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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 2006.
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 SWITCHER_PMD_INDEX (PTRS_PER_PMD - 1)
66#define RESERVE_MEM 2U
67#define CHECK_GPGD_MASK _PAGE_PRESENT
68#else
69#define RESERVE_MEM 4U
70#define CHECK_GPGD_MASK _PAGE_TABLE
71#endif
72
73/*
74 * We actually need a separate PTE page for each CPU. Remember that after the
75 * Switcher code itself comes two pages for each CPU, and we don't want this
76 * CPU's guest to see the pages of any other CPU.
77 */
78static DEFINE_PER_CPU(pte_t *, switcher_pte_pages);
79#define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)
80
81/*H:320
82 * The page table code is curly enough to need helper functions to keep it
83 * clear and clean. The kernel itself provides many of them; one advantage
84 * of insisting that the Guest and Host use the same CONFIG_PAE setting.
85 *
86 * There are two functions which return pointers to the shadow (aka "real")
87 * page tables.
88 *
89 * spgd_addr() takes the virtual address and returns a pointer to the top-level
90 * page directory entry (PGD) for that address. Since we keep track of several
91 * page tables, the "i" argument tells us which one we're interested in (it's
92 * usually the current one).
93 */
94static pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr)
95{
96 unsigned int index = pgd_index(vaddr);
97
98#ifndef CONFIG_X86_PAE
99 /* We kill any Guest trying to touch the Switcher addresses. */
100 if (index >= SWITCHER_PGD_INDEX) {
101 kill_guest(cpu, "attempt to access switcher pages");
102 index = 0;
103 }
104#endif
105 /* Return a pointer index'th pgd entry for the i'th page table. */
106 return &cpu->lg->pgdirs[i].pgdir[index];
107}
108
109#ifdef CONFIG_X86_PAE
110/*
111 * This routine then takes the PGD entry given above, which contains the
112 * address of the PMD page. It then returns a pointer to the PMD entry for the
113 * given address.
114 */
115static pmd_t *spmd_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
116{
117 unsigned int index = pmd_index(vaddr);
118 pmd_t *page;
119
120 /* We kill any Guest trying to touch the Switcher addresses. */
121 if (pgd_index(vaddr) == SWITCHER_PGD_INDEX &&
122 index >= SWITCHER_PMD_INDEX) {
123 kill_guest(cpu, "attempt to access switcher pages");
124 index = 0;
125 }
126
127 /* You should never call this if the PGD entry wasn't valid */
128 BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
129 page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
130
131 return &page[index];
132}
133#endif
134
135/*
136 * This routine then takes the page directory entry returned above, which
137 * contains the address of the page table entry (PTE) page. It then returns a
138 * pointer to the PTE entry for the given address.
139 */
140static pte_t *spte_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
141{
142#ifdef CONFIG_X86_PAE
143 pmd_t *pmd = spmd_addr(cpu, spgd, vaddr);
144 pte_t *page = __va(pmd_pfn(*pmd) << PAGE_SHIFT);
145
146 /* You should never call this if the PMD entry wasn't valid */
147 BUG_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT));
148#else
149 pte_t *page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
150 /* You should never call this if the PGD entry wasn't valid */
151 BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
152#endif
153
154 return &page[pte_index(vaddr)];
155}
156
157/*
158 * These functions are just like the above, except they access the Guest
159 * page tables. Hence they return a Guest address.
160 */
161static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr)
162{
163 unsigned int index = vaddr >> (PGDIR_SHIFT);
164 return cpu->lg->pgdirs[cpu->cpu_pgd].gpgdir + index * sizeof(pgd_t);
165}
166
167#ifdef CONFIG_X86_PAE
168/* Follow the PGD to the PMD. */
169static unsigned long gpmd_addr(pgd_t gpgd, unsigned long vaddr)
170{
171 unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
172 BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
173 return gpage + pmd_index(vaddr) * sizeof(pmd_t);
174}
175
176/* Follow the PMD to the PTE. */
177static unsigned long gpte_addr(struct lg_cpu *cpu,
178 pmd_t gpmd, unsigned long vaddr)
179{
180 unsigned long gpage = pmd_pfn(gpmd) << PAGE_SHIFT;
181
182 BUG_ON(!(pmd_flags(gpmd) & _PAGE_PRESENT));
183 return gpage + pte_index(vaddr) * sizeof(pte_t);
184}
185#else
186/* Follow the PGD to the PTE (no mid-level for !PAE). */
187static unsigned long gpte_addr(struct lg_cpu *cpu,
188 pgd_t gpgd, unsigned long vaddr)
189{
190 unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
191
192 BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
193 return gpage + pte_index(vaddr) * sizeof(pte_t);
194}
195#endif
196/*:*/
197
198/*M:007
199 * get_pfn is slow: we could probably try to grab batches of pages here as
200 * an optimization (ie. pre-faulting).
