arch/x86/xen/p2m.c - kernel/msm-4.9 - Gitiles

 /*
  * Xen leaves the responsibility for maintaining p2m mappings to the
  * guests themselves, but it must also access and update the p2m array
  * during suspend/resume when all the pages are reallocated.
  *
  * The logical flat p2m table is mapped to a linear kernel memory area.
  * For accesses by Xen a three-level tree linked via mfns only is set up to
  * allow the address space to be sparse.
  *
  *               Xen
  *                |
  *          p2m_top_mfn
  *              /   \
  * p2m_mid_mfn p2m_mid_mfn
  *         /           /
  *  p2m p2m p2m ...
  *
  * The p2m_mid_mfn pages are mapped by p2m_top_mfn_p.
  *
  * The p2m_top_mfn level is limited to 1 page, so the maximum representable
  * pseudo-physical address space is:
  *  P2M_TOP_PER_PAGE * P2M_MID_PER_PAGE * P2M_PER_PAGE pages
  *
  * P2M_PER_PAGE depends on the architecture, as a mfn is always
  * unsigned long (8 bytes on 64-bit, 4 bytes on 32), leading to
  * 512 and 1024 entries respectively.
  *
  * In short, these structures contain the Machine Frame Number (MFN) of the PFN.
  *
  * However not all entries are filled with MFNs. Specifically for all other
  * leaf entries, or for the top  root, or middle one, for which there is a void
  * entry, we assume it is  "missing". So (for example)
  *  pfn_to_mfn(0x90909090)=INVALID_P2M_ENTRY.
  * We have a dedicated page p2m_missing with all entries being
  * INVALID_P2M_ENTRY. This page may be referenced multiple times in the p2m
  * list/tree in case there are multiple areas with P2M_PER_PAGE invalid pfns.
  *
  * We also have the possibility of setting 1-1 mappings on certain regions, so
  * that:
  *  pfn_to_mfn(0xc0000)=0xc0000
  *
  * The benefit of this is, that we can assume for non-RAM regions (think
  * PCI BARs, or ACPI spaces), we can create mappings easily because we
  * get the PFN value to match the MFN.
  *
  * For this to work efficiently we have one new page p2m_identity. All entries
  * in p2m_identity are set to INVALID_P2M_ENTRY type (Xen toolstack only
  * recognizes that and MFNs, no other fancy value).
  *
  * On lookup we spot that the entry points to p2m_identity and return the
  * identity value instead of dereferencing and returning INVALID_P2M_ENTRY.
  * If the entry points to an allocated page, we just proceed as before and
  * return the PFN. If the PFN has IDENTITY_FRAME_BIT set we unmask that in
  * appropriate functions (pfn_to_mfn).
  *
  * The reason for having the IDENTITY_FRAME_BIT instead of just returning the
  * PFN is that we could find ourselves where pfn_to_mfn(pfn)==pfn for a
  * non-identity pfn. To protect ourselves against we elect to set (and get) the
  * IDENTITY_FRAME_BIT on all identity mapped PFNs.
  */

 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/list.h>
 #include <linux/hash.h>
 #include <linux/sched.h>
 #include <linux/seq_file.h>
 #include <linux/bootmem.h>
 #include <linux/slab.h>

 #include <asm/cache.h>
 #include <asm/setup.h>
 #include <asm/uaccess.h>

 #include <asm/xen/page.h>
 #include <asm/xen/hypercall.h>
 #include <asm/xen/hypervisor.h>
 #include <xen/balloon.h>
 #include <xen/grant_table.h>

 #include "p2m.h"
 #include "multicalls.h"
 #include "xen-ops.h"

 #define PMDS_PER_MID_PAGE	(P2M_MID_PER_PAGE / PTRS_PER_PTE)

 unsigned long *xen_p2m_addr __read_mostly;
 EXPORT_SYMBOL_GPL(xen_p2m_addr);
 unsigned long xen_p2m_size __read_mostly;
 EXPORT_SYMBOL_GPL(xen_p2m_size);
 unsigned long xen_max_p2m_pfn __read_mostly;
 EXPORT_SYMBOL_GPL(xen_max_p2m_pfn);

 static DEFINE_SPINLOCK(p2m_update_lock);

