4 * This file contains the various mmu fetch and update operations.
5 * The most important job they must perform is the mapping between the
6 * domain's pfn and the overall machine mfns.
8 * Xen allows guests to directly update the pagetable, in a controlled
9 * fashion. In other words, the guest modifies the same pagetable
10 * that the CPU actually uses, which eliminates the overhead of having
11 * a separate shadow pagetable.
13 * In order to allow this, it falls on the guest domain to map its
14 * notion of a "physical" pfn - which is just a domain-local linear
15 * address - into a real "machine address" which the CPU's MMU can
18 * A pgd_t/pmd_t/pte_t will typically contain an mfn, and so can be
19 * inserted directly into the pagetable. When creating a new
20 * pte/pmd/pgd, it converts the passed pfn into an mfn. Conversely,
21 * when reading the content back with __(pgd|pmd|pte)_val, it converts
22 * the mfn back into a pfn.
24 * The other constraint is that all pages which make up a pagetable
25 * must be mapped read-only in the guest. This prevents uncontrolled
26 * guest updates to the pagetable. Xen strictly enforces this, and
27 * will disallow any pagetable update which will end up mapping a
28 * pagetable page RW, and will disallow using any writable page as a
31 * Naively, when loading %cr3 with the base of a new pagetable, Xen
32 * would need to validate the whole pagetable before going on.
33 * Naturally, this is quite slow. The solution is to "pin" a
34 * pagetable, which enforces all the constraints on the pagetable even
35 * when it is not actively in use. This menas that Xen can be assured
36 * that it is still valid when you do load it into %cr3, and doesn't
37 * need to revalidate it.
39 * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
41 #include <linux/sched.h>
42 #include <linux/highmem.h>
43 #include <linux/bug.h>
45 #include <asm/pgtable.h>
46 #include <asm/tlbflush.h>
47 #include <asm/mmu_context.h>
48 #include <asm/paravirt.h>
50 #include <asm/xen/hypercall.h>
51 #include <asm/xen/hypervisor.h>
54 #include <xen/interface/xen.h>
56 #include "multicalls.h"
59 #define P2M_ENTRIES_PER_PAGE (PAGE_SIZE / sizeof(unsigned long))
60 #define TOP_ENTRIES (MAX_DOMAIN_PAGES / P2M_ENTRIES_PER_PAGE)
62 /* Placeholder for holes in the address space */
63 static unsigned long p2m_missing[P2M_ENTRIES_PER_PAGE]
64 __attribute__((section(".data.page_aligned"))) =
65 { [ 0 ... P2M_ENTRIES_PER_PAGE-1 ] = ~0UL };
67 /* Array of pointers to pages containing p2m entries */
68 static unsigned long *p2m_top[TOP_ENTRIES]
69 __attribute__((section(".data.page_aligned"))) =
70 { [ 0 ... TOP_ENTRIES - 1] = &p2m_missing[0] };
72 /* Arrays of p2m arrays expressed in mfns used for save/restore */
73 static unsigned long p2m_top_mfn[TOP_ENTRIES]
74 __attribute__((section(".bss.page_aligned")));
76 static unsigned long p2m_top_mfn_list[
77 PAGE_ALIGN(TOP_ENTRIES / P2M_ENTRIES_PER_PAGE)]
78 __attribute__((section(".bss.page_aligned")));
80 static inline unsigned p2m_top_index(unsigned long pfn)
82 BUG_ON(pfn >= MAX_DOMAIN_PAGES);
83 return pfn / P2M_ENTRIES_PER_PAGE;
86 static inline unsigned p2m_index(unsigned long pfn)
88 return pfn % P2M_ENTRIES_PER_PAGE;
91 /* Build the parallel p2m_top_mfn structures */
92 void xen_setup_mfn_list_list(void)
96 for(pfn = 0; pfn < MAX_DOMAIN_PAGES; pfn += P2M_ENTRIES_PER_PAGE) {
97 unsigned topidx = p2m_top_index(pfn);