201:*/
202
203/*H:350
204 * This routine takes a page number given by the Guest and converts it to
205 * an actual, physical page number. It can fail for several reasons: the
206 * virtual address might not be mapped by the Launcher, the write flag is set
207 * and the page is read-only, or the write flag was set and the page was
208 * shared so had to be copied, but we ran out of memory.
209 *
210 * This holds a reference to the page, so release_pte() is careful to put that
211 * back.
212 */
213static unsigned long get_pfn(unsigned long virtpfn, int write)
214{
215 struct page *page;
216
217 /* gup me one page at this address please! */
218 if (get_user_pages_fast(virtpfn << PAGE_SHIFT, 1, write, &page) == 1)
219 return page_to_pfn(page);
220
221 /* This value indicates failure. */
222 return -1UL;
223}
224
225/*H:340
226 * Converting a Guest page table entry to a shadow (ie. real) page table
227 * entry can be a little tricky. The flags are (almost) the same, but the
228 * Guest PTE contains a virtual page number: the CPU needs the real page
229 * number.
230 */
231static pte_t gpte_to_spte(struct lg_cpu *cpu, pte_t gpte, int write)
232{
233 unsigned long pfn, base, flags;
234
235 /*
236 * The Guest sets the global flag, because it thinks that it is using
237 * PGE. We only told it to use PGE so it would tell us whether it was
238 * flushing a kernel mapping or a userspace mapping. We don't actually
239 * use the global bit, so throw it away.
240 */
241 flags = (pte_flags(gpte) & ~_PAGE_GLOBAL);
242
243 /* The Guest's pages are offset inside the Launcher. */
244 base = (unsigned long)cpu->lg->mem_base / PAGE_SIZE;
245
246 /*
247 * We need a temporary "unsigned long" variable to hold the answer from
248 * get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't
249 * fit in spte.pfn. get_pfn() finds the real physical number of the
250 * page, given the virtual number.
251 */
252 pfn = get_pfn(base + pte_pfn(gpte), write);
253 if (pfn == -1UL) {
254 kill_guest(cpu, "failed to get page %lu", pte_pfn(gpte));
255 /*
256 * When we destroy the Guest, we'll go through the shadow page
257 * tables and release_pte() them. Make sure we don't think
258 * this one is valid!
259 */
260 flags = 0;
261 }
262 /* Now we assemble our shadow PTE from the page number and flags. */
263 return pfn_pte(pfn, __pgprot(flags));
264}
265
266/*H:460 And to complete the chain, release_pte() looks like this: */
267static void release_pte(pte_t pte)
268{
269 /*
270 * Remember that get_user_pages_fast() took a reference to the page, in
271 * get_pfn()? We have to put it back now.
272 */
273 if (pte_flags(pte) & _PAGE_PRESENT)
274 put_page(pte_page(pte));
275}
276/*:*/
277
278static void check_gpte(struct lg_cpu *cpu, pte_t gpte)
279{
280 if ((pte_flags(gpte) & _PAGE_PSE) ||
281 pte_pfn(gpte) >= cpu->lg->pfn_limit)
282 kill_guest(cpu, "bad page table entry");
283}
284
285static void check_gpgd(struct lg_cpu *cpu, pgd_t gpgd)
286{
287 if ((pgd_flags(gpgd) & ~CHECK_GPGD_MASK) ||
288 (pgd_pfn(gpgd) >= cpu->lg->pfn_limit))
289 kill_guest(cpu, "bad page directory entry");
290}
291
292#ifdef CONFIG_X86_PAE
293static void check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
294{
295 if ((pmd_flags(gpmd) & ~_PAGE_TABLE) ||
296 (pmd_pfn(gpmd) >= cpu->lg->pfn_limit))
297 kill_guest(cpu, "bad page middle directory entry");
298}
299#endif
300
301/*H:330
302 * (i) Looking up a page table entry when the Guest faults.
303 *
304 * We saw this call in run_guest(): when we see a page fault in the Guest, we
305 * come here. That's because we only set up the shadow page tables lazily as
306 * they're needed, so we get page faults all the time and quietly fix them up
307 * and return to the Guest without it knowing.
308 *
309 * If we fixed up the fault (ie. we mapped the address), this routine returns
310 * true. Otherwise, it was a real fault and we need to tell the Guest.
311 */
312bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
313{
314 pgd_t gpgd;
315 pgd_t *spgd;
316 unsigned long gpte_ptr;
317 pte_t gpte;
318 pte_t *spte;
319
320 /* Mid level for PAE. */
321#ifdef CONFIG_X86_PAE
322 pmd_t *spmd;
323 pmd_t gpmd;
324#endif
325
326 /* First step: get the top-level Guest page table entry. */
327 if (unlikely(cpu->linear_pages)) {
328 /* Faking up a linear mapping. */
329 gpgd = __pgd(CHECK_GPGD_MASK);
330 } else {
331 gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
332 /* Toplevel not present? We can't map it in. */
333 if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
334 return false;
335 }
336
337 /* Now look at the matching shadow entry. */
338 spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
339 if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) {
340 /* No shadow entry: allocate a new shadow PTE page. */
341 unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
342 /*
343 * This is not really the Guest's fault, but killing it is
344 * simple for this corner case.
