576a8318221c9dfe47dc28a660565094c9ef7753
1 /*P:700 The pagetable code, on the other hand, still shows the scars of
2 * previous encounters. It's functional, and as neat as it can be in the
3 * circumstances, but be wary, for these things are subtle and break easily.
4 * The Guest provides a virtual to physical mapping, but we can neither trust
5 * it nor use it: we verify and convert it here then point the CPU to the
6 * converted Guest pages when running the Guest. :*/
8 /* Copyright (C) Rusty Russell IBM Corporation 2006.
9 * GPL v2 and any later version */
11 #include <linux/types.h>
12 #include <linux/spinlock.h>
13 #include <linux/random.h>
14 #include <linux/percpu.h>
15 #include <asm/tlbflush.h>
16 #include <asm/uaccess.h>
17 #include <asm/bootparam.h>
20 /*M:008 We hold reference to pages, which prevents them from being swapped.
21 * It'd be nice to have a callback in the "struct mm_struct" when Linux wants
22 * to swap out. If we had this, and a shrinker callback to trim PTE pages, we
23 * could probably consider launching Guests as non-root. :*/
28 * We use two-level page tables for the Guest. If you're not entirely
29 * comfortable with virtual addresses, physical addresses and page tables then
30 * I recommend you review arch/x86/lguest/boot.c's "Page Table Handling" (with
33 * The Guest keeps page tables, but we maintain the actual ones here: these are
34 * called "shadow" page tables. Which is a very Guest-centric name: these are
35 * the real page tables the CPU uses, although we keep them up to date to
36 * reflect the Guest's. (See what I mean about weird naming? Since when do
37 * shadows reflect anything?)
39 * Anyway, this is the most complicated part of the Host code. There are seven
41 * (i) Looking up a page table entry when the Guest faults,
42 * (ii) Making sure the Guest stack is mapped,
43 * (iii) Setting up a page table entry when the Guest tells us one has changed,
44 * (iv) Switching page tables,
45 * (v) Flushing (throwing away) page tables,
46 * (vi) Mapping the Switcher when the Guest is about to run,
47 * (vii) Setting up the page tables initially.
51 /* 1024 entries in a page table page maps 1024 pages: 4MB. The Switcher is
52 * conveniently placed at the top 4MB, so it uses a separate, complete PTE
54 #define SWITCHER_PGD_INDEX (PTRS_PER_PGD - 1)
56 /* We actually need a separate PTE page for each CPU. Remember that after the
57 * Switcher code itself comes two pages for each CPU, and we don't want this
58 * CPU's guest to see the pages of any other CPU. */
59 static DEFINE_PER_CPU(pte_t
*, switcher_pte_pages
);
60 #define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)
62 /*H:320 The page table code is curly enough to need helper functions to keep it
65 * There are two functions which return pointers to the shadow (aka "real")
68 * spgd_addr() takes the virtual address and returns a pointer to the top-level
69 * page directory entry (PGD) for that address. Since we keep track of several
70 * page tables, the "i" argument tells us which one we're interested in (it's
71 * usually the current one). */
72 static pgd_t
*spgd_addr(struct lg_cpu
*cpu
, u32 i
, unsigned long vaddr
)
74 unsigned int index
= pgd_index(vaddr
);
76 /* We kill any Guest trying to touch the Switcher addresses. */
77 if (index
>= SWITCHER_PGD_INDEX
) {
78 kill_guest(cpu
, "attempt to access switcher pages");
81 /* Return a pointer index'th pgd entry for the i'th page table. */
82 return &cpu
->lg
->pgdirs
[i
].pgdir
[index
];
85 /* This routine then takes the page directory entry returned above, which
86 * contains the address of the page table entry (PTE) page. It then returns a
87 * pointer to the PTE entry for the given address. */
88 static pte_t
*spte_addr(pgd_t spgd
, unsigned long vaddr
)
90 pte_t
*page
= __va(pgd_pfn(spgd
) << PAGE_SHIFT
);
91 /* You should never call this if the PGD entry wasn't valid */
92 BUG_ON(!(pgd_flags(spgd
) & _PAGE_PRESENT
));
93 return &page
[(vaddr
>> PAGE_SHIFT
) % PTRS_PER_PTE
];
96 /* These two functions just like the above two, except they access the Guest
97 * page tables. Hence they return a Guest address. */
98 static unsigned long gpgd_addr(struct lg_cpu
*cpu
, unsigned long vaddr
)
100 unsigned int index
= vaddr
>> (PGDIR_SHIFT
);
101 return cpu
->lg
->pgdirs
[cpu
->cpu_pgd
].gpgdir
+ index
* sizeof(pgd_t
);
104 static unsigned long gpte_addr(pgd_t gpgd
, unsigned long vaddr
)
106 unsigned long gpage
= pgd_pfn(gpgd
) << PAGE_SHIFT
;
107 BUG_ON(!(pgd_flags(gpgd
) & _PAGE_PRESENT
));
108 return gpage
+ ((vaddr
>>PAGE_SHIFT
) % PTRS_PER_PTE
) * sizeof(pte_t
);
112 /*M:014 get_pfn is slow: we could probably try to grab batches of pages here as
113 * an optimization (ie. pre-faulting). :*/
115 /*H:350 This routine takes a page number given by the Guest and converts it to
116 * an actual, physical page number. It can fail for several reasons: the
117 * virtual address might not be mapped by the Launcher, the write flag is set
118 * and the page is read-only, or the write flag was set and the page was
119 * shared so had to be copied, but we ran out of memory.
