1 /*P:700
2 * The pagetable code, on the other hand, still shows the scars of
3 * previous encounters. It's functional, and as neat as it can be in the
4 * circumstances, but be wary, for these things are subtle and break easily.
5 * The Guest provides a virtual to physical mapping, but we can neither trust
6 * it nor use it: we verify and convert it here then point the CPU to the
7 * converted Guest pages when running the Guest.
8 :*/
9
10 /* Copyright (C) Rusty Russell IBM Corporation 2013.
11 * GPL v2 and any later version */
12 #include <linux/mm.h>
13 #include <linux/gfp.h>
14 #include <linux/types.h>
15 #include <linux/spinlock.h>
16 #include <linux/random.h>
17 #include <linux/percpu.h>
18 #include <asm/tlbflush.h>
19 #include <asm/uaccess.h>
20 #include "lg.h"
21
22 /*M:008
23 * We hold reference to pages, which prevents them from being swapped.
24 * It'd be nice to have a callback in the "struct mm_struct" when Linux wants
25 * to swap out. If we had this, and a shrinker callback to trim PTE pages, we
26 * could probably consider launching Guests as non-root.
27 :*/
28
29 /*H:300
30 * The Page Table Code
31 *
32 * We use two-level page tables for the Guest, or three-level with PAE. If
33 * you're not entirely comfortable with virtual addresses, physical addresses
34 * and page tables then I recommend you review arch/x86/lguest/boot.c's "Page
35 * Table Handling" (with diagrams!).
36 *
37 * The Guest keeps page tables, but we maintain the actual ones here: these are
38 * called "shadow" page tables. Which is a very Guest-centric name: these are
39 * the real page tables the CPU uses, although we keep them up to date to
40 * reflect the Guest's. (See what I mean about weird naming? Since when do
41 * shadows reflect anything?)
42 *
43 * Anyway, this is the most complicated part of the Host code. There are seven
44 * parts to this:
45 * (i) Looking up a page table entry when the Guest faults,
46 * (ii) Making sure the Guest stack is mapped,
47 * (iii) Setting up a page table entry when the Guest tells us one has changed,
48 * (iv) Switching page tables,
49 * (v) Flushing (throwing away) page tables,
50 * (vi) Mapping the Switcher when the Guest is about to run,
51 * (vii) Setting up the page tables initially.
52 :*/
53
54 /*
55 * The Switcher uses the complete top PTE page. That's 1024 PTE entries (4MB)
56 * or 512 PTE entries with PAE (2MB).
57 */
58 #define SWITCHER_PGD_INDEX (PTRS_PER_PGD - 1)
59
60 /*
61 * For PAE we need the PMD index as well. We use the last 2MB, so we
62 * will need the last pmd entry of the last pmd page.
63 */
64 #ifdef CONFIG_X86_PAE
65 #define CHECK_GPGD_MASK _PAGE_PRESENT
66 #else
67 #define CHECK_GPGD_MASK _PAGE_TABLE
68 #endif
69
70 /*H:320
71 * The page table code is curly enough to need helper functions to keep it
72 * clear and clean. The kernel itself provides many of them; one advantage
73 * of insisting that the Guest and Host use the same CONFIG_X86_PAE setting.
74 *
75 * There are two functions which return pointers to the shadow (aka "real")
76 * page tables.
77 *
78 * spgd_addr() takes the virtual address and returns a pointer to the top-level
79 * page directory entry (PGD) for that address. Since we keep track of several
80 * page tables, the "i" argument tells us which one we're interested in (it's
81 * usually the current one).
82 */
spgd_addr(struct lg_cpu * cpu,u32 i,unsigned long vaddr)83 static pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr)
84 {
85 unsigned int index = pgd_index(vaddr);
86
87 /* Return a pointer index'th pgd entry for the i'th page table. */
88 return &cpu->lg->pgdirs[i].pgdir[index];
89 }
90
91 #ifdef CONFIG_X86_PAE
92 /*
93 * This routine then takes the PGD entry given above, which contains the
94 * address of the PMD page. It then returns a pointer to the PMD entry for the
95 * given address.
96 */
spmd_addr(struct lg_cpu * cpu,pgd_t spgd,unsigned long vaddr)97 static pmd_t *spmd_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
98 {
99 unsigned int index = pmd_index(vaddr);
100 pmd_t *page;
101
102 /* You should never call this if the PGD entry wasn't valid */
103 BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
104 page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
105
106 return &page[index];
107 }
108 #endif
109
110 /*
111 * This routine then takes the page directory entry returned above, which
112 * contains the address of the page table entry (PTE) page. It then returns a
113 * pointer to the PTE entry for the given address.
114 */
spte_addr(struct lg_cpu * cpu,pgd_t spgd,unsigned long vaddr)115 static pte_t *spte_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
116 {
117 #ifdef CONFIG_X86_PAE
118 pmd_t *pmd = spmd_addr(cpu, spgd, vaddr);
119 pte_t *page = __va(pmd_pfn(*pmd) << PAGE_SHIFT);
120
121 /* You should never call this if the PMD entry wasn't valid */
122 BUG_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT));
123 #else
124 pte_t *page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
125 /* You should never call this if the PGD entry wasn't valid */
126 BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
127 #endif
128
129 return &page[pte_index(vaddr)];
130 }
131
132 /*
133 * These functions are just like the above, except they access the Guest
134 * page tables. Hence they return a Guest address.
