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 xmaddr_t arbitrary_virt_to_machine(unsigned long address)
62 pte_t *pte = lookup_address(address, &level);
63 unsigned offset = address & PAGE_MASK;
67 return XMADDR((pte_mfn(*pte) << PAGE_SHIFT) + offset);
70 void make_lowmem_page_readonly(void *vaddr)
73 unsigned long address = (unsigned long)vaddr;
76 pte = lookup_address(address, &level);
79 ptev = pte_wrprotect(*pte);
81 if (HYPERVISOR_update_va_mapping(address, ptev, 0))
85 void make_lowmem_page_readwrite(void *vaddr)
88 unsigned long address = (unsigned long)vaddr;
91 pte = lookup_address(address, &level);
94 ptev = pte_mkwrite(*pte);
96 if (HYPERVISOR_update_va_mapping(address, ptev, 0))
101 void xen_set_pmd(pmd_t *ptr, pmd_t val)
103 struct multicall_space mcs;
104 struct mmu_update *u;
108 mcs = xen_mc_entry(sizeof(*u));
110 u->ptr = virt_to_machine(ptr).maddr;
111 u->val = pmd_val_ma(val);
112 MULTI_mmu_update(mcs.mc, u, 1, NULL, DOMID_SELF);
114 xen_mc_issue(PARAVIRT_LAZY_MMU);
120 * Associate a virtual page frame with a given physical page frame
121 * and protection flags for that frame.
123 void set_pte_mfn(unsigned long vaddr, unsigned long mfn, pgprot_t flags)
130 pgd = swapper_pg_dir + pgd_index(vaddr);
131 if (pgd_none(*pgd)) {
135 pud = pud_offset(pgd, vaddr);
136 if (pud_none(*pud)) {
140 pmd = pmd_offset(pud, vaddr);
141 if (pmd_none(*pmd)) {
145 pte = pte_offset_kernel(pmd, vaddr);
146 /* <mfn,flags> stored as-is, to permit clearing entries */
147 xen_set_pte(pte, mfn_pte(mfn, flags));
150 * It's enough to flush this one mapping.
151 * (PGE mappings get flushed as well)
153 __flush_tlb_one(vaddr);
156 void xen_set_pte_at(struct mm_struct *mm, unsigned long addr,
157 pte_t *ptep, pte_t pteval)
159 /* updates to init_mm may be done without lock */
163 if (mm == current->mm || mm == &init_mm) {
164 if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
165 struct multicall_space mcs;
166 mcs = xen_mc_entry(0);
168 MULTI_update_va_mapping(mcs.mc, addr, pteval, 0);
169 xen_mc_issue(PARAVIRT_LAZY_MMU);
172 if (HYPERVISOR_update_va_mapping(addr, pteval, 0) == 0)
175 xen_set_pte(ptep, pteval);
182 pteval_t xen_pte_val(pte_t pte)
184 pteval_t ret = pte.pte;
186 if (ret & _PAGE_PRESENT)
187 ret = machine_to_phys(XMADDR(ret)).paddr | _PAGE_PRESENT;
192 pgdval_t xen_pgd_val(pgd_t pgd)
194 pgdval_t ret = pgd.pgd;
195 if (ret & _PAGE_PRESENT)
196 ret = machine_to_phys(XMADDR(ret)).paddr | _PAGE_PRESENT;
200 pte_t xen_make_pte(pteval_t pte)
202 if (pte & _PAGE_PRESENT) {
203 pte = phys_to_machine(XPADDR(pte)).maddr;
204 pte &= ~(_PAGE_PCD | _PAGE_PWT);
207 return (pte_t){ .pte = pte };
210 pgd_t xen_make_pgd(pgdval_t pgd)
212 if (pgd & _PAGE_PRESENT)
213 pgd = phys_to_machine(XPADDR(pgd)).maddr;
215 return (pgd_t){ pgd };
218 pmdval_t xen_pmd_val(pmd_t pmd)
220 pmdval_t ret = native_pmd_val(pmd);
221 if (ret & _PAGE_PRESENT)
222 ret = machine_to_phys(XMADDR(ret)).paddr | _PAGE_PRESENT;
226 void xen_set_pud(pud_t *ptr, pud_t val)
228 struct multicall_space mcs;
229 struct mmu_update *u;
233 mcs = xen_mc_entry(sizeof(*u));
235 u->ptr = virt_to_machine(ptr).maddr;
236 u->val = pud_val_ma(val);
237 MULTI_mmu_update(mcs.mc, u, 1, NULL, DOMID_SELF);
239 xen_mc_issue(PARAVIRT_LAZY_MMU);
244 void xen_set_pte(pte_t *ptep, pte_t pte)
246 ptep->pte_high = pte.pte_high;
248 ptep->pte_low = pte.pte_low;
251 void xen_set_pte_atomic(pte_t *ptep, pte_t pte)
253 set_64bit((u64 *)ptep, pte_val_ma(pte));
256 void xen_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
259 smp_wmb(); /* make sure low gets written first */
263 void xen_pmd_clear(pmd_t *pmdp)
265 xen_set_pmd(pmdp, __pmd(0));
268 pmd_t xen_make_pmd(pmdval_t pmd)
270 if (pmd & _PAGE_PRESENT)
271 pmd = phys_to_machine(XPADDR(pmd)).maddr;
273 return native_make_pmd(pmd);
277 (Yet another) pagetable walker. This one is intended for pinning a
278 pagetable. This means that it walks a pagetable and calls the
279 callback function on each page it finds making up the page table,
280 at every level. It walks the entire pagetable, but it only bothers
281 pinning pte pages which are below pte_limit. In the normal case
282 this will be TASK_SIZE, but at boot we need to pin up to
283 FIXADDR_TOP. But the important bit is that we don't pin beyond
284 there, because then we start getting into Xen's ptes.