345 */
346 if (!ptepage) {
347 kill_guest(cpu, "out of memory allocating pte page");
348 return false;
349 }
350 /* We check that the Guest pgd is OK. */
351 check_gpgd(cpu, gpgd);
352 /*
353 * And we copy the flags to the shadow PGD entry. The page
354 * number in the shadow PGD is the page we just allocated.
355 */
356 set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags(gpgd)));
357 }
358
359#ifdef CONFIG_X86_PAE
360 if (unlikely(cpu->linear_pages)) {
361 /* Faking up a linear mapping. */
362 gpmd = __pmd(_PAGE_TABLE);
363 } else {
364 gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
365 /* Middle level not present? We can't map it in. */
366 if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
367 return false;
368 }
369
370 /* Now look at the matching shadow entry. */
371 spmd = spmd_addr(cpu, *spgd, vaddr);
372
373 if (!(pmd_flags(*spmd) & _PAGE_PRESENT)) {
374 /* No shadow entry: allocate a new shadow PTE page. */
375 unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
376
377 /*
378 * This is not really the Guest's fault, but killing it is
379 * simple for this corner case.
380 */
381 if (!ptepage) {
382 kill_guest(cpu, "out of memory allocating pte page");
383 return false;
384 }
385
386 /* We check that the Guest pmd is OK. */
387 check_gpmd(cpu, gpmd);
388
389 /*
390 * And we copy the flags to the shadow PMD entry. The page
391 * number in the shadow PMD is the page we just allocated.
392 */
393 set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags(gpmd)));
394 }
395
396 /*
397 * OK, now we look at the lower level in the Guest page table: keep its
398 * address, because we might update it later.
399 */
400 gpte_ptr = gpte_addr(cpu, gpmd, vaddr);
401#else
402 /*
403 * OK, now we look at the lower level in the Guest page table: keep its
404 * address, because we might update it later.
405 */
406 gpte_ptr = gpte_addr(cpu, gpgd, vaddr);
407#endif
408
409 if (unlikely(cpu->linear_pages)) {
410 /* Linear? Make up a PTE which points to same page. */
411 gpte = __pte((vaddr & PAGE_MASK) | _PAGE_RW | _PAGE_PRESENT);
412 } else {
413 /* Read the actual PTE value. */
414 gpte = lgread(cpu, gpte_ptr, pte_t);
415 }
416
417 /* If this page isn't in the Guest page tables, we can't page it in. */
418 if (!(pte_flags(gpte) & _PAGE_PRESENT))
419 return false;
420
421 /*
422 * Check they're not trying to write to a page the Guest wants
423 * read-only (bit 2 of errcode == write).
424 */
425 if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW))
426 return false;
427
428 /* User access to a kernel-only page? (bit 3 == user access) */
429 if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER))
430 return false;
431
432 /*
433 * Check that the Guest PTE flags are OK, and the page number is below
434 * the pfn_limit (ie. not mapping the Launcher binary).
435 */
436 check_gpte(cpu, gpte);
437
438 /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
439 gpte = pte_mkyoung(gpte);
440 if (errcode & 2)
441 gpte = pte_mkdirty(gpte);
442
443 /* Get the pointer to the shadow PTE entry we're going to set. */
444 spte = spte_addr(cpu, *spgd, vaddr);
445
446 /*
447 * If there was a valid shadow PTE entry here before, we release it.
448 * This can happen with a write to a previously read-only entry.
449 */
450 release_pte(*spte);
451
452 /*
453 * If this is a write, we insist that the Guest page is writable (the
454 * final arg to gpte_to_spte()).
455 */
456 if (pte_dirty(gpte))
457 *spte = gpte_to_spte(cpu, gpte, 1);
458 else
459 /*
460 * If this is a read, don't set the "writable" bit in the page
461 * table entry, even if the Guest says it's writable. That way
462 * we will come back here when a write does actually occur, so
463 * we can update the Guest's _PAGE_DIRTY flag.
464 */
465 set_pte(spte, gpte_to_spte(cpu, pte_wrprotect(gpte), 0));
466
467 /*
468 * Finally, we write the Guest PTE entry back: we've set the
469 * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags.
470 */
471 if (likely(!cpu->linear_pages))
472 lgwrite(cpu, gpte_ptr, pte_t, gpte);
473
474 /*
475 * The fault is fixed, the page table is populated, the mapping
476 * manipulated, the result returned and the code complete. A small
477 * delay and a trace of alliteration are the only indications the Guest
478 * has that a page fault occurred at all.
479 */
480 return true;
481}
482
483/*H:360
484 * (ii) Making sure the Guest stack is mapped.
485 *
486 * Remember that direct traps into the Guest need a mapped Guest kernel stack.
487 * pin_stack_pages() calls us here: we could simply call demand_page(), but as
488 * we've seen that logic is quite long, and usually the stack pages are already
489 * mapped, so it's overkill.