135 */
gpgd_addr(struct lg_cpu * cpu,unsigned long vaddr)136 static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr)
137 {
138 unsigned int index = vaddr >> (PGDIR_SHIFT);
139 return cpu->lg->pgdirs[cpu->cpu_pgd].gpgdir + index * sizeof(pgd_t);
140 }
141
142 #ifdef CONFIG_X86_PAE
143 /* Follow the PGD to the PMD. */
gpmd_addr(pgd_t gpgd,unsigned long vaddr)144 static unsigned long gpmd_addr(pgd_t gpgd, unsigned long vaddr)
145 {
146 unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
147 BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
148 return gpage + pmd_index(vaddr) * sizeof(pmd_t);
149 }
150
151 /* Follow the PMD to the PTE. */
gpte_addr(struct lg_cpu * cpu,pmd_t gpmd,unsigned long vaddr)152 static unsigned long gpte_addr(struct lg_cpu *cpu,
153 pmd_t gpmd, unsigned long vaddr)
154 {
155 unsigned long gpage = pmd_pfn(gpmd) << PAGE_SHIFT;
156
157 BUG_ON(!(pmd_flags(gpmd) & _PAGE_PRESENT));
158 return gpage + pte_index(vaddr) * sizeof(pte_t);
159 }
160 #else
161 /* Follow the PGD to the PTE (no mid-level for !PAE). */
gpte_addr(struct lg_cpu * cpu,pgd_t gpgd,unsigned long vaddr)162 static unsigned long gpte_addr(struct lg_cpu *cpu,
163 pgd_t gpgd, unsigned long vaddr)
164 {
165 unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
166
167 BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
168 return gpage + pte_index(vaddr) * sizeof(pte_t);
169 }
170 #endif
171 /*:*/
172
173 /*M:007
174 * get_pfn is slow: we could probably try to grab batches of pages here as
175 * an optimization (ie. pre-faulting).
176 :*/
177
178 /*H:350
179 * This routine takes a page number given by the Guest and converts it to
180 * an actual, physical page number. It can fail for several reasons: the
181 * virtual address might not be mapped by the Launcher, the write flag is set
182 * and the page is read-only, or the write flag was set and the page was
183 * shared so had to be copied, but we ran out of memory.
184 *
185 * This holds a reference to the page, so release_pte() is careful to put that
186 * back.
187 */
get_pfn(unsigned long virtpfn,int write)188 static unsigned long get_pfn(unsigned long virtpfn, int write)
189 {
190 struct page *page;
191
192 /* gup me one page at this address please! */
193 if (get_user_pages_fast(virtpfn << PAGE_SHIFT, 1, write, &page) == 1)
194 return page_to_pfn(page);
195
196 /* This value indicates failure. */
197 return -1UL;
198 }
199
200 /*H:340
201 * Converting a Guest page table entry to a shadow (ie. real) page table
202 * entry can be a little tricky. The flags are (almost) the same, but the
203 * Guest PTE contains a virtual page number: the CPU needs the real page
204 * number.
205 */
gpte_to_spte(struct lg_cpu * cpu,pte_t gpte,int write)206 static pte_t gpte_to_spte(struct lg_cpu *cpu, pte_t gpte, int write)
207 {
208 unsigned long pfn, base, flags;
209
210 /*
211 * The Guest sets the global flag, because it thinks that it is using
212 * PGE. We only told it to use PGE so it would tell us whether it was
213 * flushing a kernel mapping or a userspace mapping. We don't actually
214 * use the global bit, so throw it away.
215 */
216 flags = (pte_flags(gpte) & ~_PAGE_GLOBAL);
217
218 /* The Guest's pages are offset inside the Launcher. */
219 base = (unsigned long)cpu->lg->mem_base / PAGE_SIZE;
220
221 /*
222 * We need a temporary "unsigned long" variable to hold the answer from
223 * get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't
224 * fit in spte.pfn. get_pfn() finds the real physical number of the
225 * page, given the virtual number.
226 */
227 pfn = get_pfn(base + pte_pfn(gpte), write);
228 if (pfn == -1UL) {
229 kill_guest(cpu, "failed to get page %lu", pte_pfn(gpte));
230 /*
231 * When we destroy the Guest, we'll go through the shadow page
232 * tables and release_pte() them. Make sure we don't think
233 * this one is valid!
234 */
235 flags = 0;
236 }
237 /* Now we assemble our shadow PTE from the page number and flags. */
238 return pfn_pte(pfn, __pgprot(flags));
239 }
240
241 /*H:460 And to complete the chain, release_pte() looks like this: */
release_pte(pte_t pte)242 static void release_pte(pte_t pte)
243 {
244 /*
245 * Remember that get_user_pages_fast() took a reference to the page, in
246 * get_pfn()? We have to put it back now.
247 */
248 if (pte_flags(pte) & _PAGE_PRESENT)
249 put_page(pte_page(pte));
250 }
251 /*:*/
252
gpte_in_iomem(struct lg_cpu * cpu,pte_t gpte)253 static bool gpte_in_iomem(struct lg_cpu *cpu, pte_t gpte)
254 {
255 /* We don't handle large pages. */
256 if (pte_flags(gpte) & _PAGE_PSE)
257 return false;
258
259 return (pte_pfn(gpte) >= cpu->lg->pfn_limit
260 && pte_pfn(gpte) < cpu->lg->device_limit);
261 }
262
check_gpte(struct lg_cpu * cpu,pte_t gpte)263 static bool check_gpte(struct lg_cpu *cpu, pte_t gpte)
264 {
265 if ((pte_flags(gpte) & _PAGE_PSE) ||
266 pte_pfn(gpte) >= cpu->lg->pfn_limit) {
267 kill_guest(cpu, "bad page table entry");
268 return false;
269 }
270 return true;
271 }
272
check_gpgd(struct lg_cpu * cpu,pgd_t gpgd)273 static bool check_gpgd(struct lg_cpu *cpu, pgd_t gpgd)
274 {
275 if ((pgd_flags(gpgd) & ~CHECK_GPGD_MASK) ||
276 (pgd_pfn(gpgd) >= cpu->lg->pfn_limit)) {
277 kill_guest(cpu, "bad page directory entry");
278 return false;
279 }
280 return true;
281 }
282
283 #ifdef CONFIG_X86_PAE
check_gpmd(struct lg_cpu * cpu,pmd_t gpmd)284 static bool check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
285 {
286 if ((pmd_flags(gpmd) & ~_PAGE_TABLE) ||
287 (pmd_pfn(gpmd) >= cpu->lg->pfn_limit)) {
288 kill_guest(cpu, "bad page middle directory entry");
289 return false;
290 }
291 return true;
292 }
293 #endif
294
295 /*H:331
296 * This is the core routine to walk the shadow page tables and find the page
297 * table entry for a specific address.