 static unsigned long *p2m_mid_missing_mfn;
 static unsigned long *p2m_top_mfn;
 static unsigned long **p2m_top_mfn_p;
 static unsigned long *p2m_missing;
 static unsigned long *p2m_identity;
 static pte_t *p2m_missing_pte;
 static pte_t *p2m_identity_pte;

 static inline unsigned p2m_top_index(unsigned long pfn)
 {
 	BUG_ON(pfn >= MAX_P2M_PFN);
 	return pfn / (P2M_MID_PER_PAGE * P2M_PER_PAGE);
 }

 static inline unsigned p2m_mid_index(unsigned long pfn)
 {
 	return (pfn / P2M_PER_PAGE) % P2M_MID_PER_PAGE;
 }

 static inline unsigned p2m_index(unsigned long pfn)
 {
 	return pfn % P2M_PER_PAGE;
 }

 static void p2m_top_mfn_init(unsigned long *top)
 {
 	unsigned i;

 	for (i = 0; i < P2M_TOP_PER_PAGE; i++)
 		top[i] = virt_to_mfn(p2m_mid_missing_mfn);
 }

 static void p2m_top_mfn_p_init(unsigned long **top)
 {
 	unsigned i;

 	for (i = 0; i < P2M_TOP_PER_PAGE; i++)
 		top[i] = p2m_mid_missing_mfn;
 }

 static void p2m_mid_mfn_init(unsigned long *mid, unsigned long *leaf)
 {
 	unsigned i;

 	for (i = 0; i < P2M_MID_PER_PAGE; i++)
 		mid[i] = virt_to_mfn(leaf);
 }

 static void p2m_init(unsigned long *p2m)
 {
 	unsigned i;

 	for (i = 0; i < P2M_PER_PAGE; i++)
 		p2m[i] = INVALID_P2M_ENTRY;
 }

 static void p2m_init_identity(unsigned long *p2m, unsigned long pfn)
 {
 	unsigned i;

 	for (i = 0; i < P2M_PER_PAGE; i++)
 		p2m[i] = IDENTITY_FRAME(pfn + i);
 }

 static void * __ref alloc_p2m_page(void)
 {
 	if (unlikely(!slab_is_available()))
 		return alloc_bootmem_align(PAGE_SIZE, PAGE_SIZE);

 	return (void *)__get_free_page(GFP_KERNEL | __GFP_REPEAT);
 }

 static void __ref free_p2m_page(void *p)
 {
 	if (unlikely(!slab_is_available())) {
 		free_bootmem((unsigned long)p, PAGE_SIZE);
 		return;
 	}

 	free_page((unsigned long)p);
 }

 /*
  * Build the parallel p2m_top_mfn and p2m_mid_mfn structures
  *
  * This is called both at boot time, and after resuming from suspend:
  * - At boot time we're called rather early, and must use alloc_bootmem*()
  *   to allocate memory.
  *
  * - After resume we're called from within stop_machine, but the mfn
  *   tree should already be completely allocated.
  */
 void __ref xen_build_mfn_list_list(void)
 {
 	unsigned long pfn, mfn;
 	pte_t *ptep;
 	unsigned int level, topidx, mididx;
 	unsigned long *mid_mfn_p;

 	if (xen_feature(XENFEAT_auto_translated_physmap))
 		return;

 	/* Pre-initialize p2m_top_mfn to be completely missing */
 	if (p2m_top_mfn == NULL) {
 		p2m_mid_missing_mfn = alloc_p2m_page();
 		p2m_mid_mfn_init(p2m_mid_missing_mfn, p2m_missing);

 		p2m_top_mfn_p = alloc_p2m_page();
 		p2m_top_mfn_p_init(p2m_top_mfn_p);

 		p2m_top_mfn = alloc_p2m_page();
 		p2m_top_mfn_init(p2m_top_mfn);
 	} else {
 		/* Reinitialise, mfn's all change after migration */
 		p2m_mid_mfn_init(p2m_mid_missing_mfn, p2m_missing);
 	}

 	for (pfn = 0; pfn < xen_max_p2m_pfn && pfn < MAX_P2M_PFN;
 	     pfn += P2M_PER_PAGE) {
 		topidx = p2m_top_index(pfn);
 		mididx = p2m_mid_index(pfn);

 		mid_mfn_p = p2m_top_mfn_p[topidx];
 		ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn),
 				      &level);
 		BUG_ON(!ptep || level != PG_LEVEL_4K);
 		mfn = pte_mfn(*ptep);
 		ptep = (pte_t *)((unsigned long)ptep & ~(PAGE_SIZE - 1));