490 *
491 * This is a quick version which answers the question: is this virtual address
492 * mapped by the shadow page tables, and is it writable?
493 */
494static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr)
495{
496 pgd_t *spgd;
497 unsigned long flags;
498
499#ifdef CONFIG_X86_PAE
500 pmd_t *spmd;
501#endif
502 /* Look at the current top level entry: is it present? */
503 spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
504 if (!(pgd_flags(*spgd) & _PAGE_PRESENT))
505 return false;
506
507#ifdef CONFIG_X86_PAE
508 spmd = spmd_addr(cpu, *spgd, vaddr);
509 if (!(pmd_flags(*spmd) & _PAGE_PRESENT))
510 return false;
511#endif
512
513 /*
514 * Check the flags on the pte entry itself: it must be present and
515 * writable.
516 */
517 flags = pte_flags(*(spte_addr(cpu, *spgd, vaddr)));
518
519 return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
520}
521
522/*
523 * So, when pin_stack_pages() asks us to pin a page, we check if it's already
524 * in the page tables, and if not, we call demand_page() with error code 2
525 * (meaning "write").
526 */
527void pin_page(struct lg_cpu *cpu, unsigned long vaddr)
528{
529 if (!page_writable(cpu, vaddr) && !demand_page(cpu, vaddr, 2))
530 kill_guest(cpu, "bad stack page %#lx", vaddr);
531}
532/*:*/
533
534#ifdef CONFIG_X86_PAE
535static void release_pmd(pmd_t *spmd)
536{
537 /* If the entry's not present, there's nothing to release. */
538 if (pmd_flags(*spmd) & _PAGE_PRESENT) {
539 unsigned int i;
540 pte_t *ptepage = __va(pmd_pfn(*spmd) << PAGE_SHIFT);
541 /* For each entry in the page, we might need to release it. */
542 for (i = 0; i < PTRS_PER_PTE; i++)
543 release_pte(ptepage[i]);
544 /* Now we can free the page of PTEs */
545 free_page((long)ptepage);
546 /* And zero out the PMD entry so we never release it twice. */
547 set_pmd(spmd, __pmd(0));
548 }
549}
550
551static void release_pgd(pgd_t *spgd)
552{
553 /* If the entry's not present, there's nothing to release. */
554 if (pgd_flags(*spgd) & _PAGE_PRESENT) {
555 unsigned int i;
556 pmd_t *pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
557
558 for (i = 0; i < PTRS_PER_PMD; i++)
559 release_pmd(&pmdpage[i]);
560
561 /* Now we can free the page of PMDs */
562 free_page((long)pmdpage);
563 /* And zero out the PGD entry so we never release it twice. */
564 set_pgd(spgd, __pgd(0));
565 }
566}
567
568#else /* !CONFIG_X86_PAE */
569/*H:450
570 * If we chase down the release_pgd() code, the non-PAE version looks like
571 * this. The PAE version is almost identical, but instead of calling
572 * release_pte it calls release_pmd(), which looks much like this.
573 */
574static void release_pgd(pgd_t *spgd)
575{
576 /* If the entry's not present, there's nothing to release. */
577 if (pgd_flags(*spgd) & _PAGE_PRESENT) {
578 unsigned int i;
579 /*
580 * Converting the pfn to find the actual PTE page is easy: turn
581 * the page number into a physical address, then convert to a
582 * virtual address (easy for kernel pages like this one).
583 */
584 pte_t *ptepage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
585 /* For each entry in the page, we might need to release it. */
586 for (i = 0; i < PTRS_PER_PTE; i++)
587 release_pte(ptepage[i]);
588 /* Now we can free the page of PTEs */
589 free_page((long)ptepage);
590 /* And zero out the PGD entry so we never release it twice. */
591 *spgd = __pgd(0);
592 }
593}
594#endif
595
596/*H:445
597 * We saw flush_user_mappings() twice: once from the flush_user_mappings()
598 * hypercall and once in new_pgdir() when we re-used a top-level pgdir page.
599 * It simply releases every PTE page from 0 up to the Guest's kernel address.
600 */
601static void flush_user_mappings(struct lguest *lg, int idx)
602{
603 unsigned int i;
604 /* Release every pgd entry up to the kernel's address. */
605 for (i = 0; i < pgd_index(lg->kernel_address); i++)
606 release_pgd(lg->pgdirs[idx].pgdir + i);
607}
608
609/*H:440
610 * (v) Flushing (throwing away) page tables,
611 *
612 * The Guest has a hypercall to throw away the page tables: it's used when a
613 * large number of mappings have been changed.