121 * This holds a reference to the page, so release_pte() is careful to put that
123 static unsigned long get_pfn(unsigned long virtpfn
, int write
)
127 /* gup me one page at this address please! */
128 if (get_user_pages_fast(virtpfn
<< PAGE_SHIFT
, 1, write
, &page
) == 1)
129 return page_to_pfn(page
);
131 /* This value indicates failure. */
135 /*H:340 Converting a Guest page table entry to a shadow (ie. real) page table
136 * entry can be a little tricky. The flags are (almost) the same, but the
137 * Guest PTE contains a virtual page number: the CPU needs the real page
139 static pte_t
gpte_to_spte(struct lg_cpu
*cpu
, pte_t gpte
, int write
)
141 unsigned long pfn
, base
, flags
;
143 /* The Guest sets the global flag, because it thinks that it is using
144 * PGE. We only told it to use PGE so it would tell us whether it was
145 * flushing a kernel mapping or a userspace mapping. We don't actually
146 * use the global bit, so throw it away. */
147 flags
= (pte_flags(gpte
) & ~_PAGE_GLOBAL
);
149 /* The Guest's pages are offset inside the Launcher. */
150 base
= (unsigned long)cpu
->lg
->mem_base
/ PAGE_SIZE
;
152 /* We need a temporary "unsigned long" variable to hold the answer from
153 * get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't
154 * fit in spte.pfn. get_pfn() finds the real physical number of the
155 * page, given the virtual number. */
156 pfn
= get_pfn(base
+ pte_pfn(gpte
), write
);
158 kill_guest(cpu
, "failed to get page %lu", pte_pfn(gpte
));
159 /* When we destroy the Guest, we'll go through the shadow page
160 * tables and release_pte() them. Make sure we don't think
161 * this one is valid! */
164 /* Now we assemble our shadow PTE from the page number and flags. */
165 return pfn_pte(pfn
, __pgprot(flags
));
168 /*H:460 And to complete the chain, release_pte() looks like this: */
169 static void release_pte(pte_t pte
)
171 /* Remember that get_user_pages_fast() took a reference to the page, in
172 * get_pfn()? We have to put it back now. */
173 if (pte_flags(pte
) & _PAGE_PRESENT
)
174 put_page(pfn_to_page(pte_pfn(pte
)));
178 static void check_gpte(struct lg_cpu
*cpu
, pte_t gpte
)
180 if ((pte_flags(gpte
) & _PAGE_PSE
) ||
181 pte_pfn(gpte
) >= cpu
->lg
->pfn_limit
)
182 kill_guest(cpu
, "bad page table entry");
185 static void check_gpgd(struct lg_cpu
*cpu
, pgd_t gpgd
)
187 if ((pgd_flags(gpgd
) & ~_PAGE_TABLE
) ||
188 (pgd_pfn(gpgd
) >= cpu
->lg
->pfn_limit
))
189 kill_guest(cpu
, "bad page directory entry");
193 * (i) Looking up a page table entry when the Guest faults.
195 * We saw this call in run_guest(): when we see a page fault in the Guest, we
196 * come here. That's because we only set up the shadow page tables lazily as
197 * they're needed, so we get page faults all the time and quietly fix them up
198 * and return to the Guest without it knowing.