 		/* Don't bother allocating any mfn mid levels if
 		 * they're just missing, just update the stored mfn,
 		 * since all could have changed over a migrate.
 		 */
 		if (ptep == p2m_missing_pte || ptep == p2m_identity_pte) {
 			BUG_ON(mididx);
 			BUG_ON(mid_mfn_p != p2m_mid_missing_mfn);
 			p2m_top_mfn[topidx] = virt_to_mfn(p2m_mid_missing_mfn);
 			pfn += (P2M_MID_PER_PAGE - 1) * P2M_PER_PAGE;
 			continue;
 		}

 		if (mid_mfn_p == p2m_mid_missing_mfn) {
 			mid_mfn_p = alloc_p2m_page();
 			p2m_mid_mfn_init(mid_mfn_p, p2m_missing);

 			p2m_top_mfn_p[topidx] = mid_mfn_p;
 		}

 		p2m_top_mfn[topidx] = virt_to_mfn(mid_mfn_p);
 		mid_mfn_p[mididx] = mfn;
 	}
 }

 void xen_setup_mfn_list_list(void)
 {
 	if (xen_feature(XENFEAT_auto_translated_physmap))
 		return;

 	BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);

 	HYPERVISOR_shared_info->arch.pfn_to_mfn_frame_list_list =
 		virt_to_mfn(p2m_top_mfn);
 	HYPERVISOR_shared_info->arch.max_pfn = xen_max_p2m_pfn;
 }

 /* Set up p2m_top to point to the domain-builder provided p2m pages */
 void __init xen_build_dynamic_phys_to_machine(void)
 {
 	unsigned long pfn;

 	 if (xen_feature(XENFEAT_auto_translated_physmap))
 		return;

 	xen_p2m_addr = (unsigned long *)xen_start_info->mfn_list;
 	xen_p2m_size = ALIGN(xen_start_info->nr_pages, P2M_PER_PAGE);

 	for (pfn = xen_start_info->nr_pages; pfn < xen_p2m_size; pfn++)
 		xen_p2m_addr[pfn] = INVALID_P2M_ENTRY;

 	xen_max_p2m_pfn = xen_p2m_size;
 }

 #define P2M_TYPE_IDENTITY	0
 #define P2M_TYPE_MISSING	1
 #define P2M_TYPE_PFN		2
 #define P2M_TYPE_UNKNOWN	3

 static int xen_p2m_elem_type(unsigned long pfn)
 {
 	unsigned long mfn;

 	if (pfn >= xen_p2m_size)
 		return P2M_TYPE_IDENTITY;

 	mfn = xen_p2m_addr[pfn];

 	if (mfn == INVALID_P2M_ENTRY)
 		return P2M_TYPE_MISSING;

 	if (mfn & IDENTITY_FRAME_BIT)
 		return P2M_TYPE_IDENTITY;

 	return P2M_TYPE_PFN;
 }

 static void __init xen_rebuild_p2m_list(unsigned long *p2m)
 {
 	unsigned int i, chunk;
 	unsigned long pfn;
 	unsigned long *mfns;
 	pte_t *ptep;
 	pmd_t *pmdp;
 	int type;

 	p2m_missing = alloc_p2m_page();
 	p2m_init(p2m_missing);
 	p2m_identity = alloc_p2m_page();
 	p2m_init(p2m_identity);

 	p2m_missing_pte = alloc_p2m_page();
 	paravirt_alloc_pte(&init_mm, __pa(p2m_missing_pte) >> PAGE_SHIFT);
 	p2m_identity_pte = alloc_p2m_page();
 	paravirt_alloc_pte(&init_mm, __pa(p2m_identity_pte) >> PAGE_SHIFT);
 	for (i = 0; i < PTRS_PER_PTE; i++) {
 		set_pte(p2m_missing_pte + i,
 			pfn_pte(PFN_DOWN(__pa(p2m_missing)), PAGE_KERNEL_RO));
 		set_pte(p2m_identity_pte + i,
 			pfn_pte(PFN_DOWN(__pa(p2m_identity)), PAGE_KERNEL_RO));
 	}