614 */
615void guest_pagetable_flush_user(struct lg_cpu *cpu)
616{
617 /* Drop the userspace part of the current page table. */
618 flush_user_mappings(cpu->lg, cpu->cpu_pgd);
619}
620/*:*/
621
622/* We walk down the guest page tables to get a guest-physical address */
623unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr)
624{
625 pgd_t gpgd;
626 pte_t gpte;
627#ifdef CONFIG_X86_PAE
628 pmd_t gpmd;
629#endif
630
631 /* Still not set up? Just map 1:1. */
632 if (unlikely(cpu->linear_pages))
633 return vaddr;
634
635 /* First step: get the top-level Guest page table entry. */
636 gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
637 /* Toplevel not present? We can't map it in. */
638 if (!(pgd_flags(gpgd) & _PAGE_PRESENT)) {
639 kill_guest(cpu, "Bad address %#lx", vaddr);
640 return -1UL;
641 }
642
643#ifdef CONFIG_X86_PAE
644 gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
645 if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
646 kill_guest(cpu, "Bad address %#lx", vaddr);
647 gpte = lgread(cpu, gpte_addr(cpu, gpmd, vaddr), pte_t);
648#else
649 gpte = lgread(cpu, gpte_addr(cpu, gpgd, vaddr), pte_t);
650#endif
651 if (!(pte_flags(gpte) & _PAGE_PRESENT))
652 kill_guest(cpu, "Bad address %#lx", vaddr);
653
654 return pte_pfn(gpte) * PAGE_SIZE | (vaddr & ~PAGE_MASK);
655}
656
657/*
658 * We keep several page tables. This is a simple routine to find the page
659 * table (if any) corresponding to this top-level address the Guest has given
660 * us.
661 */
662static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
663{
664 unsigned int i;
665 for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
666 if (lg->pgdirs[i].pgdir && lg->pgdirs[i].gpgdir == pgtable)
667 break;
668 return i;
669}
670
671/*H:435
672 * And this is us, creating the new page directory. If we really do
673 * allocate a new one (and so the kernel parts are not there), we set
674 * blank_pgdir.
675 */
676static unsigned int new_pgdir(struct lg_cpu *cpu,
677 unsigned long gpgdir,
678 int *blank_pgdir)
679{
680 unsigned int next;
681#ifdef CONFIG_X86_PAE
682 pmd_t *pmd_table;
683#endif
684
685 /*
686 * We pick one entry at random to throw out. Choosing the Least
687 * Recently Used might be better, but this is easy.
688 */
689 next = random32() % ARRAY_SIZE(cpu->lg->pgdirs);
690 /* If it's never been allocated at all before, try now. */
691 if (!cpu->lg->pgdirs[next].pgdir) {
692 cpu->lg->pgdirs[next].pgdir =
693 (pgd_t *)get_zeroed_page(GFP_KERNEL);
694 /* If the allocation fails, just keep using the one we have */
695 if (!cpu->lg->pgdirs[next].pgdir)
696 next = cpu->cpu_pgd;
697 else {
698#ifdef CONFIG_X86_PAE
699 /*
700 * In PAE mode, allocate a pmd page and populate the
701 * last pgd entry.
702 */
703 pmd_table = (pmd_t *)get_zeroed_page(GFP_KERNEL);
704 if (!pmd_table) {
705 free_page((long)cpu->lg->pgdirs[next].pgdir);
706 set_pgd(cpu->lg->pgdirs[next].pgdir, __pgd(0));
707 next = cpu->cpu_pgd;
708 } else {
709 set_pgd(cpu->lg->pgdirs[next].pgdir +
710 SWITCHER_PGD_INDEX,
711 __pgd(__pa(pmd_table) | _PAGE_PRESENT));
712 /*
713 * This is a blank page, so there are no kernel
714 * mappings: caller must map the stack!
715 */
716 *blank_pgdir = 1;
717 }
718#else
719 *blank_pgdir = 1;
720#endif
721 }
722 }
723 /* Record which Guest toplevel this shadows. */
724 cpu->lg->pgdirs[next].gpgdir = gpgdir;
725 /* Release all the non-kernel mappings. */
726 flush_user_mappings(cpu->lg, next);
727
728 return next;
729}
730
731/*H:470
732 * Finally, a routine which throws away everything: all PGD entries in all
733 * the shadow page tables, including the Guest's kernel mappings. This is used
734 * when we destroy the Guest.
735 */
736static void release_all_pagetables(struct lguest *lg)
737{
738 unsigned int i, j;
739
740 /* Every shadow pagetable this Guest has */
741 for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
742 if (lg->pgdirs[i].pgdir) {
743#ifdef CONFIG_X86_PAE
744 pgd_t *spgd;
745 pmd_t *pmdpage;
746 unsigned int k;
747
748 /* Get the last pmd page. */
749 spgd = lg->pgdirs[i].pgdir + SWITCHER_PGD_INDEX;
750 pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
751
752 /*
753 * And release the pmd entries of that pmd page,
754 * except for the switcher pmd.
755 */
756 for (k = 0; k < SWITCHER_PMD_INDEX; k++)
757 release_pmd(&pmdpage[k]);
758#endif
759 /* Every PGD entry except the Switcher at the top */
760 for (j = 0; j < SWITCHER_PGD_INDEX; j++)
761 release_pgd(lg->pgdirs[i].pgdir + j);
762 }
763}
764
765/*
766 * We also throw away everything when a Guest tells us it's changed a kernel
767 * mapping. Since kernel mappings are in every page table, it's easiest to
768 * throw them all away. This traps the Guest in amber for a while as
769 * everything faults back in, but it's rare.