99 p2m_top_mfn[topidx] = virt_to_mfn(p2m_top[topidx]);
102 for(idx = 0; idx < ARRAY_SIZE(p2m_top_mfn_list); idx++) {
103 unsigned topidx = idx * P2M_ENTRIES_PER_PAGE;
104 p2m_top_mfn_list[idx] = virt_to_mfn(&p2m_top_mfn[topidx]);
107 BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);
109 HYPERVISOR_shared_info->arch.pfn_to_mfn_frame_list_list =
110 virt_to_mfn(p2m_top_mfn_list);
111 HYPERVISOR_shared_info->arch.max_pfn = xen_start_info->nr_pages;
114 /* Set up p2m_top to point to the domain-builder provided p2m pages */
115 void __init xen_build_dynamic_phys_to_machine(void)
117 unsigned long *mfn_list = (unsigned long *)xen_start_info->mfn_list;
118 unsigned long max_pfn = min(MAX_DOMAIN_PAGES, xen_start_info->nr_pages);
121 for(pfn = 0; pfn < max_pfn; pfn += P2M_ENTRIES_PER_PAGE) {
122 unsigned topidx = p2m_top_index(pfn);
124 p2m_top[topidx] = &mfn_list[pfn];
128 unsigned long get_phys_to_machine(unsigned long pfn)
130 unsigned topidx, idx;
132 if (unlikely(pfn >= MAX_DOMAIN_PAGES))
133 return INVALID_P2M_ENTRY;
135 topidx = p2m_top_index(pfn);
136 idx = p2m_index(pfn);
137 return p2m_top[topidx][idx];
139 EXPORT_SYMBOL_GPL(get_phys_to_machine);
141 static void alloc_p2m(unsigned long **pp, unsigned long *mfnp)
146 p = (void *)__get_free_page(GFP_KERNEL | __GFP_NOFAIL);
149 for(i = 0; i < P2M_ENTRIES_PER_PAGE; i++)
150 p[i] = INVALID_P2M_ENTRY;
152 if (cmpxchg(pp, p2m_missing, p) != p2m_missing)
153 free_page((unsigned long)p);
155 *mfnp = virt_to_mfn(p);
158 void set_phys_to_machine(unsigned long pfn, unsigned long mfn)
160 unsigned topidx, idx;
162 if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
163 BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
167 if (unlikely(pfn >= MAX_DOMAIN_PAGES)) {
168 BUG_ON(mfn != INVALID_P2M_ENTRY);
172 topidx = p2m_top_index(pfn);
173 if (p2m_top[topidx] == p2m_missing) {
174 /* no need to allocate a page to store an invalid entry */
175 if (mfn == INVALID_P2M_ENTRY)
177 alloc_p2m(&p2m_top[topidx], &p2m_top_mfn[topidx]);
180 idx = p2m_index(pfn);
181 p2m_top[topidx][idx] = mfn;
184 xmaddr_t arbitrary_virt_to_machine(unsigned long address)
187 pte_t *pte = lookup_address(address, &level);
188 unsigned offset = address & ~PAGE_MASK;
192 return XMADDR((pte_mfn(*pte) << PAGE_SHIFT) + offset);
195 void make_lowmem_page_readonly(void *vaddr)
198 unsigned long address = (unsigned long)vaddr;
201 pte = lookup_address(address, &level);
204 ptev = pte_wrprotect(*pte);
206 if (HYPERVISOR_update_va_mapping(address, ptev, 0))
210 void make_lowmem_page_readwrite(void *vaddr)
213 unsigned long address = (unsigned long)vaddr;
216 pte = lookup_address(address, &level);
219 ptev = pte_mkwrite(*pte);
221 if (HYPERVISOR_update_va_mapping(address, ptev, 0))
226 static bool page_pinned(void *ptr)
228 struct page *page = virt_to_page(ptr);
230 return PagePinned(page);
233 void xen_set_pmd_hyper(pmd_t *ptr, pmd_t val)
235 struct multicall_space mcs;
236 struct mmu_update *u;
240 mcs = xen_mc_entry(sizeof(*u));
242 u->ptr = virt_to_machine(ptr).maddr;
243 u->val = pmd_val_ma(val);
244 MULTI_mmu_update(mcs.mc, u, 1, NULL, DOMID_SELF);
246 xen_mc_issue(PARAVIRT_LAZY_MMU);
251 void xen_set_pmd(pmd_t *ptr, pmd_t val)
253 /* If page is not pinned, we can just update the entry
255 if (!page_pinned(ptr)) {
260 xen_set_pmd_hyper(ptr, val);
264 * Associate a virtual page frame with a given physical page frame
265 * and protection flags for that frame.