200 * If we fixed up the fault (ie. we mapped the address), this routine returns
201 * true. Otherwise, it was a real fault and we need to tell the Guest. */
202 int demand_page(struct lg_cpu
*cpu
, unsigned long vaddr
, int errcode
)
206 unsigned long gpte_ptr
;
210 /* First step: get the top-level Guest page table entry. */
211 gpgd
= lgread(cpu
, gpgd_addr(cpu
, vaddr
), pgd_t
);
212 /* Toplevel not present? We can't map it in. */
213 if (!(pgd_flags(gpgd
) & _PAGE_PRESENT
))
216 /* Now look at the matching shadow entry. */
217 spgd
= spgd_addr(cpu
, cpu
->cpu_pgd
, vaddr
);
218 if (!(pgd_flags(*spgd
) & _PAGE_PRESENT
)) {
219 /* No shadow entry: allocate a new shadow PTE page. */
220 unsigned long ptepage
= get_zeroed_page(GFP_KERNEL
);
221 /* This is not really the Guest's fault, but killing it is
222 * simple for this corner case. */
224 kill_guest(cpu
, "out of memory allocating pte page");
227 /* We check that the Guest pgd is OK. */
228 check_gpgd(cpu
, gpgd
);
229 /* And we copy the flags to the shadow PGD entry. The page
230 * number in the shadow PGD is the page we just allocated. */
231 *spgd
= __pgd(__pa(ptepage
) | pgd_flags(gpgd
));
234 /* OK, now we look at the lower level in the Guest page table: keep its
235 * address, because we might update it later. */
236 gpte_ptr
= gpte_addr(gpgd
, vaddr
);
237 gpte
= lgread(cpu
, gpte_ptr
, pte_t
);
239 /* If this page isn't in the Guest page tables, we can't page it in. */
240 if (!(pte_flags(gpte
) & _PAGE_PRESENT
))
243 /* Check they're not trying to write to a page the Guest wants
244 * read-only (bit 2 of errcode == write). */
245 if ((errcode
& 2) && !(pte_flags(gpte
) & _PAGE_RW
))
248 /* User access to a kernel-only page? (bit 3 == user access) */
249 if ((errcode
& 4) && !(pte_flags(gpte
) & _PAGE_USER
))
252 /* Check that the Guest PTE flags are OK, and the page number is below
253 * the pfn_limit (ie. not mapping the Launcher binary). */
254 check_gpte(cpu
, gpte
);
256 /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
257 gpte
= pte_mkyoung(gpte
);
259 gpte
= pte_mkdirty(gpte
);
261 /* Get the pointer to the shadow PTE entry we're going to set. */
262 spte
= spte_addr(*spgd
, vaddr
);
263 /* If there was a valid shadow PTE entry here before, we release it.
264 * This can happen with a write to a previously read-only entry. */
267 /* If this is a write, we insist that the Guest page is writable (the
268 * final arg to gpte_to_spte()). */
270 *spte
= gpte_to_spte(cpu
, gpte
, 1);
272 /* If this is a read, don't set the "writable" bit in the page
273 * table entry, even if the Guest says it's writable. That way
274 * we will come back here when a write does actually occur, so
275 * we can update the Guest's _PAGE_DIRTY flag. */
276 *spte
= gpte_to_spte(cpu
, pte_wrprotect(gpte
), 0);
278 /* Finally, we write the Guest PTE entry back: we've set the
279 * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags. */
280 lgwrite(cpu
, gpte_ptr
, pte_t
, gpte
);
282 /* The fault is fixed, the page table is populated, the mapping
283 * manipulated, the result returned and the code complete. A small
284 * delay and a trace of alliteration are the only indications the Guest
285 * has that a page fault occurred at all. */
290 * (ii) Making sure the Guest stack is mapped.
292 * Remember that direct traps into the Guest need a mapped Guest kernel stack.
293 * pin_stack_pages() calls us here: we could simply call demand_page(), but as
294 * we've seen that logic is quite long, and usually the stack pages are already
295 * mapped, so it's overkill.