298 *
299 * If allocate is set, then we allocate any missing levels, setting the flags
300 * on the new page directory and mid-level directories using the arguments
301 * (which are copied from the Guest's page table entries).
302 */
find_spte(struct lg_cpu * cpu,unsigned long vaddr,bool allocate,int pgd_flags,int pmd_flags)303 static pte_t *find_spte(struct lg_cpu *cpu, unsigned long vaddr, bool allocate,
304 int pgd_flags, int pmd_flags)
305 {
306 pgd_t *spgd;
307 /* Mid level for PAE. */
308 #ifdef CONFIG_X86_PAE
309 pmd_t *spmd;
310 #endif
311
312 /* Get top level entry. */
313 spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
314 if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) {
315 /* No shadow entry: allocate a new shadow PTE page. */
316 unsigned long ptepage;
317
318 /* If they didn't want us to allocate anything, stop. */
319 if (!allocate)
320 return NULL;
321
322 ptepage = get_zeroed_page(GFP_KERNEL);
323 /*
324 * This is not really the Guest's fault, but killing it is
325 * simple for this corner case.
326 */
327 if (!ptepage) {
328 kill_guest(cpu, "out of memory allocating pte page");
329 return NULL;
330 }
331 /*
332 * And we copy the flags to the shadow PGD entry. The page
333 * number in the shadow PGD is the page we just allocated.
334 */
335 set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags));
336 }
337
338 /*
339 * Intel's Physical Address Extension actually uses three levels of
340 * page tables, so we need to look in the mid-level.
341 */
342 #ifdef CONFIG_X86_PAE
343 /* Now look at the mid-level shadow entry. */
344 spmd = spmd_addr(cpu, *spgd, vaddr);
345
346 if (!(pmd_flags(*spmd) & _PAGE_PRESENT)) {
347 /* No shadow entry: allocate a new shadow PTE page. */
348 unsigned long ptepage;
349
350 /* If they didn't want us to allocate anything, stop. */
351 if (!allocate)
352 return NULL;
353
354 ptepage = get_zeroed_page(GFP_KERNEL);
355
356 /*
357 * This is not really the Guest's fault, but killing it is
358 * simple for this corner case.
359 */
360 if (!ptepage) {
361 kill_guest(cpu, "out of memory allocating pmd page");
362 return NULL;
363 }
364
365 /*
366 * And we copy the flags to the shadow PMD entry. The page
367 * number in the shadow PMD is the page we just allocated.
368 */
369 set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags));
370 }
371 #endif
372
373 /* Get the pointer to the shadow PTE entry we're going to set. */
374 return spte_addr(cpu, *spgd, vaddr);
375 }
376
377 /*H:330
378 * (i) Looking up a page table entry when the Guest faults.
379 *
380 * We saw this call in run_guest(): when we see a page fault in the Guest, we
381 * come here. That's because we only set up the shadow page tables lazily as
382 * they're needed, so we get page faults all the time and quietly fix them up
383 * and return to the Guest without it knowing.
384 *
385 * If we fixed up the fault (ie. we mapped the address), this routine returns
386 * true. Otherwise, it was a real fault and we need to tell the Guest.
387 *
388 * There's a corner case: they're trying to access memory between
389 * pfn_limit and device_limit, which is I/O memory. In this case, we
390 * return false and set @iomem to the physical address, so the the
391 * Launcher can handle the instruction manually.
392 */
demand_page(struct lg_cpu * cpu,unsigned long vaddr,int errcode,unsigned long * iomem)393 bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode,
394 unsigned long *iomem)
395 {
396 unsigned long gpte_ptr;
397 pte_t gpte;
398 pte_t *spte;
399 pmd_t gpmd;
400 pgd_t gpgd;
401
402 *iomem = 0;
403
404 /* We never demand page the Switcher, so trying is a mistake. */
405 if (vaddr >= switcher_addr)
406 return false;
407
408 /* First step: get the top-level Guest page table entry. */
409 if (unlikely(cpu->linear_pages)) {
410 /* Faking up a linear mapping. */
411 gpgd = __pgd(CHECK_GPGD_MASK);
412 } else {
413 gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
414 /* Toplevel not present? We can't map it in. */
415 if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
416 return false;
417
418 /*
419 * This kills the Guest if it has weird flags or tries to
420 * refer to a "physical" address outside the bounds.
421 */
422 if (!check_gpgd(cpu, gpgd))
423 return false;
424 }
425
426 /* This "mid-level" entry is only used for non-linear, PAE mode. */
427 gpmd = __pmd(_PAGE_TABLE);
428
429 #ifdef CONFIG_X86_PAE
430 if (likely(!cpu->linear_pages)) {
431 gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
432 /* Middle level not present? We can't map it in. */
433 if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
434 return false;
435
436 /*
437 * This kills the Guest if it has weird flags or tries to
438 * refer to a "physical" address outside the bounds.
439 */
440 if (!check_gpmd(cpu, gpmd))
441 return false;
442 }
443
444 /*
445 * OK, now we look at the lower level in the Guest page table: keep its
446 * address, because we might update it later.
447 */
448 gpte_ptr = gpte_addr(cpu, gpmd, vaddr);
449 #else
450 /*
451 * OK, now we look at the lower level in the Guest page table: keep its
452 * address, because we might update it later.
453 */
454 gpte_ptr = gpte_addr(cpu, gpgd, vaddr);
455 #endif
456
457 if (unlikely(cpu->linear_pages)) {
458 /* Linear? Make up a PTE which points to same page. */
459 gpte = __pte((vaddr & PAGE_MASK) | _PAGE_RW | _PAGE_PRESENT);
460 } else {
461 /* Read the actual PTE value. */
462 gpte = lgread(cpu, gpte_ptr, pte_t);
463 }
464
465 /* If this page isn't in the Guest page tables, we can't page it in. */
466 if (!(pte_flags(gpte) & _PAGE_PRESENT))
467 return false;
468
469 /*
470 * Check they're not trying to write to a page the Guest wants
471 * read-only (bit 2 of errcode == write).