 	for (pfn = 0; pfn < xen_max_p2m_pfn; pfn += chunk) {
 		/*
 		 * Try to map missing/identity PMDs or p2m-pages if possible.
 		 * We have to respect the structure of the mfn_list_list
 		 * which will be built just afterwards.
 		 * Chunk size to test is one p2m page if we are in the middle
 		 * of a mfn_list_list mid page and the complete mid page area
 		 * if we are at index 0 of the mid page. Please note that a
 		 * mid page might cover more than one PMD, e.g. on 32 bit PAE
 		 * kernels.
 		 */
 		chunk = (pfn & (P2M_PER_PAGE * P2M_MID_PER_PAGE - 1)) ?
 			P2M_PER_PAGE : P2M_PER_PAGE * P2M_MID_PER_PAGE;

 		type = xen_p2m_elem_type(pfn);
 		i = 0;
 		if (type != P2M_TYPE_PFN)
 			for (i = 1; i < chunk; i++)
 				if (xen_p2m_elem_type(pfn + i) != type)
 					break;
 		if (i < chunk)
 			/* Reset to minimal chunk size. */
 			chunk = P2M_PER_PAGE;

 		if (type == P2M_TYPE_PFN || i < chunk) {
 			/* Use initial p2m page contents. */
 #ifdef CONFIG_X86_64
 			mfns = alloc_p2m_page();
 			copy_page(mfns, xen_p2m_addr + pfn);
 #else
 			mfns = xen_p2m_addr + pfn;
 #endif
 			ptep = populate_extra_pte((unsigned long)(p2m + pfn));
 			set_pte(ptep,
 				pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL));
 			continue;
 		}

 		if (chunk == P2M_PER_PAGE) {
 			/* Map complete missing or identity p2m-page. */
 			mfns = (type == P2M_TYPE_MISSING) ?
 				p2m_missing : p2m_identity;
 			ptep = populate_extra_pte((unsigned long)(p2m + pfn));
 			set_pte(ptep,
 				pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL_RO));
 			continue;
 		}

 		/* Complete missing or identity PMD(s) can be mapped. */
 		ptep = (type == P2M_TYPE_MISSING) ?
 			p2m_missing_pte : p2m_identity_pte;
 		for (i = 0; i < PMDS_PER_MID_PAGE; i++) {
 			pmdp = populate_extra_pmd(
 				(unsigned long)(p2m + pfn) + i * PMD_SIZE);
 			set_pmd(pmdp, __pmd(__pa(ptep) | _KERNPG_TABLE));
 		}
 	}
 }

 void __init xen_vmalloc_p2m_tree(void)
 {
 	static struct vm_struct vm;

 	vm.flags = VM_ALLOC;
 	vm.size = ALIGN(sizeof(unsigned long) * xen_max_p2m_pfn,
 			PMD_SIZE * PMDS_PER_MID_PAGE);
 	vm_area_register_early(&vm, PMD_SIZE * PMDS_PER_MID_PAGE);
 	pr_notice("p2m virtual area at %p, size is %lx\n", vm.addr, vm.size);

 	xen_max_p2m_pfn = vm.size / sizeof(unsigned long);

 	xen_rebuild_p2m_list(vm.addr);

 	xen_p2m_addr = vm.addr;
 	xen_p2m_size = xen_max_p2m_pfn;

 	xen_inv_extra_mem();
 }

 unsigned long get_phys_to_machine(unsigned long pfn)
 {
 	pte_t *ptep;
 	unsigned int level;

 	if (unlikely(pfn >= xen_p2m_size)) {
 		if (pfn < xen_max_p2m_pfn)
 			return xen_chk_extra_mem(pfn);

 		return IDENTITY_FRAME(pfn);
 	}

 	ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn), &level);
 	BUG_ON(!ptep || level != PG_LEVEL_4K);

 	/*
 	 * The INVALID_P2M_ENTRY is filled in both p2m_*identity
 	 * and in p2m_*missing, so returning the INVALID_P2M_ENTRY
 	 * would be wrong.
 	 */
 	if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_identity)))
 		return IDENTITY_FRAME(pfn);

 	return xen_p2m_addr[pfn];
 }
 EXPORT_SYMBOL_GPL(get_phys_to_machine);