297 * This is a quick version which answers the question: is this virtual address
298 * mapped by the shadow page tables, and is it writable? */
299 static int page_writable(struct lg_cpu
*cpu
, unsigned long vaddr
)
304 /* Look at the current top level entry: is it present? */
305 spgd
= spgd_addr(cpu
, cpu
->cpu_pgd
, vaddr
);
306 if (!(pgd_flags(*spgd
) & _PAGE_PRESENT
))
309 /* Check the flags on the pte entry itself: it must be present and
311 flags
= pte_flags(*(spte_addr(*spgd
, vaddr
)));
313 return (flags
& (_PAGE_PRESENT
|_PAGE_RW
)) == (_PAGE_PRESENT
|_PAGE_RW
);
316 /* So, when pin_stack_pages() asks us to pin a page, we check if it's already
317 * in the page tables, and if not, we call demand_page() with error code 2
318 * (meaning "write"). */
319 void pin_page(struct lg_cpu
*cpu
, unsigned long vaddr
)
321 if (!page_writable(cpu
, vaddr
) && !demand_page(cpu
, vaddr
, 2))
322 kill_guest(cpu
, "bad stack page %#lx", vaddr
);
325 /*H:450 If we chase down the release_pgd() code, it looks like this: */
326 static void release_pgd(struct lguest
*lg
, pgd_t
*spgd
)
328 /* If the entry's not present, there's nothing to release. */
329 if (pgd_flags(*spgd
) & _PAGE_PRESENT
) {
331 /* Converting the pfn to find the actual PTE page is easy: turn
332 * the page number into a physical address, then convert to a
333 * virtual address (easy for kernel pages like this one). */
334 pte_t
*ptepage
= __va(pgd_pfn(*spgd
) << PAGE_SHIFT
);
335 /* For each entry in the page, we might need to release it. */
336 for (i
= 0; i
< PTRS_PER_PTE
; i
++)
337 release_pte(ptepage
[i
]);
338 /* Now we can free the page of PTEs */
339 free_page((long)ptepage
);
340 /* And zero out the PGD entry so we never release it twice. */
345 /*H:445 We saw flush_user_mappings() twice: once from the flush_user_mappings()
346 * hypercall and once in new_pgdir() when we re-used a top-level pgdir page.
347 * It simply releases every PTE page from 0 up to the Guest's kernel address. */
348 static void flush_user_mappings(struct lguest
*lg
, int idx
)
351 /* Release every pgd entry up to the kernel's address. */
352 for (i
= 0; i
< pgd_index(lg
->kernel_address
); i
++)
353 release_pgd(lg
, lg
->pgdirs
[idx
].pgdir
+ i
);
356 /*H:440 (v) Flushing (throwing away) page tables,
358 * The Guest has a hypercall to throw away the page tables: it's used when a
359 * large number of mappings have been changed. */
360 void guest_pagetable_flush_user(struct lg_cpu
*cpu
)
362 /* Drop the userspace part of the current page table. */
363 flush_user_mappings(cpu
->lg
, cpu
->cpu_pgd
);
367 /* We walk down the guest page tables to get a guest-physical address */
368 unsigned long guest_pa(struct lg_cpu
*cpu
, unsigned long vaddr
)
373 /* First step: get the top-level Guest page table entry. */
374 gpgd
= lgread(cpu
, gpgd_addr(cpu
, vaddr
), pgd_t
);
375 /* Toplevel not present? We can't map it in. */
376 if (!(pgd_flags(gpgd
) & _PAGE_PRESENT
))
377 kill_guest(cpu
, "Bad address %#lx", vaddr
);
379 gpte
= lgread(cpu
, gpte_addr(gpgd
, vaddr
), pte_t
);
380 if (!(pte_flags(gpte
) & _PAGE_PRESENT
))
381 kill_guest(cpu
, "Bad address %#lx", vaddr
);
383 return pte_pfn(gpte
) * PAGE_SIZE
| (vaddr
& ~PAGE_MASK
);
386 /* We keep several page tables. This is a simple routine to find the page
387 * table (if any) corresponding to this top-level address the Guest has given
389 static unsigned int find_pgdir(struct lguest
*lg
, unsigned long pgtable
)
392 for (i
= 0; i
< ARRAY_SIZE(lg
->pgdirs
); i
++)
393 if (lg
->pgdirs
[i
].pgdir
&& lg
->pgdirs
[i
].gpgdir
== pgtable
)
398 /*H:435 And this is us, creating the new page directory. If we really do
399 * allocate a new one (and so the kernel parts are not there), we set
401 static unsigned int new_pgdir(struct lg_cpu
*cpu
,
402 unsigned long gpgdir
,
