drivers/lguest/page_tables.c

   1 /* Shadow page table operations.
   2  * Copyright (C) Rusty Russell IBM Corporation 2006.
   3  * GPL v2 and any later version */
   4 #include <linux/mm.h>
   5 #include <linux/types.h>
   6 #include <linux/spinlock.h>
   7 #include <linux/random.h>
   8 #include <linux/percpu.h>
   9 #include <asm/tlbflush.h>
  10 #include "lg.h"
  11
  12 #define PTES_PER_PAGE_SHIFT 10
  13 #define PTES_PER_PAGE (1 << PTES_PER_PAGE_SHIFT)
  14 #define SWITCHER_PGD_INDEX (PTES_PER_PAGE - 1)
  15
  16 static DEFINE_PER_CPU(spte_t *, switcher_pte_pages);
  17 #define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)
  18
  19 static unsigned vaddr_to_pgd_index(unsigned long vaddr)
  20 {
  21         return vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT);
  22 }
  23
  24 /* These access the shadow versions (ie. the ones used by the CPU). */
  25 static spgd_t *spgd_addr(struct lguest *lg, u32 i, unsigned long vaddr)
  26 {
  27         unsigned int index = vaddr_to_pgd_index(vaddr);
  28
  29         if (index >= SWITCHER_PGD_INDEX) {
  30                 kill_guest(lg, "attempt to access switcher pages");
  31                 index = 0;
  32         }
  33         return &lg->pgdirs[i].pgdir[index];
  34 }
  35
  36 static spte_t *spte_addr(struct lguest *lg, spgd_t spgd, unsigned long vaddr)
  37 {
  38         spte_t *page = __va(spgd.pfn << PAGE_SHIFT);
  39         BUG_ON(!(spgd.flags & _PAGE_PRESENT));
  40         return &page[(vaddr >> PAGE_SHIFT) % PTES_PER_PAGE];
  41 }
  42
  43 /* These access the guest versions. */
  44 static unsigned long gpgd_addr(struct lguest *lg, unsigned long vaddr)
  45 {
  46         unsigned int index = vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT);
  47         return lg->pgdirs[lg->pgdidx].cr3 + index * sizeof(gpgd_t);
  48 }
  49
  50 static unsigned long gpte_addr(struct lguest *lg,
  51                                gpgd_t gpgd, unsigned long vaddr)
  52 {
  53         unsigned long gpage = gpgd.pfn << PAGE_SHIFT;
  54         BUG_ON(!(gpgd.flags & _PAGE_PRESENT));
  55         return gpage + ((vaddr>>PAGE_SHIFT) % PTES_PER_PAGE) * sizeof(gpte_t);
  56 }
  57
  58 /* Do a virtual -> physical mapping on a user page. */
  59 static unsigned long get_pfn(unsigned long virtpfn, int write)
  60 {
  61         struct page *page;
  62         unsigned long ret = -1UL;
  63
  64         down_read(&current->mm->mmap_sem);
  65         if (get_user_pages(current, current->mm, virtpfn << PAGE_SHIFT,
  66                            1, write, 1, &page, NULL) == 1)
  67                 ret = page_to_pfn(page);
  68         up_read(&current->mm->mmap_sem);
  69         return ret;
  70 }
  71
  72 static spte_t gpte_to_spte(struct lguest *lg, gpte_t gpte, int write)
  73 {
  74         spte_t spte;
  75         unsigned long pfn;
  76
  77         /* We ignore the global flag. */
  78         spte.flags = (gpte.flags & ~_PAGE_GLOBAL);
  79         pfn = get_pfn(gpte.pfn, write);
  80         if (pfn == -1UL) {
  81                 kill_guest(lg, "failed to get page %u", gpte.pfn);
  82                 /* Must not put_page() bogus page on cleanup. */
  83                 spte.flags = 0;
  84         }
  85         spte.pfn = pfn;
  86         return spte;
  87 }
  88
  89 static void release_pte(spte_t pte)
  90 {
  91         if (pte.flags & _PAGE_PRESENT)
  92                 put_page(pfn_to_page(pte.pfn));
  93 }
  94
  95 static void check_gpte(struct lguest *lg, gpte_t gpte)
  96 {
  97         if ((gpte.flags & (_PAGE_PWT|_PAGE_PSE)) || gpte.pfn >= lg->pfn_limit)
  98                 kill_guest(lg, "bad page table entry");
  99 }
 100
 101 static void check_gpgd(struct lguest *lg, gpgd_t gpgd)
 102 {
 103         if ((gpgd.flags & ~_PAGE_TABLE) || gpgd.pfn >= lg->pfn_limit)
 104                 kill_guest(lg, "bad page directory entry");
 105 }
 106
 107 /* FIXME: We hold reference to pages, which prevents them from being
 108    swapped.  It'd be nice to have a callback when Linux wants to swap out. */
 109
 110 /* We fault pages in, which allows us to update accessed/dirty bits.