472 */
473 if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW))
474 return false;
475
476 /* User access to a kernel-only page? (bit 3 == user access) */
477 if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER))
478 return false;
479
480 /* If they're accessing io memory, we expect a fault. */
481 if (gpte_in_iomem(cpu, gpte)) {
482 *iomem = (pte_pfn(gpte) << PAGE_SHIFT) | (vaddr & ~PAGE_MASK);
483 return false;
484 }
485
486 /*
487 * Check that the Guest PTE flags are OK, and the page number is below
488 * the pfn_limit (ie. not mapping the Launcher binary).
489 */
490 if (!check_gpte(cpu, gpte))
491 return false;
492
493 /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
494 gpte = pte_mkyoung(gpte);
495 if (errcode & 2)
496 gpte = pte_mkdirty(gpte);
497
498 /* Get the pointer to the shadow PTE entry we're going to set. */
499 spte = find_spte(cpu, vaddr, true, pgd_flags(gpgd), pmd_flags(gpmd));
500 if (!spte)
501 return false;
502
503 /*
504 * If there was a valid shadow PTE entry here before, we release it.
505 * This can happen with a write to a previously read-only entry.
506 */
507 release_pte(*spte);
508
509 /*
510 * If this is a write, we insist that the Guest page is writable (the
511 * final arg to gpte_to_spte()).
512 */
513 if (pte_dirty(gpte))
514 *spte = gpte_to_spte(cpu, gpte, 1);
515 else
516 /*
517 * If this is a read, don't set the "writable" bit in the page
518 * table entry, even if the Guest says it's writable. That way
519 * we will come back here when a write does actually occur, so
520 * we can update the Guest's _PAGE_DIRTY flag.
521 */
522 set_pte(spte, gpte_to_spte(cpu, pte_wrprotect(gpte), 0));
523
524 /*
525 * Finally, we write the Guest PTE entry back: we've set the
526 * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags.
527 */
528 if (likely(!cpu->linear_pages))
529 lgwrite(cpu, gpte_ptr, pte_t, gpte);
530
531 /*
532 * The fault is fixed, the page table is populated, the mapping
533 * manipulated, the result returned and the code complete. A small
534 * delay and a trace of alliteration are the only indications the Guest
535 * has that a page fault occurred at all.
536 */
537 return true;
538 }
539
540 /*H:360
541 * (ii) Making sure the Guest stack is mapped.
542 *
543 * Remember that direct traps into the Guest need a mapped Guest kernel stack.
544 * pin_stack_pages() calls us here: we could simply call demand_page(), but as
545 * we've seen that logic is quite long, and usually the stack pages are already
546 * mapped, so it's overkill.
547 *
548 * This is a quick version which answers the question: is this virtual address
549 * mapped by the shadow page tables, and is it writable?
550 */
page_writable(struct lg_cpu * cpu,unsigned long vaddr)551 static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr)
552 {
553 pte_t *spte;
554 unsigned long flags;
555
556 /* You can't put your stack in the Switcher! */
557 if (vaddr >= switcher_addr)
558 return false;
559
560 /* If there's no shadow PTE, it's not writable. */
561 spte = find_spte(cpu, vaddr, false, 0, 0);
562 if (!spte)
563 return false;
564
565 /*
566 * Check the flags on the pte entry itself: it must be present and
567 * writable.
568 */
569 flags = pte_flags(*spte);
570 return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
571 }
572
573 /*
574 * So, when pin_stack_pages() asks us to pin a page, we check if it's already
575 * in the page tables, and if not, we call demand_page() with error code 2
576 * (meaning "write").
577 */
pin_page(struct lg_cpu * cpu,unsigned long vaddr)578 void pin_page(struct lg_cpu *cpu, unsigned long vaddr)
579 {
580 unsigned long iomem;
581
582 if (!page_writable(cpu, vaddr) && !demand_page(cpu, vaddr, 2, &iomem))
583 kill_guest(cpu, "bad stack page %#lx", vaddr);
584 }
585 /*:*/
586
587 #ifdef CONFIG_X86_PAE
release_pmd(pmd_t * spmd)588 static void release_pmd(pmd_t *spmd)
589 {
590 /* If the entry's not present, there's nothing to release. */
591 if (pmd_flags(*spmd) & _PAGE_PRESENT) {
592 unsigned int i;
593 pte_t *ptepage = __va(pmd_pfn(*spmd) << PAGE_SHIFT);
594 /* For each entry in the page, we might need to release it. */
595 for (i = 0; i < PTRS_PER_PTE; i++)
596 release_pte(ptepage[i]);
597 /* Now we can free the page of PTEs */
598 free_page((long)ptepage);
599 /* And zero out the PMD entry so we never release it twice. */
600 set_pmd(spmd, __pmd(0));
601 }
602 }
603
release_pgd(pgd_t * spgd)604 static void release_pgd(pgd_t *spgd)
605 {
606 /* If the entry's not present, there's nothing to release. */
607 if (pgd_flags(*spgd) & _PAGE_PRESENT) {
608 unsigned int i;
609 pmd_t *pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
610
611 for (i = 0; i < PTRS_PER_PMD; i++)
612 release_pmd(&pmdpage[i]);
613
614 /* Now we can free the page of PMDs */
615 free_page((long)pmdpage);
616 /* And zero out the PGD entry so we never release it twice. */
617 set_pgd(spgd, __pgd(0));
618 }
619 }
620
621 #else /* !CONFIG_X86_PAE */
622 /*H:450
623 * If we chase down the release_pgd() code, the non-PAE version looks like
624 * this. The PAE version is almost identical, but instead of calling
625 * release_pte it calls release_pmd(), which looks much like this.
626 */
release_pgd(pgd_t * spgd)627 static void release_pgd(pgd_t *spgd)
628 {
629 /* If the entry's not present, there's nothing to release. */
630 if (pgd_flags(*spgd) & _PAGE_PRESENT) {
631 unsigned int i;
632 /*
633 * Converting the pfn to find the actual PTE page is easy: turn
634 * the page number into a physical address, then convert to a
635 * virtual address (easy for kernel pages like this one).