286 static int pgd_walk(pgd_t *pgd_base, int (*func)(struct page *, enum pt_level),
289 pgd_t *pgd = pgd_base;
291 unsigned long addr = 0;
292 unsigned long pgd_next;
294 BUG_ON(limit > FIXADDR_TOP);
296 if (xen_feature(XENFEAT_auto_translated_physmap))
299 for (; addr != FIXADDR_TOP; pgd++, addr = pgd_next) {
301 unsigned long pud_limit, pud_next;
303 pgd_next = pud_limit = pgd_addr_end(addr, FIXADDR_TOP);
308 pud = pud_offset(pgd, 0);
310 if (PTRS_PER_PUD > 1) /* not folded */
311 flush |= (*func)(virt_to_page(pud), PT_PUD);
313 for (; addr != pud_limit; pud++, addr = pud_next) {
315 unsigned long pmd_limit;
317 pud_next = pud_addr_end(addr, pud_limit);
319 if (pud_next < limit)
320 pmd_limit = pud_next;
327 pmd = pmd_offset(pud, 0);
329 if (PTRS_PER_PMD > 1) /* not folded */
330 flush |= (*func)(virt_to_page(pmd), PT_PMD);
332 for (; addr != pmd_limit; pmd++) {
333 addr += (PAGE_SIZE * PTRS_PER_PTE);
334 if ((pmd_limit-1) < (addr-1)) {
342 flush |= (*func)(pmd_page(*pmd), PT_PTE);
347 flush |= (*func)(virt_to_page(pgd_base), PT_PGD);
352 static spinlock_t *lock_pte(struct page *page)
354 spinlock_t *ptl = NULL;
356 #if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
357 ptl = __pte_lockptr(page);
364 static void do_unlock(void *v)
370 static void xen_do_pin(unsigned level, unsigned long pfn)
372 struct mmuext_op *op;
373 struct multicall_space mcs;
375 mcs = __xen_mc_entry(sizeof(*op));
378 op->arg1.mfn = pfn_to_mfn(pfn);
379 MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
382 static int pin_page(struct page *page, enum pt_level level)
384 unsigned pgfl = TestSetPagePinned(page);
388 flush = 0; /* already pinned */
389 else if (PageHighMem(page))
390 /* kmaps need flushing if we found an unpinned
394 void *pt = lowmem_page_address(page);
395 unsigned long pfn = page_to_pfn(page);
396 struct multicall_space mcs = __xen_mc_entry(0);
403 ptl = lock_pte(page);
405 MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
406 pfn_pte(pfn, PAGE_KERNEL_RO),
407 level == PT_PGD ? UVMF_TLB_FLUSH : 0);
410 xen_do_pin(MMUEXT_PIN_L1_TABLE, pfn);
413 /* Queue a deferred unlock for when this batch
415 xen_mc_callback(do_unlock, ptl);
422 /* This is called just after a mm has been created, but it has not
423 been used yet. We need to make sure that its pagetable is all
424 read-only, and can be pinned. */
425 void xen_pgd_pin(pgd_t *pgd)
429 if (pgd_walk(pgd, pin_page, TASK_SIZE)) {
430 /* re-enable interrupts for kmap_flush_unused */
436 xen_do_pin(MMUEXT_PIN_L3_TABLE, PFN_DOWN(__pa(pgd)));
440 /* The init_mm pagetable is really pinned as soon as its created, but
441 that's before we have page structures to store the bits. So do all
442 the book-keeping now. */
443 static __init int mark_pinned(struct page *page, enum pt_level level)
449 void __init xen_mark_init_mm_pinned(void)
451 pgd_walk(init_mm.pgd, mark_pinned, FIXADDR_TOP);
454 static int unpin_page(struct page *page, enum pt_level level)
456 unsigned pgfl = TestClearPagePinned(page);
458 if (pgfl && !PageHighMem(page)) {
459 void *pt = lowmem_page_address(page);
460 unsigned long pfn = page_to_pfn(page);
461 spinlock_t *ptl = NULL;
462 struct multicall_space mcs;
464 if (level == PT_PTE) {
465 ptl = lock_pte(page);