770 */
771void guest_pagetable_clear_all(struct lg_cpu *cpu)
772{
773 release_all_pagetables(cpu->lg);
774 /* We need the Guest kernel stack mapped again. */
775 pin_stack_pages(cpu);
776}
777
778/*H:430
779 * (iv) Switching page tables
780 *
781 * Now we've seen all the page table setting and manipulation, let's see
782 * what happens when the Guest changes page tables (ie. changes the top-level
783 * pgdir). This occurs on almost every context switch.
784 */
785void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
786{
787 int newpgdir, repin = 0;
788
789 /*
790 * The very first time they call this, we're actually running without
791 * any page tables; we've been making it up. Throw them away now.
792 */
793 if (unlikely(cpu->linear_pages)) {
794 release_all_pagetables(cpu->lg);
795 cpu->linear_pages = false;
796 /* Force allocation of a new pgdir. */
797 newpgdir = ARRAY_SIZE(cpu->lg->pgdirs);
798 } else {
799 /* Look to see if we have this one already. */
800 newpgdir = find_pgdir(cpu->lg, pgtable);
801 }
802
803 /*
804 * If not, we allocate or mug an existing one: if it's a fresh one,
805 * repin gets set to 1.
806 */
807 if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs))
808 newpgdir = new_pgdir(cpu, pgtable, &repin);
809 /* Change the current pgd index to the new one. */
810 cpu->cpu_pgd = newpgdir;
811 /* If it was completely blank, we map in the Guest kernel stack */
812 if (repin)
813 pin_stack_pages(cpu);
814}
815/*:*/
816
817/*M:009
818 * Since we throw away all mappings when a kernel mapping changes, our
819 * performance sucks for guests using highmem. In fact, a guest with
820 * PAGE_OFFSET 0xc0000000 (the default) and more than about 700MB of RAM is
821 * usually slower than a Guest with less memory.
822 *
823 * This, of course, cannot be fixed. It would take some kind of... well, I
824 * don't know, but the term "puissant code-fu" comes to mind.
825:*/
826
827/*H:420
828 * This is the routine which actually sets the page table entry for then
829 * "idx"'th shadow page table.
830 *
831 * Normally, we can just throw out the old entry and replace it with 0: if they
832 * use it demand_page() will put the new entry in. We need to do this anyway:
833 * The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page
834 * is read from, and _PAGE_DIRTY when it's written to.
835 *
836 * But Avi Kivity pointed out that most Operating Systems (Linux included) set
837 * these bits on PTEs immediately anyway. This is done to save the CPU from
838 * having to update them, but it helps us the same way: if they set
839 * _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if
840 * they set _PAGE_DIRTY then we can put a writable PTE entry in immediately.
841 */
842static void do_set_pte(struct lg_cpu *cpu, int idx,
843 unsigned long vaddr, pte_t gpte)
844{
845 /* Look up the matching shadow page directory entry. */
846 pgd_t *spgd = spgd_addr(cpu, idx, vaddr);
847#ifdef CONFIG_X86_PAE
848 pmd_t *spmd;
849#endif
850
851 /* If the top level isn't present, there's no entry to update. */
852 if (pgd_flags(*spgd) & _PAGE_PRESENT) {
853#ifdef CONFIG_X86_PAE
854 spmd = spmd_addr(cpu, *spgd, vaddr);
855 if (pmd_flags(*spmd) & _PAGE_PRESENT) {
856#endif
857 /* Otherwise, start by releasing the existing entry. */
858 pte_t *spte = spte_addr(cpu, *spgd, vaddr);
859 release_pte(*spte);
860
861 /*
862 * If they're setting this entry as dirty or accessed,
863 * we might as well put that entry they've given us in
864 * now. This shaves 10% off a copy-on-write
865 * micro-benchmark.
866 */
867 if (pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED)) {
868 check_gpte(cpu, gpte);
869 set_pte(spte,
870 gpte_to_spte(cpu, gpte,
871 pte_flags(gpte) & _PAGE_DIRTY));
872 } else {
873 /*
874 * Otherwise kill it and we can demand_page()
875 * it in later.
876 */
877 set_pte(spte, __pte(0));
878 }
879#ifdef CONFIG_X86_PAE
880 }
881#endif
882 }
883}
884
885/*H:410
886 * Updating a PTE entry is a little trickier.
887 *
888 * We keep track of several different page tables (the Guest uses one for each
889 * process, so it makes sense to cache at least a few). Each of these have
890 * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for
891 * all processes. So when the page table above that address changes, we update
892 * all the page tables, not just the current one. This is rare.
893 *
894 * The benefit is that when we have to track a new page table, we can keep all
895 * the kernel mappings. This speeds up context switch immensely.
896 */
897void guest_set_pte(struct lg_cpu *cpu,
898 unsigned long gpgdir, unsigned long vaddr, pte_t gpte)
899{
900 /*
901 * Kernel mappings must be changed on all top levels. Slow, but doesn't
902 * happen often.