 111  * Return true if we got page. */
 112 int demand_page(struct lguest *lg, unsigned long vaddr, int errcode)
 113 {
 114         gpgd_t gpgd;
 115         spgd_t *spgd;
 116         unsigned long gpte_ptr;
 117         gpte_t gpte;
 118         spte_t *spte;
 119
 120         gpgd = mkgpgd(lgread_u32(lg, gpgd_addr(lg, vaddr)));
 121         if (!(gpgd.flags & _PAGE_PRESENT))
 122                 return 0;
 123
 124         spgd = spgd_addr(lg, lg->pgdidx, vaddr);
 125         if (!(spgd->flags & _PAGE_PRESENT)) {
 126                 /* Get a page of PTEs for them. */
 127                 unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
 128                 /* FIXME: Steal from self in this case? */
 129                 if (!ptepage) {
 130                         kill_guest(lg, "out of memory allocating pte page");
 131                         return 0;
 132                 }
 133                 check_gpgd(lg, gpgd);
 134                 spgd->raw.val = (__pa(ptepage) | gpgd.flags);
 135         }
 136
 137         gpte_ptr = gpte_addr(lg, gpgd, vaddr);
 138         gpte = mkgpte(lgread_u32(lg, gpte_ptr));
 139
 140         /* No page? */
 141         if (!(gpte.flags & _PAGE_PRESENT))
 142                 return 0;
 143
 144         /* Write to read-only page? */
 145         if ((errcode & 2) && !(gpte.flags & _PAGE_RW))
 146                 return 0;
 147
 148         /* User access to a non-user page? */
 149         if ((errcode & 4) && !(gpte.flags & _PAGE_USER))
 150                 return 0;
 151
 152         check_gpte(lg, gpte);
 153         gpte.flags |= _PAGE_ACCESSED;
 154         if (errcode & 2)
 155                 gpte.flags |= _PAGE_DIRTY;
 156
 157         /* We're done with the old pte. */
 158         spte = spte_addr(lg, *spgd, vaddr);
 159         release_pte(*spte);
 160
 161         /* We don't make it writable if this isn't a write: later
 162          * write will fault so we can set dirty bit in guest. */
 163         if (gpte.flags & _PAGE_DIRTY)
 164                 *spte = gpte_to_spte(lg, gpte, 1);
 165         else {
 166                 gpte_t ro_gpte = gpte;
 167                 ro_gpte.flags &= ~_PAGE_RW;
 168                 *spte = gpte_to_spte(lg, ro_gpte, 0);
 169         }
 170
 171         /* Now we update dirty/accessed on guest. */
 172         lgwrite_u32(lg, gpte_ptr, gpte.raw.val);
 173         return 1;
 174 }
 175
 176 /* This is much faster than the full demand_page logic. */
 177 static int page_writable(struct lguest *lg, unsigned long vaddr)
 178 {
 179         spgd_t *spgd;
 180         unsigned long flags;
 181
 182         spgd = spgd_addr(lg, lg->pgdidx, vaddr);
 183         if (!(spgd->flags & _PAGE_PRESENT))
 184                 return 0;
 185
 186         flags = spte_addr(lg, *spgd, vaddr)->flags;
 187         return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
 188 }
 189
 190 void pin_page(struct lguest *lg, unsigned long vaddr)
 191 {
 192         if (!page_writable(lg, vaddr) && !demand_page(lg, vaddr, 2))
 193                 kill_guest(lg, "bad stack page %#lx", vaddr);
 194 }
 195
 196 static void release_pgd(struct lguest *lg, spgd_t *spgd)
 197 {
 198         if (spgd->flags & _PAGE_PRESENT) {
 199                 unsigned int i;
 200                 spte_t *ptepage = __va(spgd->pfn << PAGE_SHIFT);
 201                 for (i = 0; i < PTES_PER_PAGE; i++)
 202                         release_pte(ptepage[i]);
 203                 free_page((long)ptepage);
 204                 spgd->raw.val = 0;
 205         }
 206 }
 207
 208 static void flush_user_mappings(struct lguest *lg, int idx)
 209 {
 210         unsigned int i;
 211         for (i = 0; i < vaddr_to_pgd_index(lg->page_offset); i++)