407 /* We pick one entry at random to throw out. Choosing the Least
408 * Recently Used might be better, but this is easy. */
409 next
= random32() % ARRAY_SIZE(cpu
->lg
->pgdirs
);
410 /* If it's never been allocated at all before, try now. */
411 if (!cpu
->lg
->pgdirs
[next
].pgdir
) {
412 cpu
->lg
->pgdirs
[next
].pgdir
=
413 (pgd_t
*)get_zeroed_page(GFP_KERNEL
);
414 /* If the allocation fails, just keep using the one we have */
415 if (!cpu
->lg
->pgdirs
[next
].pgdir
)
418 /* This is a blank page, so there are no kernel
419 * mappings: caller must map the stack! */
422 /* Record which Guest toplevel this shadows. */
423 cpu
->lg
->pgdirs
[next
].gpgdir
= gpgdir
;
424 /* Release all the non-kernel mappings. */
425 flush_user_mappings(cpu
->lg
, next
);
430 /*H:430 (iv) Switching page tables
432 * Now we've seen all the page table setting and manipulation, let's see what
433 * what happens when the Guest changes page tables (ie. changes the top-level
434 * pgdir). This occurs on almost every context switch. */
435 void guest_new_pagetable(struct lg_cpu
*cpu
, unsigned long pgtable
)
437 int newpgdir
, repin
= 0;
439 /* Look to see if we have this one already. */
440 newpgdir
= find_pgdir(cpu
->lg
, pgtable
);
441 /* If not, we allocate or mug an existing one: if it's a fresh one,
442 * repin gets set to 1. */
443 if (newpgdir
== ARRAY_SIZE(cpu
->lg
->pgdirs
))
444 newpgdir
= new_pgdir(cpu
, pgtable
, &repin
);
445 /* Change the current pgd index to the new one. */
446 cpu
->cpu_pgd
= newpgdir
;
447 /* If it was completely blank, we map in the Guest kernel stack */
449 pin_stack_pages(cpu
);
452 /*H:470 Finally, a routine which throws away everything: all PGD entries in all
453 * the shadow page tables, including the Guest's kernel mappings. This is used
454 * when we destroy the Guest. */
455 static void release_all_pagetables(struct lguest
*lg
)
459 /* Every shadow pagetable this Guest has */
460 for (i
= 0; i
< ARRAY_SIZE(lg
->pgdirs
); i
++)
461 if (lg
->pgdirs
[i
].pgdir
)
462 /* Every PGD entry except the Switcher at the top */
463 for (j
= 0; j
< SWITCHER_PGD_INDEX
; j
++)
464 release_pgd(lg
, lg
->pgdirs
[i
].pgdir
+ j
);
467 /* We also throw away everything when a Guest tells us it's changed a kernel
468 * mapping. Since kernel mappings are in every page table, it's easiest to
469 * throw them all away. This traps the Guest in amber for a while as
470 * everything faults back in, but it's rare. */
471 void guest_pagetable_clear_all(struct lg_cpu
*cpu
)
473 release_all_pagetables(cpu
->lg
);
474 /* We need the Guest kernel stack mapped again. */
475 pin_stack_pages(cpu
);
478 /*M:009 Since we throw away all mappings when a kernel mapping changes, our
479 * performance sucks for guests using highmem. In fact, a guest with
480 * PAGE_OFFSET 0xc0000000 (the default) and more than about 700MB of RAM is
481 * usually slower than a Guest with less memory.
483 * This, of course, cannot be fixed. It would take some kind of... well, I
484 * don't know, but the term "puissant code-fu" comes to mind. :*/
486 /*H:420 This is the routine which actually sets the page table entry for then
487 * "idx"'th shadow page table.
489 * Normally, we can just throw out the old entry and replace it with 0: if they
490 * use it demand_page() will put the new entry in. We need to do this anyway:
491 * The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page
492 * is read from, and _PAGE_DIRTY when it's written to.
494 * But Avi Kivity pointed out that most Operating Systems (Linux included) set
495 * these bits on PTEs immediately anyway. This is done to save the CPU from
496 * having to update them, but it helps us the same way: if they set
497 * _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if
498 * they set _PAGE_DIRTY then we can put a writable PTE entry in immediately.