903 */
904 if (vaddr >= cpu->lg->kernel_address) {
905 unsigned int i;
906 for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++)
907 if (cpu->lg->pgdirs[i].pgdir)
908 do_set_pte(cpu, i, vaddr, gpte);
909 } else {
910 /* Is this page table one we have a shadow for? */
911 int pgdir = find_pgdir(cpu->lg, gpgdir);
912 if (pgdir != ARRAY_SIZE(cpu->lg->pgdirs))
913 /* If so, do the update. */
914 do_set_pte(cpu, pgdir, vaddr, gpte);
915 }
916}
917
918/*H:400
919 * (iii) Setting up a page table entry when the Guest tells us one has changed.
920 *
921 * Just like we did in interrupts_and_traps.c, it makes sense for us to deal
922 * with the other side of page tables while we're here: what happens when the
923 * Guest asks for a page table to be updated?
924 *
925 * We already saw that demand_page() will fill in the shadow page tables when
926 * needed, so we can simply remove shadow page table entries whenever the Guest
927 * tells us they've changed. When the Guest tries to use the new entry it will
928 * fault and demand_page() will fix it up.
929 *
930 * So with that in mind here's our code to update a (top-level) PGD entry:
931 */
932void guest_set_pgd(struct lguest *lg, unsigned long gpgdir, u32 idx)
933{
934 int pgdir;
935
936 if (idx >= SWITCHER_PGD_INDEX)
937 return;
938
939 /* If they're talking about a page table we have a shadow for... */
940 pgdir = find_pgdir(lg, gpgdir);
941 if (pgdir < ARRAY_SIZE(lg->pgdirs))
942 /* ... throw it away. */
943 release_pgd(lg->pgdirs[pgdir].pgdir + idx);
944}
945
946#ifdef CONFIG_X86_PAE
947/* For setting a mid-level, we just throw everything away. It's easy. */
948void guest_set_pmd(struct lguest *lg, unsigned long pmdp, u32 idx)
949{
950 guest_pagetable_clear_all(&lg->cpus[0]);
951}
952#endif
953
954/*H:500
955 * (vii) Setting up the page tables initially.
956 *
957 * When a Guest is first created, set initialize a shadow page table which
958 * we will populate on future faults. The Guest doesn't have any actual
959 * pagetables yet, so we set linear_pages to tell demand_page() to fake it
960 * for the moment.
961 */
962int init_guest_pagetable(struct lguest *lg)
963{
964 struct lg_cpu *cpu = &lg->cpus[0];
965 int allocated = 0;
966
967 /* lg (and lg->cpus[]) starts zeroed: this allocates a new pgdir */
968 cpu->cpu_pgd = new_pgdir(cpu, 0, &allocated);
969 if (!allocated)
970 return -ENOMEM;
971
972 /* We start with a linear mapping until the initialize. */
973 cpu->linear_pages = true;
974 return 0;
975}
976
977/*H:508 When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
978void page_table_guest_data_init(struct lg_cpu *cpu)
979{
980 /* We get the kernel address: above this is all kernel memory. */
981 if (get_user(cpu->lg->kernel_address,
982 &cpu->lg->lguest_data->kernel_address)
983 /*
984 * We tell the Guest that it can't use the top 2 or 4 MB
985 * of virtual addresses used by the Switcher.
986 */
987 || put_user(RESERVE_MEM * 1024 * 1024,
988 &cpu->lg->lguest_data->reserve_mem)) {
989 kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
990 return;
991 }
992
993 /*
994 * In flush_user_mappings() we loop from 0 to
995 * "pgd_index(lg->kernel_address)". This assumes it won't hit the
996 * Switcher mappings, so check that now.
997 */
998#ifdef CONFIG_X86_PAE
999 if (pgd_index(cpu->lg->kernel_address) == SWITCHER_PGD_INDEX &&
1000 pmd_index(cpu->lg->kernel_address) == SWITCHER_PMD_INDEX)
1001#else
1002 if (pgd_index(cpu->lg->kernel_address) >= SWITCHER_PGD_INDEX)
1003#endif
1004 kill_guest(cpu, "bad kernel address %#lx",
1005 cpu->lg->kernel_address);
1006}
1007
1008/* When a Guest dies, our cleanup is fairly simple. */
1009void free_guest_pagetable(struct lguest *lg)
1010{
1011 unsigned int i;
1012
1013 /* Throw away all page table pages. */
1014 release_all_pagetables(lg);
1015 /* Now free the top levels: free_page() can handle 0 just fine. */
1016 for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
1017 free_page((long)lg->pgdirs[i].pgdir);
1018}
1019
1020/*H:480
1021 * (vi) Mapping the Switcher when the Guest is about to run.
1022 *
1023 * The Switcher and the two pages for this CPU need to be visible in the
1024 * Guest (and not the pages for other CPUs). We have the appropriate PTE pages
1025 * for each CPU already set up, we just need to hook them in now we know which
1026 * Guest is about to run on this CPU.