 212                 release_pgd(lg, lg->pgdirs[idx].pgdir + i);
 213 }
 214
 215 void guest_pagetable_flush_user(struct lguest *lg)
 216 {
 217         flush_user_mappings(lg, lg->pgdidx);
 218 }
 219
 220 static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
 221 {
 222         unsigned int i;
 223         for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
 224                 if (lg->pgdirs[i].cr3 == pgtable)
 225                         break;
 226         return i;
 227 }
 228
 229 static unsigned int new_pgdir(struct lguest *lg,
 230                               unsigned long cr3,
 231                               int *blank_pgdir)
 232 {
 233         unsigned int next;
 234
 235         next = random32() % ARRAY_SIZE(lg->pgdirs);
 236         if (!lg->pgdirs[next].pgdir) {
 237                 lg->pgdirs[next].pgdir = (spgd_t *)get_zeroed_page(GFP_KERNEL);
 238                 if (!lg->pgdirs[next].pgdir)
 239                         next = lg->pgdidx;
 240                 else
 241                         /* There are no mappings: you'll need to re-pin */
 242                         *blank_pgdir = 1;
 243         }
 244         lg->pgdirs[next].cr3 = cr3;
 245         /* Release all the non-kernel mappings. */
 246         flush_user_mappings(lg, next);
 247
 248         return next;
 249 }
 250
 251 void guest_new_pagetable(struct lguest *lg, unsigned long pgtable)
 252 {
 253         int newpgdir, repin = 0;
 254
 255         newpgdir = find_pgdir(lg, pgtable);
 256         if (newpgdir == ARRAY_SIZE(lg->pgdirs))
 257                 newpgdir = new_pgdir(lg, pgtable, &repin);
 258         lg->pgdidx = newpgdir;
 259         if (repin)
 260                 pin_stack_pages(lg);
 261 }
 262
 263 static void release_all_pagetables(struct lguest *lg)
 264 {
 265         unsigned int i, j;
 266
 267         for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
 268                 if (lg->pgdirs[i].pgdir)
 269                         for (j = 0; j < SWITCHER_PGD_INDEX; j++)
 270                                 release_pgd(lg, lg->pgdirs[i].pgdir + j);
 271 }
 272
 273 void guest_pagetable_clear_all(struct lguest *lg)
 274 {
 275         release_all_pagetables(lg);
 276         pin_stack_pages(lg);
 277 }
 278
 279 static void do_set_pte(struct lguest *lg, int idx,
 280                        unsigned long vaddr, gpte_t gpte)
 281 {
 282         spgd_t *spgd = spgd_addr(lg, idx, vaddr);
 283         if (spgd->flags & _PAGE_PRESENT) {
 284                 spte_t *spte = spte_addr(lg, *spgd, vaddr);
 285                 release_pte(*spte);
 286                 if (gpte.flags & (_PAGE_DIRTY | _PAGE_ACCESSED)) {
 287                         check_gpte(lg, gpte);
 288                         *spte = gpte_to_spte(lg, gpte, gpte.flags&_PAGE_DIRTY);
 289                 } else
 290                         spte->raw.val = 0;
 291         }
 292 }
 293
 294 void guest_set_pte(struct lguest *lg,
 295                    unsigned long cr3, unsigned long vaddr, gpte_t gpte)
 296 {
 297         /* Kernel mappings must be changed on all top levels. */
 298         if (vaddr >= lg->page_offset) {
 299                 unsigned int i;
 300                 for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
 301                         if (lg->pgdirs[i].pgdir)
 302                                 do_set_pte(lg, i, vaddr, gpte);
 303         } else {
 304                 int pgdir = find_pgdir(lg, cr3);
 305                 if (pgdir != ARRAY_SIZE(lg->pgdirs))
 306                         do_set_pte(lg, pgdir, vaddr, gpte);
 307         }
 308 }
 309
 310 void guest_set_pmd(struct lguest *lg, unsigned long cr3, u32 idx)
 311 {