 /*
  * Allocate new pmd(s). It is checked whether the old pmd is still in place.
  * If not, nothing is changed. This is okay as the only reason for allocating
  * a new pmd is to replace p2m_missing_pte or p2m_identity_pte by a individual
  * pmd. In case of PAE/x86-32 there are multiple pmds to allocate!
  */
 static pte_t *alloc_p2m_pmd(unsigned long addr, pte_t *pte_pg)
 {
 	pte_t *ptechk;
 	pte_t *pte_newpg[PMDS_PER_MID_PAGE];
 	pmd_t *pmdp;
 	unsigned int level;
 	unsigned long flags;
 	unsigned long vaddr;
 	int i;

 	/* Do all allocations first to bail out in error case. */
 	for (i = 0; i < PMDS_PER_MID_PAGE; i++) {
 		pte_newpg[i] = alloc_p2m_page();
 		if (!pte_newpg[i]) {
 			for (i--; i >= 0; i--)
 				free_p2m_page(pte_newpg[i]);

 			return NULL;
 		}
 	}

 	vaddr = addr & ~(PMD_SIZE * PMDS_PER_MID_PAGE - 1);

 	for (i = 0; i < PMDS_PER_MID_PAGE; i++) {
 		copy_page(pte_newpg[i], pte_pg);
 		paravirt_alloc_pte(&init_mm, __pa(pte_newpg[i]) >> PAGE_SHIFT);

 		pmdp = lookup_pmd_address(vaddr);
 		BUG_ON(!pmdp);

 		spin_lock_irqsave(&p2m_update_lock, flags);

 		ptechk = lookup_address(vaddr, &level);
 		if (ptechk == pte_pg) {
 			set_pmd(pmdp,
 				__pmd(__pa(pte_newpg[i]) | _KERNPG_TABLE));
 			pte_newpg[i] = NULL;
 		}

 		spin_unlock_irqrestore(&p2m_update_lock, flags);

 		if (pte_newpg[i]) {
 			paravirt_release_pte(__pa(pte_newpg[i]) >> PAGE_SHIFT);
 			free_p2m_page(pte_newpg[i]);
 		}

 		vaddr += PMD_SIZE;
 	}

 	return lookup_address(addr, &level);
 }

 /*
  * Fully allocate the p2m structure for a given pfn.  We need to check
  * that both the top and mid levels are allocated, and make sure the
  * parallel mfn tree is kept in sync.  We may race with other cpus, so
  * the new pages are installed with cmpxchg; if we lose the race then
  * simply free the page we allocated and use the one that's there.
  */
 static bool alloc_p2m(unsigned long pfn)
 {
 	unsigned topidx, mididx;
 	unsigned long *top_mfn_p, *mid_mfn;
 	pte_t *ptep, *pte_pg;
 	unsigned int level;
 	unsigned long flags;
 	unsigned long addr = (unsigned long)(xen_p2m_addr + pfn);
 	unsigned long p2m_pfn;

 	topidx = p2m_top_index(pfn);
 	mididx = p2m_mid_index(pfn);

 	ptep = lookup_address(addr, &level);
 	BUG_ON(!ptep || level != PG_LEVEL_4K);
 	pte_pg = (pte_t *)((unsigned long)ptep & ~(PAGE_SIZE - 1));

 	if (pte_pg == p2m_missing_pte || pte_pg == p2m_identity_pte) {
 		/* PMD level is missing, allocate a new one */
 		ptep = alloc_p2m_pmd(addr, pte_pg);
 		if (!ptep)
 			return false;
 	}

 	if (p2m_top_mfn) {
 		top_mfn_p = &p2m_top_mfn[topidx];
 		mid_mfn = ACCESS_ONCE(p2m_top_mfn_p[topidx]);

 		BUG_ON(virt_to_mfn(mid_mfn) != *top_mfn_p);

 		if (mid_mfn == p2m_mid_missing_mfn) {
 			/* Separately check the mid mfn level */
 			unsigned long missing_mfn;
 			unsigned long mid_mfn_mfn;
 			unsigned long old_mfn;

 			mid_mfn = alloc_p2m_page();
 			if (!mid_mfn)
 				return false;

 			p2m_mid_mfn_init(mid_mfn, p2m_missing);

 			missing_mfn = virt_to_mfn(p2m_mid_missing_mfn);
 			mid_mfn_mfn = virt_to_mfn(mid_mfn);
 			old_mfn = cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn);
 			if (old_mfn != missing_mfn) {
 				free_p2m_page(mid_mfn);
 				mid_mfn = mfn_to_virt(old_mfn);
 			} else {
 				p2m_top_mfn_p[topidx] = mid_mfn;
 			}
 		}
 	} else {
 		mid_mfn = NULL;
 	}