636 */
637 pte_t *ptepage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
638 /* For each entry in the page, we might need to release it. */
639 for (i = 0; i < PTRS_PER_PTE; i++)
640 release_pte(ptepage[i]);
641 /* Now we can free the page of PTEs */
642 free_page((long)ptepage);
643 /* And zero out the PGD entry so we never release it twice. */
644 *spgd = __pgd(0);
645 }
646 }
647 #endif
648
649 /*H:445
650 * We saw flush_user_mappings() twice: once from the flush_user_mappings()
651 * hypercall and once in new_pgdir() when we re-used a top-level pgdir page.
652 * It simply releases every PTE page from 0 up to the Guest's kernel address.
653 */
flush_user_mappings(struct lguest * lg,int idx)654 static void flush_user_mappings(struct lguest *lg, int idx)
655 {
656 unsigned int i;
657 /* Release every pgd entry up to the kernel's address. */
658 for (i = 0; i < pgd_index(lg->kernel_address); i++)
659 release_pgd(lg->pgdirs[idx].pgdir + i);
660 }
661
662 /*H:440
663 * (v) Flushing (throwing away) page tables,
664 *
665 * The Guest has a hypercall to throw away the page tables: it's used when a
666 * large number of mappings have been changed.
667 */
guest_pagetable_flush_user(struct lg_cpu * cpu)668 void guest_pagetable_flush_user(struct lg_cpu *cpu)
669 {
670 /* Drop the userspace part of the current page table. */
671 flush_user_mappings(cpu->lg, cpu->cpu_pgd);
672 }
673 /*:*/
674
675 /* We walk down the guest page tables to get a guest-physical address */
__guest_pa(struct lg_cpu * cpu,unsigned long vaddr,unsigned long * paddr)676 bool __guest_pa(struct lg_cpu *cpu, unsigned long vaddr, unsigned long *paddr)
677 {
678 pgd_t gpgd;
679 pte_t gpte;
680 #ifdef CONFIG_X86_PAE
681 pmd_t gpmd;
682 #endif
683
684 /* Still not set up? Just map 1:1. */
685 if (unlikely(cpu->linear_pages)) {
686 *paddr = vaddr;
687 return true;
688 }
689
690 /* First step: get the top-level Guest page table entry. */
691 gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
692 /* Toplevel not present? We can't map it in. */
693 if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
694 goto fail;
695
696 #ifdef CONFIG_X86_PAE
697 gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
698 if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
699 goto fail;
700 gpte = lgread(cpu, gpte_addr(cpu, gpmd, vaddr), pte_t);
701 #else
702 gpte = lgread(cpu, gpte_addr(cpu, gpgd, vaddr), pte_t);
703 #endif
704 if (!(pte_flags(gpte) & _PAGE_PRESENT))
705 goto fail;
706
707 *paddr = pte_pfn(gpte) * PAGE_SIZE | (vaddr & ~PAGE_MASK);
708 return true;
709
710 fail:
711 *paddr = -1UL;
712 return false;
713 }
714
715 /*
716 * This is the version we normally use: kills the Guest if it uses a
717 * bad address
718 */
guest_pa(struct lg_cpu * cpu,unsigned long vaddr)719 unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr)
720 {
721 unsigned long paddr;
722
723 if (!__guest_pa(cpu, vaddr, &paddr))
724 kill_guest(cpu, "Bad address %#lx", vaddr);
725 return paddr;
726 }
727
728 /*
729 * We keep several page tables. This is a simple routine to find the page
730 * table (if any) corresponding to this top-level address the Guest has given
731 * us.
732 */
find_pgdir(struct lguest * lg,unsigned long pgtable)733 static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
734 {
735 unsigned int i;
736 for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
737 if (lg->pgdirs[i].pgdir && lg->pgdirs[i].gpgdir == pgtable)
738 break;
739 return i;
740 }
741
742 /*H:435
743 * And this is us, creating the new page directory. If we really do
744 * allocate a new one (and so the kernel parts are not there), we set
745 * blank_pgdir.
746 */
new_pgdir(struct lg_cpu * cpu,unsigned long gpgdir,int * blank_pgdir)747 static unsigned int new_pgdir(struct lg_cpu *cpu,
748 unsigned long gpgdir,
749 int *blank_pgdir)
750 {
751 unsigned int next;
752
753 /*
754 * We pick one entry at random to throw out. Choosing the Least
755 * Recently Used might be better, but this is easy.
756 */
757 next = prandom_u32() % ARRAY_SIZE(cpu->lg->pgdirs);
758 /* If it's never been allocated at all before, try now. */
759 if (!cpu->lg->pgdirs[next].pgdir) {
760 cpu->lg->pgdirs[next].pgdir =
761 (pgd_t *)get_zeroed_page(GFP_KERNEL);
762 /* If the allocation fails, just keep using the one we have */
763 if (!cpu->lg->pgdirs[next].pgdir)
764 next = cpu->cpu_pgd;
765 else {
766 /*
767 * This is a blank page, so there are no kernel
768 * mappings: caller must map the stack!
769 */
770 *blank_pgdir = 1;
771 }
772 }
773 /* Record which Guest toplevel this shadows. */
774 cpu->lg->pgdirs[next].gpgdir = gpgdir;
775 /* Release all the non-kernel mappings. */
776 flush_user_mappings(cpu->lg, next);
777
778 /* This hasn't run on any CPU at all. */
779 cpu->lg->pgdirs[next].last_host_cpu = -1;
780
781 return next;
782 }
783
784 /*H:501
785 * We do need the Switcher code mapped at all times, so we allocate that
786 * part of the Guest page table here. We map the Switcher code immediately,
787 * but defer mapping of the guest register page and IDT/LDT etc page until
788 * just before we run the guest in map_switcher_in_guest().
789 *
790 * We *could* do this setup in map_switcher_in_guest(), but at that point
791 * we've interrupts disabled, and allocating pages like that is fraught: we
792 * can't sleep if we need to free up some memory.
