSIZE) 209 n = sz - i; 210 else 211 n = PGSIZE; 212 if(readi(ip, p2v(pa), offset+i, n) != n) 213 return -1; 214 } 215 return 0; 216 } 217 218 // Allocate page tables and physical memory to grow process from oldsz to 219 // newsz, which need not be page aligned. Returns new size or 0 on error. 220 int 221 allocuvm(pde_t *pgdir, uint oldsz, uint newsz) 222 { 223 char *mem; 224 uint a; 225 226 if(newsz >= KERNBASE) 227 return 0; 228 if(newsz < oldsz) 229 return oldsz; 230 231 a = PGROUNDUP(oldsz); 232 for(; a < newsz; a += PGSIZE){ 233 mem = kalloc(); 234 if(mem == 0){ 235 cprintf("allocuvm out of memory\n"); 236 deallocuvm(pgdir, newsz, oldsz); 237 return 0; 238 } 239 memset(mem, 0, PGSIZE); 240 mappages(pgdir, (char*)a, PGSIZE, v2p(mem), PTE_W|PTE_U); 241 } 242 return newsz; 243 } 244 245 // Deallocate user pages to bring the process size from oldsz to 246 // newsz. oldsz and newsz need not be page-aligned, nor does newsz 247 // need to be less than oldsz. oldsz can be larger than the actual 248 // process size. Returns the new process size. 249 int 250 deallocuvm(pde_t *pgdir, uint oldsz, uint newsz) 251 { 252 pte_t *pte; 253 uint a, pa; 254 255 if(newsz >= oldsz) 256 return oldsz; 257 258 a = PGROUNDUP(newsz); 259 for(; a < oldsz; a += PGSIZE){ 260 pte = walkpgdir(pgdir, (char*)a, 0); 261 if(!pte) 262 a += (NPTENTRIES - 1) * PGSIZE; 263 else if((*pte & PTE_P) != 0){ 264 pa = PTE_ADDR(*pte); 265 if(pa == 0) 266 panic("kfree"); 267 char *v = p2v(pa); 268 kfree(v); 269 *pte = 0; 270 } 271 } 272 return newsz; 273 } 274 275 // Free a page table and all the physical memory pages 276 // in the user part. 277 void 278 freevm(pde_t *pgdir) 279 { 280 uint i; 281 282 if(pgdir == 0) 283 panic("freevm: no pgdir"); 284 deallocuvm(pgdir, KERNBASE, 0); 285 for(i = 0; i < NPDENTRIES; i++){ 286 if(pgdir[i] & PTE_P){ 287 char * v = p2v(PTE_ADDR(pgdir[i])); 288 kfree(v); 289 } 290 } 291 kfree((char*)pgdir); 292 } 293 294 // Clear PTE_U on a page. Used to create an inaccessible 295 // page beneath the user stack. 296 void 297 clearpteu(pde_t *pgdir, char *uva) 298 { 299 pte_t *pte; 300 301 pte = walkpgdir(pgdir, uva, 0); 302 if(pte == 0) 303 panic("clearpteu"); 304 *pte &= ~PTE_U; 305 } 306 307 // Given a parent process's page table, create a copy 308 // of it for a child. 309 pde_t* 310 copyuvm(pde_t *pgdir, uint sz) 311 { 312 pde_t *d; 313 pte_t *pte; 314 uint pa, i; 315 char *mem; 316 317 if((d = setupkvm()) == 0) 318 return 0; 319 for(i = 0; i < sz; i += PGSIZE){ 320 if((pte = walkpgdir(pgdir, (void *) i, 0)) == 0) 321 panic("copyuvm: pte should exist"); 322 if(!(*pte & PTE_P)) 323 panic("copyuvm: page not present"); 324 pa = PTE_ADDR(*pte); 325 if((mem = kalloc()) == 0) 326 goto bad; 327 memmove(mem, (char*)p2v(pa), PGSIZE); 328 if(mappages(d, (void*)i, PGSIZE, v2p(mem), PTE_W|PTE_U) < 0) 329 goto bad; 330 } 331 return d; 332 333 bad: 334 freevm(d); 335 return 0; 336 } 337 338 //PAGEBREAK! 339 // Map user virtual address to kernel address. 340 char* 341 uva2ka(pde_t *pgdir, char *uva) 342 { 343 pte_t *pte; 344 345 pte = walkpgdir(pgdir, uva, 0); 346 if((*pte & PTE_P) == 0) 347 return 0; 348 if((*pte & PTE_U) == 0) 349 return 0; 350 return (char*)p2v(PTE_ADDR(*pte)); 351 } 352 353 // Copy len bytes from p to user address va in page table pgdir. 354 // Most useful when pgdir is not the current page table. 355 // uva2ka ensures this only works for PTE_U pages. 356 int 357 copyout(pde_t *pgdir, uint va, void *p, uint len) 358 { 359 char *buf, *pa0; 360 uint n, va0; 361 362 buf = (char*)p; 363 while(len > 0){ 364 va0 = (uint)PGROUNDDOWN(va); 365 pa0 = uva2ka(pgdir, (char*)va0); 366 if(pa0 == 0) 367 return -1; 368 n = PGSIZE - (va - va0); 369 if(n > len) 370 n = len; 371 memmove(pa0 + (va - va0), buf, n); 372 len -= n; 373 buf += n; 374 va = va0 + PGSIZE; 375 } 376 return 0; 377 } 378