 312         int pgdir;
 313
 314         if (idx >= SWITCHER_PGD_INDEX)
 315                 return;
 316
 317         pgdir = find_pgdir(lg, cr3);
 318         if (pgdir < ARRAY_SIZE(lg->pgdirs))
 319                 release_pgd(lg, lg->pgdirs[pgdir].pgdir + idx);
 320 }
 321
 322 int init_guest_pagetable(struct lguest *lg, unsigned long pgtable)
 323 {
 324         /* We assume this in flush_user_mappings, so check now */
 325         if (vaddr_to_pgd_index(lg->page_offset) >= SWITCHER_PGD_INDEX)
 326                 return -EINVAL;
 327         lg->pgdidx = 0;
 328         lg->pgdirs[lg->pgdidx].cr3 = pgtable;
 329         lg->pgdirs[lg->pgdidx].pgdir = (spgd_t*)get_zeroed_page(GFP_KERNEL);
 330         if (!lg->pgdirs[lg->pgdidx].pgdir)
 331                 return -ENOMEM;
 332         return 0;
 333 }
 334
 335 void free_guest_pagetable(struct lguest *lg)
 336 {
 337         unsigned int i;
 338
 339         release_all_pagetables(lg);
 340         for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
 341                 free_page((long)lg->pgdirs[i].pgdir);
 342 }
 343
 344 /* Caller must be preempt-safe */
 345 void map_switcher_in_guest(struct lguest *lg, struct lguest_pages *pages)
 346 {
 347         spte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages);
 348         spgd_t switcher_pgd;
 349         spte_t regs_pte;
 350
 351         /* Since switcher less that 4MB, we simply mug top pte page. */
 352         switcher_pgd.pfn = __pa(switcher_pte_page) >> PAGE_SHIFT;
 353         switcher_pgd.flags = _PAGE_KERNEL;
 354         lg->pgdirs[lg->pgdidx].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd;
 355
 356         /* Map our regs page over stack page. */
 357         regs_pte.pfn = __pa(lg->regs_page) >> PAGE_SHIFT;
 358         regs_pte.flags = _PAGE_KERNEL;
 359         switcher_pte_page[(unsigned long)pages/PAGE_SIZE%PTES_PER_PAGE]
 360                 = regs_pte;
 361 }
 362
 363 static void free_switcher_pte_pages(void)
 364 {
 365         unsigned int i;
 366
 367         for_each_possible_cpu(i)
 368                 free_page((long)switcher_pte_page(i));
 369 }
 370
 371 static __init void populate_switcher_pte_page(unsigned int cpu,
 372                                               struct page *switcher_page[],
 373                                               unsigned int pages)
 374 {
 375         unsigned int i;
 376         spte_t *pte = switcher_pte_page(cpu);
 377
 378         for (i = 0; i < pages; i++) {
 379                 pte[i].pfn = page_to_pfn(switcher_page[i]);
 380                 pte[i].flags = _PAGE_PRESENT|_PAGE_ACCESSED;
 381         }
 382
 383         /* We only map this CPU's pages, so guest can't see others. */
 384         i = pages + cpu*2;
 385
 386         /* First page (regs) is rw, second (state) is ro. */
 387         pte[i].pfn = page_to_pfn(switcher_page[i]);
 388         pte[i].flags = _PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW;
 389         pte[i+1].pfn = page_to_pfn(switcher_page[i+1]);
 390         pte[i+1].flags = _PAGE_PRESENT|_PAGE_ACCESSED;
 391 }
 392
 393 __init int init_pagetables(struct page **switcher_page, unsigned int pages)
 394 {
 395         unsigned int i;
 396
 397         for_each_possible_cpu(i) {
 398                 switcher_pte_page(i) = (spte_t *)get_zeroed_page(GFP_KERNEL);
 399                 if (!switcher_pte_page(i)) {
 400                         free_switcher_pte_pages();
 401                         return -ENOMEM;
 402                 }
 403                 populate_switcher_pte_page(i, switcher_page, pages);
 404         }
 405         return 0;
 406 }
 407
 408 void free_pagetables(void)
 409 {
 410         free_switcher_pte_pages();
 411 }