793 */
allocate_switcher_mapping(struct lg_cpu * cpu)794 static bool allocate_switcher_mapping(struct lg_cpu *cpu)
795 {
796 int i;
797
798 for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
799 pte_t *pte = find_spte(cpu, switcher_addr + i * PAGE_SIZE, true,
800 CHECK_GPGD_MASK, _PAGE_TABLE);
801 if (!pte)
802 return false;
803
804 /*
805 * Map the switcher page if not already there. It might
806 * already be there because we call allocate_switcher_mapping()
807 * in guest_set_pgd() just in case it did discard our Switcher
808 * mapping, but it probably didn't.
809 */
810 if (i == 0 && !(pte_flags(*pte) & _PAGE_PRESENT)) {
811 /* Get a reference to the Switcher page. */
812 get_page(lg_switcher_pages[0]);
813 /* Create a read-only, exectuable, kernel-style PTE */
814 set_pte(pte,
815 mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX));
816 }
817 }
818 cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped = true;
819 return true;
820 }
821
822 /*H:470
823 * Finally, a routine which throws away everything: all PGD entries in all
824 * the shadow page tables, including the Guest's kernel mappings. This is used
825 * when we destroy the Guest.
826 */
release_all_pagetables(struct lguest * lg)827 static void release_all_pagetables(struct lguest *lg)
828 {
829 unsigned int i, j;
830
831 /* Every shadow pagetable this Guest has */
832 for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) {
833 if (!lg->pgdirs[i].pgdir)
834 continue;
835
836 /* Every PGD entry. */
837 for (j = 0; j < PTRS_PER_PGD; j++)
838 release_pgd(lg->pgdirs[i].pgdir + j);
839 lg->pgdirs[i].switcher_mapped = false;
840 lg->pgdirs[i].last_host_cpu = -1;
841 }
842 }
843
844 /*
845 * We also throw away everything when a Guest tells us it's changed a kernel
846 * mapping. Since kernel mappings are in every page table, it's easiest to
847 * throw them all away. This traps the Guest in amber for a while as
848 * everything faults back in, but it's rare.
849 */
guest_pagetable_clear_all(struct lg_cpu * cpu)850 void guest_pagetable_clear_all(struct lg_cpu *cpu)
851 {
852 release_all_pagetables(cpu->lg);
853 /* We need the Guest kernel stack mapped again. */
854 pin_stack_pages(cpu);
855 /* And we need Switcher allocated. */
856 if (!allocate_switcher_mapping(cpu))
857 kill_guest(cpu, "Cannot populate switcher mapping");
858 }
859
860 /*H:430
861 * (iv) Switching page tables
862 *
863 * Now we've seen all the page table setting and manipulation, let's see
864 * what happens when the Guest changes page tables (ie. changes the top-level
865 * pgdir). This occurs on almost every context switch.
866 */
guest_new_pagetable(struct lg_cpu * cpu,unsigned long pgtable)867 void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
868 {
869 int newpgdir, repin = 0;
870
871 /*
872 * The very first time they call this, we're actually running without
873 * any page tables; we've been making it up. Throw them away now.
874 */
875 if (unlikely(cpu->linear_pages)) {
876 release_all_pagetables(cpu->lg);
877 cpu->linear_pages = false;
878 /* Force allocation of a new pgdir. */
879 newpgdir = ARRAY_SIZE(cpu->lg->pgdirs);
880 } else {
881 /* Look to see if we have this one already. */
882 newpgdir = find_pgdir(cpu->lg, pgtable);
883 }
884
885 /*
886 * If not, we allocate or mug an existing one: if it's a fresh one,
887 * repin gets set to 1.
888 */
889 if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs))
890 newpgdir = new_pgdir(cpu, pgtable, &repin);
891 /* Change the current pgd index to the new one. */
892 cpu->cpu_pgd = newpgdir;
893 /*
894 * If it was completely blank, we map in the Guest kernel stack and
895 * the Switcher.
896 */
897 if (repin)
898 pin_stack_pages(cpu);
899
900 if (!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped) {
901 if (!allocate_switcher_mapping(cpu))
902 kill_guest(cpu, "Cannot populate switcher mapping");
903 }
904 }
905 /*:*/
906
907 /*M:009
908 * Since we throw away all mappings when a kernel mapping changes, our
909 * performance sucks for guests using highmem. In fact, a guest with
910 * PAGE_OFFSET 0xc0000000 (the default) and more than about 700MB of RAM is
911 * usually slower than a Guest with less memory.
912 *
913 * This, of course, cannot be fixed. It would take some kind of... well, I
914 * don't know, but the term "puissant code-fu" comes to mind.
915 :*/
916
917 /*H:420
918 * This is the routine which actually sets the page table entry for then
919 * "idx"'th shadow page table.
920 *
921 * Normally, we can just throw out the old entry and replace it with 0: if they
922 * use it demand_page() will put the new entry in. We need to do this anyway:
923 * The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page
924 * is read from, and _PAGE_DIRTY when it's written to.
925 *
926 * But Avi Kivity pointed out that most Operating Systems (Linux included) set
927 * these bits on PTEs immediately anyway. This is done to save the CPU from
928 * having to update them, but it helps us the same way: if they set
929 * _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if
930 * they set _PAGE_DIRTY then we can put a writable PTE entry in immediately.
931 */
__guest_set_pte(struct lg_cpu * cpu,int idx,unsigned long vaddr,pte_t gpte)932 static void __guest_set_pte(struct lg_cpu *cpu, int idx,
933 unsigned long vaddr, pte_t gpte)
934 {
935 /* Look up the matching shadow page directory entry. */
936 pgd_t *spgd = spgd_addr(cpu, idx, vaddr);
937 #ifdef CONFIG_X86_PAE
938 pmd_t *spmd;
939 #endif
940
941 /* If the top level isn't present, there's no entry to update. */
942 if (pgd_flags(*spgd) & _PAGE_PRESENT) {
943 #ifdef CONFIG_X86_PAE
944 spmd = spmd_addr(cpu, *spgd, vaddr);
945 if (pmd_flags(*spmd) & _PAGE_PRESENT) {
946 #endif
947 /* Otherwise, start by releasing the existing entry. */
948 pte_t *spte = spte_addr(cpu, *spgd, vaddr);
949 release_pte(*spte);
950
951 /*
952 * If they're setting this entry as dirty or accessed,
953 * we might as well put that entry they've given us in
954 * now. This shaves 10% off a copy-on-write
955 * micro-benchmark.