500 static void do_set_pte(struct lg_cpu
*cpu
, int idx
,
501 unsigned long vaddr
, pte_t gpte
)
503 /* Look up the matching shadow page directory entry. */
504 pgd_t
*spgd
= spgd_addr(cpu
, idx
, vaddr
);
506 /* If the top level isn't present, there's no entry to update. */
507 if (pgd_flags(*spgd
) & _PAGE_PRESENT
) {
508 /* Otherwise, we start by releasing the existing entry. */
509 pte_t
*spte
= spte_addr(*spgd
, vaddr
);
512 /* If they're setting this entry as dirty or accessed, we might
513 * as well put that entry they've given us in now. This shaves
514 * 10% off a copy-on-write micro-benchmark. */
515 if (pte_flags(gpte
) & (_PAGE_DIRTY
| _PAGE_ACCESSED
)) {
516 check_gpte(cpu
, gpte
);
517 *spte
= gpte_to_spte(cpu
, gpte
,
518 pte_flags(gpte
) & _PAGE_DIRTY
);
520 /* Otherwise kill it and we can demand_page() it in
526 /*H:410 Updating a PTE entry is a little trickier.
528 * We keep track of several different page tables (the Guest uses one for each
529 * process, so it makes sense to cache at least a few). Each of these have
530 * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for
531 * all processes. So when the page table above that address changes, we update
532 * all the page tables, not just the current one. This is rare.
534 * The benefit is that when we have to track a new page table, we can keep all
535 * the kernel mappings. This speeds up context switch immensely. */
536 void guest_set_pte(struct lg_cpu
*cpu
,
537 unsigned long gpgdir
, unsigned long vaddr
, pte_t gpte
)
539 /* Kernel mappings must be changed on all top levels. Slow, but doesn't
541 if (vaddr
>= cpu
->lg
->kernel_address
) {
543 for (i
= 0; i
< ARRAY_SIZE(cpu
->lg
->pgdirs
); i
++)
544 if (cpu
->lg
->pgdirs
[i
].pgdir
)
545 do_set_pte(cpu
, i
, vaddr
, gpte
);
547 /* Is this page table one we have a shadow for? */
548 int pgdir
= find_pgdir(cpu
->lg
, gpgdir
);
549 if (pgdir
!= ARRAY_SIZE(cpu
->lg
->pgdirs
))
550 /* If so, do the update. */
551 do_set_pte(cpu
, pgdir
, vaddr
, gpte
);
556 * (iii) Setting up a page table entry when the Guest tells us one has changed.
558 * Just like we did in interrupts_and_traps.c, it makes sense for us to deal
559 * with the other side of page tables while we're here: what happens when the
560 * Guest asks for a page table to be updated?
562 * We already saw that demand_page() will fill in the shadow page tables when
563 * needed, so we can simply remove shadow page table entries whenever the Guest
564 * tells us they've changed. When the Guest tries to use the new entry it will
565 * fault and demand_page() will fix it up.
567 * So with that in mind here's our code to to update a (top-level) PGD entry:
569 void guest_set_pmd(struct lguest
*lg
, unsigned long gpgdir
, u32 idx
)
573 /* The kernel seems to try to initialize this early on: we ignore its
574 * attempts to map over the Switcher. */
575 if (idx
>= SWITCHER_PGD_INDEX
)
578 /* If they're talking about a page table we have a shadow for... */
579 pgdir
= find_pgdir(lg
, gpgdir
);
580 if (pgdir
< ARRAY_SIZE(lg
->pgdirs
))
581 /* ... throw it away. */
582 release_pgd(lg
, lg
->pgdirs
[pgdir
].pgdir
+ idx
);
585 /* Once we know how much memory we have we can construct simple identity
586 * (which set virtual == physical) and linear mappings
587 * which will get the Guest far enough into the boot to create its own.