267 void set_pte_mfn(unsigned long vaddr, unsigned long mfn, pgprot_t flags)
274 pgd = swapper_pg_dir + pgd_index(vaddr);
275 if (pgd_none(*pgd)) {
279 pud = pud_offset(pgd, vaddr);
280 if (pud_none(*pud)) {
284 pmd = pmd_offset(pud, vaddr);
285 if (pmd_none(*pmd)) {
289 pte = pte_offset_kernel(pmd, vaddr);
290 /* <mfn,flags> stored as-is, to permit clearing entries */
291 xen_set_pte(pte, mfn_pte(mfn, flags));
294 * It's enough to flush this one mapping.
295 * (PGE mappings get flushed as well)
297 __flush_tlb_one(vaddr);
300 void xen_set_pte_at(struct mm_struct *mm, unsigned long addr,
301 pte_t *ptep, pte_t pteval)
303 /* updates to init_mm may be done without lock */
307 if (mm == current->mm || mm == &init_mm) {
308 if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
309 struct multicall_space mcs;
310 mcs = xen_mc_entry(0);
312 MULTI_update_va_mapping(mcs.mc, addr, pteval, 0);
313 xen_mc_issue(PARAVIRT_LAZY_MMU);
316 if (HYPERVISOR_update_va_mapping(addr, pteval, 0) == 0)
319 xen_set_pte(ptep, pteval);
326 /* Assume pteval_t is equivalent to all the other *val_t types. */
327 static pteval_t pte_mfn_to_pfn(pteval_t val)
329 if (val & _PAGE_PRESENT) {
330 unsigned long mfn = (val & PTE_MASK) >> PAGE_SHIFT;
331 pteval_t flags = val & ~PTE_MASK;
332 val = (mfn_to_pfn(mfn) << PAGE_SHIFT) | flags;
338 static pteval_t pte_pfn_to_mfn(pteval_t val)
340 if (val & _PAGE_PRESENT) {
341 unsigned long pfn = (val & PTE_MASK) >> PAGE_SHIFT;
342 pteval_t flags = val & ~PTE_MASK;
343 val = (pfn_to_mfn(pfn) << PAGE_SHIFT) | flags;
349 pteval_t xen_pte_val(pte_t pte)
351 return pte_mfn_to_pfn(pte.pte);
354 pgdval_t xen_pgd_val(pgd_t pgd)
356 return pte_mfn_to_pfn(pgd.pgd);
359 pte_t xen_make_pte(pteval_t pte)
361 pte = pte_pfn_to_mfn(pte);
362 return native_make_pte(pte);
365 pgd_t xen_make_pgd(pgdval_t pgd)
367 pgd = pte_pfn_to_mfn(pgd);
368 return native_make_pgd(pgd);
371 pmdval_t xen_pmd_val(pmd_t pmd)
373 return pte_mfn_to_pfn(pmd.pmd);
376 void xen_set_pud_hyper(pud_t *ptr, pud_t val)
378 struct multicall_space mcs;
379 struct mmu_update *u;
383 mcs = xen_mc_entry(sizeof(*u));
385 u->ptr = virt_to_machine(ptr).maddr;
386 u->val = pud_val_ma(val);
387 MULTI_mmu_update(mcs.mc, u, 1, NULL, DOMID_SELF);
389 xen_mc_issue(PARAVIRT_LAZY_MMU);
394 void xen_set_pud(pud_t *ptr, pud_t val)
396 /* If page is not pinned, we can just update the entry
398 if (!page_pinned(ptr)) {
403 xen_set_pud_hyper(ptr, val);
406 void xen_set_pte(pte_t *ptep, pte_t pte)
408 ptep->pte_high = pte.pte_high;
410 ptep->pte_low = pte.pte_low;
413 void xen_set_pte_atomic(pte_t *ptep, pte_t pte)
415 set_64bit((u64 *)ptep, pte_val_ma(pte));
418 void xen_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
421 smp_wmb(); /* make sure low gets written first */
425 void xen_pmd_clear(pmd_t *pmdp)
427 set_pmd(pmdp, __pmd(0));
430 pmd_t xen_make_pmd(pmdval_t pmd)
432 pmd = pte_pfn_to_mfn(pmd);
433 return native_make_pmd(pmd);
437 (Yet another) pagetable walker. This one is intended for pinning a
438 pagetable. This means that it walks a pagetable and calls the
439 callback function on each page it finds making up the page table,
440 at every level. It walks the entire pagetable, but it only bothers
441 pinning pte pages which are below pte_limit. In the normal case
442 this will be TASK_SIZE, but at boot we need to pin up to
443 FIXADDR_TOP. But the important bit is that we don't pin beyond
444 there, because then we start getting into Xen's ptes.