956 */
957 if ((pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED))
958 && !gpte_in_iomem(cpu, gpte)) {
959 if (!check_gpte(cpu, gpte))
960 return;
961 set_pte(spte,
962 gpte_to_spte(cpu, gpte,
963 pte_flags(gpte) & _PAGE_DIRTY));
964 } else {
965 /*
966 * Otherwise kill it and we can demand_page()
967 * it in later.
968 */
969 set_pte(spte, __pte(0));
970 }
971 #ifdef CONFIG_X86_PAE
972 }
973 #endif
974 }
975 }
976
977 /*H:410
978 * Updating a PTE entry is a little trickier.
979 *
980 * We keep track of several different page tables (the Guest uses one for each
981 * process, so it makes sense to cache at least a few). Each of these have
982 * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for
983 * all processes. So when the page table above that address changes, we update
984 * all the page tables, not just the current one. This is rare.
985 *
986 * The benefit is that when we have to track a new page table, we can keep all
987 * the kernel mappings. This speeds up context switch immensely.
988 */
guest_set_pte(struct lg_cpu * cpu,unsigned long gpgdir,unsigned long vaddr,pte_t gpte)989 void guest_set_pte(struct lg_cpu *cpu,
990 unsigned long gpgdir, unsigned long vaddr, pte_t gpte)
991 {
992 /* We don't let you remap the Switcher; we need it to get back! */
993 if (vaddr >= switcher_addr) {
994 kill_guest(cpu, "attempt to set pte into Switcher pages");
995 return;
996 }
997
998 /*
999 * Kernel mappings must be changed on all top levels. Slow, but doesn't
1000 * happen often.
1001 */
1002 if (vaddr >= cpu->lg->kernel_address) {
1003 unsigned int i;
1004 for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++)
1005 if (cpu->lg->pgdirs[i].pgdir)
1006 __guest_set_pte(cpu, i, vaddr, gpte);
1007 } else {
1008 /* Is this page table one we have a shadow for? */
1009 int pgdir = find_pgdir(cpu->lg, gpgdir);
1010 if (pgdir != ARRAY_SIZE(cpu->lg->pgdirs))
1011 /* If so, do the update. */
1012 __guest_set_pte(cpu, pgdir, vaddr, gpte);
1013 }
1014 }
1015
1016 /*H:400
1017 * (iii) Setting up a page table entry when the Guest tells us one has changed.
1018 *
1019 * Just like we did in interrupts_and_traps.c, it makes sense for us to deal
1020 * with the other side of page tables while we're here: what happens when the
1021 * Guest asks for a page table to be updated?
1022 *
1023 * We already saw that demand_page() will fill in the shadow page tables when
1024 * needed, so we can simply remove shadow page table entries whenever the Guest
1025 * tells us they've changed. When the Guest tries to use the new entry it will
1026 * fault and demand_page() will fix it up.
1027 *
1028 * So with that in mind here's our code to update a (top-level) PGD entry:
1029 */
guest_set_pgd(struct lguest * lg,unsigned long gpgdir,u32 idx)1030 void guest_set_pgd(struct lguest *lg, unsigned long gpgdir, u32 idx)
1031 {
1032 int pgdir;
1033
1034 if (idx > PTRS_PER_PGD) {
1035 kill_guest(&lg->cpus[0], "Attempt to set pgd %u/%u",
1036 idx, PTRS_PER_PGD);
1037 return;
1038 }
1039
1040 /* If they're talking about a page table we have a shadow for... */
1041 pgdir = find_pgdir(lg, gpgdir);
1042 if (pgdir < ARRAY_SIZE(lg->pgdirs)) {
1043 /* ... throw it away. */
1044 release_pgd(lg->pgdirs[pgdir].pgdir + idx);
1045 /* That might have been the Switcher mapping, remap it. */
1046 if (!allocate_switcher_mapping(&lg->cpus[0])) {
1047 kill_guest(&lg->cpus[0],
1048 "Cannot populate switcher mapping");
1049 }
1050 lg->pgdirs[pgdir].last_host_cpu = -1;
1051 }
1052 }
1053
1054 #ifdef CONFIG_X86_PAE
1055 /* For setting a mid-level, we just throw everything away. It's easy. */
guest_set_pmd(struct lguest * lg,unsigned long pmdp,u32 idx)1056 void guest_set_pmd(struct lguest *lg, unsigned long pmdp, u32 idx)
1057 {
1058 guest_pagetable_clear_all(&lg->cpus[0]);
1059 }
1060 #endif
1061
1062 /*H:500
1063 * (vii) Setting up the page tables initially.
1064 *
1065 * When a Guest is first created, set initialize a shadow page table which
1066 * we will populate on future faults. The Guest doesn't have any actual
1067 * pagetables yet, so we set linear_pages to tell demand_page() to fake it
1068 * for the moment.
1069 *
1070 * We do need the Switcher to be mapped at all times, so we allocate that
1071 * part of the Guest page table here.
1072 */
init_guest_pagetable(struct lguest * lg)1073 int init_guest_pagetable(struct lguest *lg)
1074 {
1075 struct lg_cpu *cpu = &lg->cpus[0];
1076 int allocated = 0;
1077
1078 /* lg (and lg->cpus[]) starts zeroed: this allocates a new pgdir */
1079 cpu->cpu_pgd = new_pgdir(cpu, 0, &allocated);
1080 if (!allocated)
1081 return -ENOMEM;
1082
1083 /* We start with a linear mapping until the initialize. */
1084 cpu->linear_pages = true;
1085
1086 /* Allocate the page tables for the Switcher. */
1087 if (!allocate_switcher_mapping(cpu)) {
1088 release_all_pagetables(lg);
1089 return -ENOMEM;
1090 }
1091
1092 return 0;
1093 }
1094
1095 /*H:508 When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
page_table_guest_data_init(struct lg_cpu * cpu)1096 void page_table_guest_data_init(struct lg_cpu *cpu)
1097 {
1098 /*
1099 * We tell the Guest that it can't use the virtual addresses
1100 * used by the Switcher. This trick is equivalent to 4GB -
1101 * switcher_addr.