589 * We lay them out of the way, just below the initrd (which is why we need to
590 * know its size here). */
591 static unsigned long setup_pagetables(struct lguest
*lg
,
593 unsigned long initrd_size
)
596 pte_t __user
*linear
;
597 unsigned int mapped_pages
, i
, linear_pages
, phys_linear
;
598 unsigned long mem_base
= (unsigned long)lg
->mem_base
;
600 /* We have mapped_pages frames to map, so we need
601 * linear_pages page tables to map them. */
602 mapped_pages
= mem
/ PAGE_SIZE
;
603 linear_pages
= (mapped_pages
+ PTRS_PER_PTE
- 1) / PTRS_PER_PTE
;
605 /* We put the toplevel page directory page at the top of memory. */
606 pgdir
= (pgd_t
*)(mem
+ mem_base
- initrd_size
- PAGE_SIZE
);
608 /* Now we use the next linear_pages pages as pte pages */
609 linear
= (void *)pgdir
- linear_pages
* PAGE_SIZE
;
611 /* Linear mapping is easy: put every page's address into the
612 * mapping in order. */
613 for (i
= 0; i
< mapped_pages
; i
++) {
615 pte
= pfn_pte(i
, __pgprot(_PAGE_PRESENT
|_PAGE_RW
|_PAGE_USER
));
616 if (copy_to_user(&linear
[i
], &pte
, sizeof(pte
)) != 0)
620 /* The top level points to the linear page table pages above.
621 * We setup the identity and linear mappings here. */
622 phys_linear
= (unsigned long)linear
- mem_base
;
623 for (i
= 0; i
< mapped_pages
; i
+= PTRS_PER_PTE
) {
625 pgd
= __pgd((phys_linear
+ i
* sizeof(pte_t
)) |
626 (_PAGE_PRESENT
| _PAGE_RW
| _PAGE_USER
));
628 if (copy_to_user(&pgdir
[i
/ PTRS_PER_PTE
], &pgd
, sizeof(pgd
))
629 || copy_to_user(&pgdir
[pgd_index(PAGE_OFFSET
)
635 /* We return the top level (guest-physical) address: remember where
637 return (unsigned long)pgdir
- mem_base
;
640 /*H:500 (vii) Setting up the page tables initially.
642 * When a Guest is first created, the Launcher tells us where the toplevel of
643 * its first page table is. We set some things up here: */
644 int init_guest_pagetable(struct lguest
*lg
)
648 struct boot_params __user
*boot
= (struct boot_params
*)lg
->mem_base
;
650 /* Get the Guest memory size and the ramdisk size from the boot header
651 * located at lg->mem_base (Guest address 0). */
652 if (copy_from_user(&mem
, &boot
->e820_map
[0].size
, sizeof(mem
))
653 || get_user(initrd_size
, &boot
->hdr
.ramdisk_size
))
656 /* We start on the first shadow page table, and give it a blank PGD
658 lg
->pgdirs
[0].gpgdir
= setup_pagetables(lg
, mem
, initrd_size
);
659 if (IS_ERR_VALUE(lg
->pgdirs
[0].gpgdir
))
660 return lg
->pgdirs
[0].gpgdir
;
661 lg
->pgdirs
[0].pgdir
= (pgd_t
*)get_zeroed_page(GFP_KERNEL
);
662 if (!lg
->pgdirs
[0].pgdir
)
664 lg
->cpus
[0].cpu_pgd
= 0;
668 /* When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
669 void page_table_guest_data_init(struct lg_cpu
*cpu
)
671 /* We get the kernel address: above this is all kernel memory. */
672 if (get_user(cpu
->lg
->kernel_address
,
673 &cpu
->lg
->lguest_data
->kernel_address
)
674 /* We tell the Guest that it can't use the top 4MB of virtual
675 * addresses used by the Switcher. */
676 || put_user(4U*1024*1024, &cpu
->lg
->lguest_data
->reserve_mem
)
677 || put_user(cpu
->lg
->pgdirs
[0].gpgdir
, &cpu
->lg
->lguest_data
->pgdir
))
678 kill_guest(cpu
, "bad guest page %p", cpu
->lg
->lguest_data
);
680 /* In flush_user_mappings() we loop from 0 to
681 * "pgd_index(lg->kernel_address)". This assumes it won't hit the
682 * Switcher mappings, so check that now. */
683 if (pgd_index(cpu
->lg
->kernel_address
) >= SWITCHER_PGD_INDEX
)
684 kill_guest(cpu
, "bad kernel address %#lx",
685 cpu
->lg
->kernel_address
);
688 /* When a Guest dies, our cleanup is fairly simple. */
689 void free_guest_pagetable(struct lguest
*lg
)
693 /* Throw away all page table pages. */
694 release_all_pagetables(lg
);
695 /* Now free the top levels: free_page() can handle 0 just fine. */
696 for (i
= 0; i
< ARRAY_SIZE(lg
->pgdirs
); i
++)
697 free_page((long)lg
->pgdirs
[i
].pgdir
);
700 /*H:480 (vi) Mapping the Switcher when the Guest is about to run.