446 static int pgd_walk(pgd_t *pgd_base, int (*func)(struct page *, enum pt_level),
449 pgd_t *pgd = pgd_base;
451 unsigned long addr = 0;
452 unsigned long pgd_next;
454 BUG_ON(limit > FIXADDR_TOP);
456 if (xen_feature(XENFEAT_auto_translated_physmap))
459 for (; addr != FIXADDR_TOP; pgd++, addr = pgd_next) {
461 unsigned long pud_limit, pud_next;
463 pgd_next = pud_limit = pgd_addr_end(addr, FIXADDR_TOP);
468 pud = pud_offset(pgd, 0);
470 if (PTRS_PER_PUD > 1) /* not folded */
471 flush |= (*func)(virt_to_page(pud), PT_PUD);
473 for (; addr != pud_limit; pud++, addr = pud_next) {
475 unsigned long pmd_limit;
477 pud_next = pud_addr_end(addr, pud_limit);
479 if (pud_next < limit)
480 pmd_limit = pud_next;
487 pmd = pmd_offset(pud, 0);
489 if (PTRS_PER_PMD > 1) /* not folded */
490 flush |= (*func)(virt_to_page(pmd), PT_PMD);
492 for (; addr != pmd_limit; pmd++) {
493 addr += (PAGE_SIZE * PTRS_PER_PTE);
494 if ((pmd_limit-1) < (addr-1)) {
502 flush |= (*func)(pmd_page(*pmd), PT_PTE);
507 flush |= (*func)(virt_to_page(pgd_base), PT_PGD);
512 static spinlock_t *lock_pte(struct page *page)
514 spinlock_t *ptl = NULL;
516 #if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
517 ptl = __pte_lockptr(page);
524 static void do_unlock(void *v)
530 static void xen_do_pin(unsigned level, unsigned long pfn)
532 struct mmuext_op *op;
533 struct multicall_space mcs;
535 mcs = __xen_mc_entry(sizeof(*op));
538 op->arg1.mfn = pfn_to_mfn(pfn);
539 MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
542 static int pin_page(struct page *page, enum pt_level level)
544 unsigned pgfl = TestSetPagePinned(page);
548 flush = 0; /* already pinned */
549 else if (PageHighMem(page))
550 /* kmaps need flushing if we found an unpinned
554 void *pt = lowmem_page_address(page);
555 unsigned long pfn = page_to_pfn(page);
556 struct multicall_space mcs = __xen_mc_entry(0);
563 ptl = lock_pte(page);
565 MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
566 pfn_pte(pfn, PAGE_KERNEL_RO),
567 level == PT_PGD ? UVMF_TLB_FLUSH : 0);
570 xen_do_pin(MMUEXT_PIN_L1_TABLE, pfn);
573 /* Queue a deferred unlock for when this batch
575 xen_mc_callback(do_unlock, ptl);
582 /* This is called just after a mm has been created, but it has not
583 been used yet. We need to make sure that its pagetable is all
584 read-only, and can be pinned. */
585 void xen_pgd_pin(pgd_t *pgd)
589 if (pgd_walk(pgd, pin_page, TASK_SIZE)) {
590 /* re-enable interrupts for kmap_flush_unused */
596 xen_do_pin(MMUEXT_PIN_L3_TABLE, PFN_DOWN(__pa(pgd)));
601 * On save, we need to pin all pagetables to make sure they get their
602 * mfns turned into pfns. Search the list for any unpinned pgds and pin
603 * them (unpinned pgds are not currently in use, probably because the
604 * process is under construction or destruction).
606 void xen_mm_pin_all(void)
611 spin_lock_irqsave(&pgd_lock, flags);
613 list_for_each_entry(page, &pgd_list, lru) {
614 if (!PagePinned(page)) {
615 xen_pgd_pin((pgd_t *)page_address(page));
616 SetPageSavePinned(page);
620 spin_unlock_irqrestore(&pgd_lock, flags);
623 /* The init_mm pagetable is really pinned as soon as its created, but
624 that's before we have page structures to store the bits. So do all
625 the book-keeping now. */
626 static __init int mark_pinned(struct page *page, enum pt_level level)
632 void __init xen_mark_init_mm_pinned(void)
634 pgd_walk(init_mm.pgd, mark_pinned, FIXADDR_TOP);
637 static int unpin_page(struct page *page, enum pt_level level)
639 unsigned pgfl = TestClearPagePinned(page);
641 if (pgfl && !PageHighMem(page)) {
642 void *pt = lowmem_page_address(page);
643 unsigned long pfn = page_to_pfn(page);
644 spinlock_t *ptl = NULL;
645 struct multicall_space mcs;
647 if (level == PT_PTE) {
648 ptl = lock_pte(page);
650 xen_do_pin(MMUEXT_UNPIN_TABLE, pfn);
653 mcs = __xen_mc_entry(0);
655 MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
656 pfn_pte(pfn, PAGE_KERNEL),
657 level == PT_PGD ? UVMF_TLB_FLUSH : 0);
660 /* unlock when batch completed */
661 xen_mc_callback(do_unlock, ptl);
665 return 0; /* never need to flush on unpin */
668 /* Release a pagetables pages back as normal RW */
669 static void xen_pgd_unpin(pgd_t *pgd)
673 xen_do_pin(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));
675 pgd_walk(pgd, unpin_page, TASK_SIZE);
681 * On resume, undo any pinning done at save, so that the rest of the
682 * kernel doesn't see any unexpected pinned pagetables.