1102 */
1103 u32 top = ~switcher_addr + 1;
1104
1105 /* We get the kernel address: above this is all kernel memory. */
1106 if (get_user(cpu->lg->kernel_address,
1107 &cpu->lg->lguest_data->kernel_address)
1108 /*
1109 * We tell the Guest that it can't use the top virtual
1110 * addresses (used by the Switcher).
1111 */
1112 || put_user(top, &cpu->lg->lguest_data->reserve_mem)) {
1113 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
1114 return;
1115 }
1116
1117 /*
1118 * In flush_user_mappings() we loop from 0 to
1119 * "pgd_index(lg->kernel_address)". This assumes it won't hit the
1120 * Switcher mappings, so check that now.
1121 */
1122 if (cpu->lg->kernel_address >= switcher_addr)
1123 kill_guest(cpu, "bad kernel address %#lx",
1124 cpu->lg->kernel_address);
1125 }
1126
1127 /* When a Guest dies, our cleanup is fairly simple. */
free_guest_pagetable(struct lguest * lg)1128 void free_guest_pagetable(struct lguest *lg)
1129 {
1130 unsigned int i;
1131
1132 /* Throw away all page table pages. */
1133 release_all_pagetables(lg);
1134 /* Now free the top levels: free_page() can handle 0 just fine. */
1135 for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
1136 free_page((long)lg->pgdirs[i].pgdir);
1137 }
1138
1139 /*H:481
1140 * This clears the Switcher mappings for cpu #i.
1141 */
remove_switcher_percpu_map(struct lg_cpu * cpu,unsigned int i)1142 static void remove_switcher_percpu_map(struct lg_cpu *cpu, unsigned int i)
1143 {
1144 unsigned long base = switcher_addr + PAGE_SIZE + i * PAGE_SIZE*2;
1145 pte_t *pte;
1146
1147 /* Clear the mappings for both pages. */
1148 pte = find_spte(cpu, base, false, 0, 0);
1149 release_pte(*pte);
1150 set_pte(pte, __pte(0));
1151
1152 pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
1153 release_pte(*pte);
1154 set_pte(pte, __pte(0));
1155 }
1156
1157 /*H:480
1158 * (vi) Mapping the Switcher when the Guest is about to run.
1159 *
1160 * The Switcher and the two pages for this CPU need to be visible in the Guest
1161 * (and not the pages for other CPUs).
1162 *
1163 * The pages for the pagetables have all been allocated before: we just need
1164 * to make sure the actual PTEs are up-to-date for the CPU we're about to run
1165 * on.
1166 */
map_switcher_in_guest(struct lg_cpu * cpu,struct lguest_pages * pages)1167 void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
1168 {
1169 unsigned long base;
1170 struct page *percpu_switcher_page, *regs_page;
1171 pte_t *pte;
1172 struct pgdir *pgdir = &cpu->lg->pgdirs[cpu->cpu_pgd];
1173
1174 /* Switcher page should always be mapped by now! */
1175 BUG_ON(!pgdir->switcher_mapped);
1176
1177 /*
1178 * Remember that we have two pages for each Host CPU, so we can run a
1179 * Guest on each CPU without them interfering. We need to make sure
1180 * those pages are mapped correctly in the Guest, but since we usually
1181 * run on the same CPU, we cache that, and only update the mappings
1182 * when we move.
1183 */
1184 if (pgdir->last_host_cpu == raw_smp_processor_id())
1185 return;
1186
1187 /* -1 means unknown so we remove everything. */
1188 if (pgdir->last_host_cpu == -1) {
1189 unsigned int i;
1190 for_each_possible_cpu(i)
1191 remove_switcher_percpu_map(cpu, i);
1192 } else {
1193 /* We know exactly what CPU mapping to remove. */
1194 remove_switcher_percpu_map(cpu, pgdir->last_host_cpu);
1195 }
1196
1197 /*
1198 * When we're running the Guest, we want the Guest's "regs" page to
1199 * appear where the first Switcher page for this CPU is. This is an
1200 * optimization: when the Switcher saves the Guest registers, it saves
1201 * them into the first page of this CPU's "struct lguest_pages": if we
1202 * make sure the Guest's register page is already mapped there, we
1203 * don't have to copy them out again.
1204 */
1205 /* Find the shadow PTE for this regs page. */
1206 base = switcher_addr + PAGE_SIZE
1207 + raw_smp_processor_id() * sizeof(struct lguest_pages);
1208 pte = find_spte(cpu, base, false, 0, 0);
1209 regs_page = pfn_to_page(__pa(cpu->regs_page) >> PAGE_SHIFT);
1210 get_page(regs_page);
1211 set_pte(pte, mk_pte(regs_page, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL)));
1212
1213 /*
1214 * We map the second page of the struct lguest_pages read-only in
1215 * the Guest: the IDT, GDT and other things it's not supposed to
1216 * change.
1217 */
1218 pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
1219 percpu_switcher_page
1220 = lg_switcher_pages[1 + raw_smp_processor_id()*2 + 1];
1221 get_page(percpu_switcher_page);
1222 set_pte(pte, mk_pte(percpu_switcher_page,
1223 __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL)));
1224
1225 pgdir->last_host_cpu = raw_smp_processor_id();
1226 }
1227
1228 /*H:490
1229 * We've made it through the page table code. Perhaps our tired brains are
1230 * still processing the details, or perhaps we're simply glad it's over.
1231 *
1232 * If nothing else, note that all this complexity in juggling shadow page tables
1233 * in sync with the Guest's page tables is for one reason: for most Guests this
1234 * page table dance determines how bad performance will be. This is why Xen
1235 * uses exotic direct Guest pagetable manipulation, and why both Intel and AMD
1236 * have implemented shadow page table support directly into hardware.
1237 *
1238 * There is just one file remaining in the Host.
1239 */
1240