702 * The Switcher and the two pages for this CPU need to be visible in the
703 * Guest (and not the pages for other CPUs). We have the appropriate PTE pages
704 * for each CPU already set up, we just need to hook them in now we know which
705 * Guest is about to run on this CPU. */
706 void map_switcher_in_guest(struct lg_cpu
*cpu
, struct lguest_pages
*pages
)
708 pte_t
*switcher_pte_page
= __get_cpu_var(switcher_pte_pages
);
713 /* Make the last PGD entry for this Guest point to the Switcher's PTE
714 * page for this CPU (with appropriate flags). */
715 switcher_pgd
= __pgd(__pa(switcher_pte_page
) | __PAGE_KERNEL
);
717 cpu
->lg
->pgdirs
[cpu
->cpu_pgd
].pgdir
[SWITCHER_PGD_INDEX
] = switcher_pgd
;
719 /* We also change the Switcher PTE page. When we're running the Guest,
720 * we want the Guest's "regs" page to appear where the first Switcher
721 * page for this CPU is. This is an optimization: when the Switcher
722 * saves the Guest registers, it saves them into the first page of this
723 * CPU's "struct lguest_pages": if we make sure the Guest's register
724 * page is already mapped there, we don't have to copy them out
726 pfn
= __pa(cpu
->regs_page
) >> PAGE_SHIFT
;
727 regs_pte
= pfn_pte(pfn
, __pgprot(__PAGE_KERNEL
));
728 switcher_pte_page
[(unsigned long)pages
/PAGE_SIZE
%PTRS_PER_PTE
] = regs_pte
;
732 static void free_switcher_pte_pages(void)
736 for_each_possible_cpu(i
)
737 free_page((long)switcher_pte_page(i
));
740 /*H:520 Setting up the Switcher PTE page for given CPU is fairly easy, given
741 * the CPU number and the "struct page"s for the Switcher code itself.
743 * Currently the Switcher is less than a page long, so "pages" is always 1. */
744 static __init
void populate_switcher_pte_page(unsigned int cpu
,
745 struct page
*switcher_page
[],
749 pte_t
*pte
= switcher_pte_page(cpu
);
751 /* The first entries are easy: they map the Switcher code. */
752 for (i
= 0; i
< pages
; i
++) {
753 pte
[i
] = mk_pte(switcher_page
[i
],
754 __pgprot(_PAGE_PRESENT
|_PAGE_ACCESSED
));
757 /* The only other thing we map is this CPU's pair of pages. */
760 /* First page (Guest registers) is writable from the Guest */
761 pte
[i
] = pfn_pte(page_to_pfn(switcher_page
[i
]),
762 __pgprot(_PAGE_PRESENT
|_PAGE_ACCESSED
|_PAGE_RW
));
764 /* The second page contains the "struct lguest_ro_state", and is
766 pte
[i
+1] = pfn_pte(page_to_pfn(switcher_page
[i
+1]),
767 __pgprot(_PAGE_PRESENT
|_PAGE_ACCESSED
));
770 /* We've made it through the page table code. Perhaps our tired brains are
771 * still processing the details, or perhaps we're simply glad it's over.
773 * If nothing else, note that all this complexity in juggling shadow page tables
774 * in sync with the Guest's page tables is for one reason: for most Guests this
775 * page table dance determines how bad performance will be. This is why Xen
776 * uses exotic direct Guest pagetable manipulation, and why both Intel and AMD
777 * have implemented shadow page table support directly into hardware.
779 * There is just one file remaining in the Host. */
781 /*H:510 At boot or module load time, init_pagetables() allocates and populates
782 * the Switcher PTE page for each CPU. */
783 __init
int init_pagetables(struct page
**switcher_page
, unsigned int pages
)
787 for_each_possible_cpu(i
) {
788 switcher_pte_page(i
) = (pte_t
*)get_zeroed_page(GFP_KERNEL
);
789 if (!switcher_pte_page(i
)) {
790 free_switcher_pte_pages();
793 populate_switcher_pte_page(i
, switcher_page
, pages
);
799 /* Cleaning up simply involves freeing the PTE page for each CPU. */
800 void free_pagetables(void)
802 free_switcher_pte_pages();
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