1027 */
1028void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
1029{
1030 pte_t *switcher_pte_page = __this_cpu_read(switcher_pte_pages);
1031 pte_t regs_pte;
1032
1033#ifdef CONFIG_X86_PAE
1034 pmd_t switcher_pmd;
1035 pmd_t *pmd_table;
1036
1037 switcher_pmd = pfn_pmd(__pa(switcher_pte_page) >> PAGE_SHIFT,
1038 PAGE_KERNEL_EXEC);
1039
1040 /* Figure out where the pmd page is, by reading the PGD, and converting
1041 * it to a virtual address. */
1042 pmd_table = __va(pgd_pfn(cpu->lg->
1043 pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX])
1044 << PAGE_SHIFT);
1045 /* Now write it into the shadow page table. */
1046 set_pmd(&pmd_table[SWITCHER_PMD_INDEX], switcher_pmd);
1047#else
1048 pgd_t switcher_pgd;
1049
1050 /*
1051 * Make the last PGD entry for this Guest point to the Switcher's PTE
1052 * page for this CPU (with appropriate flags).
1053 */
1054 switcher_pgd = __pgd(__pa(switcher_pte_page) | __PAGE_KERNEL_EXEC);
1055
1056 cpu->lg->pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd;
1057
1058#endif
1059 /*
1060 * We also change the Switcher PTE page. When we're running the Guest,
1061 * we want the Guest's "regs" page to appear where the first Switcher
1062 * page for this CPU is. This is an optimization: when the Switcher
1063 * saves the Guest registers, it saves them into the first page of this
1064 * CPU's "struct lguest_pages": if we make sure the Guest's register
1065 * page is already mapped there, we don't have to copy them out
1066 * again.
1067 */
1068 regs_pte = pfn_pte(__pa(cpu->regs_page) >> PAGE_SHIFT, PAGE_KERNEL);
1069 set_pte(&switcher_pte_page[pte_index((unsigned long)pages)], regs_pte);
1070}
1071/*:*/
1072
1073static void free_switcher_pte_pages(void)
1074{
1075 unsigned int i;
1076
1077 for_each_possible_cpu(i)
1078 free_page((long)switcher_pte_page(i));
1079}
1080
1081/*H:520
1082 * Setting up the Switcher PTE page for given CPU is fairly easy, given
1083 * the CPU number and the "struct page"s for the Switcher code itself.
1084 *
1085 * Currently the Switcher is less than a page long, so "pages" is always 1.
1086 */
1087static __init void populate_switcher_pte_page(unsigned int cpu,
1088 struct page *switcher_page[],
1089 unsigned int pages)
1090{
1091 unsigned int i;
1092 pte_t *pte = switcher_pte_page(cpu);
1093
1094 /* The first entries are easy: they map the Switcher code. */
1095 for (i = 0; i < pages; i++) {
1096 set_pte(&pte[i], mk_pte(switcher_page[i],
1097 __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
1098 }
1099
1100 /* The only other thing we map is this CPU's pair of pages. */
1101 i = pages + cpu*2;
1102
1103 /* First page (Guest registers) is writable from the Guest */
1104 set_pte(&pte[i], pfn_pte(page_to_pfn(switcher_page[i]),
1105 __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW)));
1106
1107 /*
1108 * The second page contains the "struct lguest_ro_state", and is
1109 * read-only.
1110 */
1111 set_pte(&pte[i+1], pfn_pte(page_to_pfn(switcher_page[i+1]),
1112 __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
1113}
1114
1115/*
1116 * We've made it through the page table code. Perhaps our tired brains are
1117 * still processing the details, or perhaps we're simply glad it's over.
1118 *
1119 * If nothing else, note that all this complexity in juggling shadow page tables
1120 * in sync with the Guest's page tables is for one reason: for most Guests this
1121 * page table dance determines how bad performance will be. This is why Xen
1122 * uses exotic direct Guest pagetable manipulation, and why both Intel and AMD
1123 * have implemented shadow page table support directly into hardware.
1124 *
1125 * There is just one file remaining in the Host.
1126 */
1127
1128/*H:510
1129 * At boot or module load time, init_pagetables() allocates and populates
1130 * the Switcher PTE page for each CPU.
1131 */
1132__init int init_pagetables(struct page **switcher_page, unsigned int pages)
1133{
1134 unsigned int i;
1135
1136 for_each_possible_cpu(i) {
1137 switcher_pte_page(i) = (pte_t *)get_zeroed_page(GFP_KERNEL);
1138 if (!switcher_pte_page(i)) {
1139 free_switcher_pte_pages();
1140 return -ENOMEM;
1141 }
1142 populate_switcher_pte_page(i, switcher_page, pages);
1143 }
1144 return 0;
1145}
1146/*:*/
1147
1148/* Cleaning up simply involves freeing the PTE page for each CPU. */
1149void free_pagetables(void)
1150{
1151 free_switcher_pte_pages();
1152}