467 xen_do_pin(MMUEXT_UNPIN_TABLE, pfn);
470 mcs = __xen_mc_entry(0);
472 MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
473 pfn_pte(pfn, PAGE_KERNEL),
474 level == PT_PGD ? UVMF_TLB_FLUSH : 0);
477 /* unlock when batch completed */
478 xen_mc_callback(do_unlock, ptl);
482 return 0; /* never need to flush on unpin */
485 /* Release a pagetables pages back as normal RW */
486 static void xen_pgd_unpin(pgd_t *pgd)
490 xen_do_pin(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));
492 pgd_walk(pgd, unpin_page, TASK_SIZE);
497 void xen_activate_mm(struct mm_struct *prev, struct mm_struct *next)
499 spin_lock(&next->page_table_lock);
500 xen_pgd_pin(next->pgd);
501 spin_unlock(&next->page_table_lock);
504 void xen_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
506 spin_lock(&mm->page_table_lock);
507 xen_pgd_pin(mm->pgd);
508 spin_unlock(&mm->page_table_lock);
513 /* Another cpu may still have their %cr3 pointing at the pagetable, so
514 we need to repoint it somewhere else before we can unpin it. */
515 static void drop_other_mm_ref(void *info)
517 struct mm_struct *mm = info;
519 if (__get_cpu_var(cpu_tlbstate).active_mm == mm)
520 leave_mm(smp_processor_id());
522 /* If this cpu still has a stale cr3 reference, then make sure
523 it has been flushed. */
524 if (x86_read_percpu(xen_current_cr3) == __pa(mm->pgd)) {
525 load_cr3(swapper_pg_dir);
526 arch_flush_lazy_cpu_mode();
530 static void drop_mm_ref(struct mm_struct *mm)
535 if (current->active_mm == mm) {
536 if (current->mm == mm)
537 load_cr3(swapper_pg_dir);
539 leave_mm(smp_processor_id());
540 arch_flush_lazy_cpu_mode();
543 /* Get the "official" set of cpus referring to our pagetable. */
544 mask = mm->cpu_vm_mask;
546 /* It's possible that a vcpu may have a stale reference to our
547 cr3, because its in lazy mode, and it hasn't yet flushed
548 its set of pending hypercalls yet. In this case, we can
549 look at its actual current cr3 value, and force it to flush
551 for_each_online_cpu(cpu) {
552 if (per_cpu(xen_current_cr3, cpu) == __pa(mm->pgd))
556 if (!cpus_empty(mask))
557 xen_smp_call_function_mask(mask, drop_other_mm_ref, mm, 1);
560 static void drop_mm_ref(struct mm_struct *mm)
562 if (current->active_mm == mm)
563 load_cr3(swapper_pg_dir);
568 * While a process runs, Xen pins its pagetables, which means that the
569 * hypervisor forces it to be read-only, and it controls all updates
570 * to it. This means that all pagetable updates have to go via the
571 * hypervisor, which is moderately expensive.
573 * Since we're pulling the pagetable down, we switch to use init_mm,
574 * unpin old process pagetable and mark it all read-write, which
575 * allows further operations on it to be simple memory accesses.
577 * The only subtle point is that another CPU may be still using the
578 * pagetable because of lazy tlb flushing. This means we need need to
579 * switch all CPUs off this pagetable before we can unpin it.
581 void xen_exit_mmap(struct mm_struct *mm)
583 get_cpu(); /* make sure we don't move around */
587 spin_lock(&mm->page_table_lock);
589 /* pgd may not be pinned in the error exit path of execve */
590 if (PagePinned(virt_to_page(mm->pgd)))
591 xen_pgd_unpin(mm->pgd);
593 spin_unlock(&mm->page_table_lock);