684 void xen_mm_unpin_all(void)
689 spin_lock_irqsave(&pgd_lock, flags);
691 list_for_each_entry(page, &pgd_list, lru) {
692 if (PageSavePinned(page)) {
693 BUG_ON(!PagePinned(page));
694 printk("unpinning pinned %p\n", page_address(page));
695 xen_pgd_unpin((pgd_t *)page_address(page));
696 ClearPageSavePinned(page);
700 spin_unlock_irqrestore(&pgd_lock, flags);
703 void xen_activate_mm(struct mm_struct *prev, struct mm_struct *next)
705 spin_lock(&next->page_table_lock);
706 xen_pgd_pin(next->pgd);
707 spin_unlock(&next->page_table_lock);
710 void xen_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
712 spin_lock(&mm->page_table_lock);
713 xen_pgd_pin(mm->pgd);
714 spin_unlock(&mm->page_table_lock);
719 /* Another cpu may still have their %cr3 pointing at the pagetable, so
720 we need to repoint it somewhere else before we can unpin it. */
721 static void drop_other_mm_ref(void *info)
723 struct mm_struct *mm = info;
725 if (__get_cpu_var(cpu_tlbstate).active_mm == mm)
726 leave_mm(smp_processor_id());
728 /* If this cpu still has a stale cr3 reference, then make sure
729 it has been flushed. */
730 if (x86_read_percpu(xen_current_cr3) == __pa(mm->pgd)) {
731 load_cr3(swapper_pg_dir);
732 arch_flush_lazy_cpu_mode();
736 static void drop_mm_ref(struct mm_struct *mm)
741 if (current->active_mm == mm) {
742 if (current->mm == mm)
743 load_cr3(swapper_pg_dir);
745 leave_mm(smp_processor_id());
746 arch_flush_lazy_cpu_mode();
749 /* Get the "official" set of cpus referring to our pagetable. */
750 mask = mm->cpu_vm_mask;
752 /* It's possible that a vcpu may have a stale reference to our
753 cr3, because its in lazy mode, and it hasn't yet flushed
754 its set of pending hypercalls yet. In this case, we can
755 look at its actual current cr3 value, and force it to flush
757 for_each_online_cpu(cpu) {
758 if (per_cpu(xen_current_cr3, cpu) == __pa(mm->pgd))
762 if (!cpus_empty(mask))
763 xen_smp_call_function_mask(mask, drop_other_mm_ref, mm, 1);
766 static void drop_mm_ref(struct mm_struct *mm)
768 if (current->active_mm == mm)
769 load_cr3(swapper_pg_dir);
774 * While a process runs, Xen pins its pagetables, which means that the
775 * hypervisor forces it to be read-only, and it controls all updates
776 * to it. This means that all pagetable updates have to go via the
777 * hypervisor, which is moderately expensive.
779 * Since we're pulling the pagetable down, we switch to use init_mm,
780 * unpin old process pagetable and mark it all read-write, which
781 * allows further operations on it to be simple memory accesses.
783 * The only subtle point is that another CPU may be still using the
784 * pagetable because of lazy tlb flushing. This means we need need to
785 * switch all CPUs off this pagetable before we can unpin it.
787 void xen_exit_mmap(struct mm_struct *mm)
789 get_cpu(); /* make sure we don't move around */
793 spin_lock(&mm->page_table_lock);
795 /* pgd may not be pinned in the error exit path of execve */
796 if (page_pinned(mm->pgd))
797 xen_pgd_unpin(mm->pgd);
799 spin_unlock(&mm->page_table_lock);