 	p2m_pfn = pte_pfn(READ_ONCE(*ptep));
 	if (p2m_pfn == PFN_DOWN(__pa(p2m_identity)) ||
 	    p2m_pfn == PFN_DOWN(__pa(p2m_missing))) {
 		/* p2m leaf page is missing */
 		unsigned long *p2m;

 		p2m = alloc_p2m_page();
 		if (!p2m)
 			return false;

 		if (p2m_pfn == PFN_DOWN(__pa(p2m_missing)))
 			p2m_init(p2m);
 		else
 			p2m_init_identity(p2m, pfn);

 		spin_lock_irqsave(&p2m_update_lock, flags);

 		if (pte_pfn(*ptep) == p2m_pfn) {
 			set_pte(ptep,
 				pfn_pte(PFN_DOWN(__pa(p2m)), PAGE_KERNEL));
 			if (mid_mfn)
 				mid_mfn[mididx] = virt_to_mfn(p2m);
 			p2m = NULL;
 		}

 		spin_unlock_irqrestore(&p2m_update_lock, flags);

 		if (p2m)
 			free_p2m_page(p2m);
 	}

 	return true;
 }

 unsigned long __init set_phys_range_identity(unsigned long pfn_s,
 				      unsigned long pfn_e)
 {
 	unsigned long pfn;

 	if (unlikely(pfn_s >= xen_p2m_size))
 		return 0;

 	if (unlikely(xen_feature(XENFEAT_auto_translated_physmap)))
 		return pfn_e - pfn_s;

 	if (pfn_s > pfn_e)
 		return 0;

 	if (pfn_e > xen_p2m_size)
 		pfn_e = xen_p2m_size;

 	for (pfn = pfn_s; pfn < pfn_e; pfn++)
 		xen_p2m_addr[pfn] = IDENTITY_FRAME(pfn);

 	return pfn - pfn_s;
 }

 bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 {
 	pte_t *ptep;
 	unsigned int level;

 	/* don't track P2M changes in autotranslate guests */
 	if (unlikely(xen_feature(XENFEAT_auto_translated_physmap)))
 		return true;

 	if (unlikely(pfn >= xen_p2m_size)) {
 		BUG_ON(mfn != INVALID_P2M_ENTRY);
 		return true;
 	}

 	if (likely(!xen_safe_write_ulong(xen_p2m_addr + pfn, mfn)))
 		return true;

 	ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn), &level);
 	BUG_ON(!ptep || level != PG_LEVEL_4K);

 	if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_missing)))
 		return mfn == INVALID_P2M_ENTRY;

 	if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_identity)))
 		return mfn == IDENTITY_FRAME(pfn);

 	return false;
 }

 bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 {
 	if (unlikely(!__set_phys_to_machine(pfn, mfn))) {
 		if (!alloc_p2m(pfn))
 			return false;

 		return __set_phys_to_machine(pfn, mfn);
 	}

 	return true;
 }

 int set_foreign_p2m_mapping(struct gnttab_map_grant_ref *map_ops,
 			    struct gnttab_map_grant_ref *kmap_ops,
 			    struct page **pages, unsigned int count)
 {
 	int i, ret = 0;
 	pte_t *pte;

 	if (xen_feature(XENFEAT_auto_translated_physmap))
 		return 0;

 	if (kmap_ops) {
 		ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
 						kmap_ops, count);
 		if (ret)
 			goto out;
 	}

 	for (i = 0; i < count; i++) {
 		unsigned long mfn, pfn;

 		/* Do not add to override if the map failed. */
 		if (map_ops[i].status)
 			continue;

 		if (map_ops[i].flags & GNTMAP_contains_pte) {
 			pte = (pte_t *)(mfn_to_virt(PFN_DOWN(map_ops[i].host_addr)) +
 				(map_ops[i].host_addr & ~PAGE_MASK));
 			mfn = pte_mfn(*pte);
 		} else {
 			mfn = PFN_DOWN(map_ops[i].dev_bus_addr);
 		}
 		pfn = page_to_pfn(pages[i]);

 		WARN(pfn_to_mfn(pfn) != INVALID_P2M_ENTRY, "page must be ballooned");

 		if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn)))) {
 			ret = -ENOMEM;
 			goto out;
 		}
 	}

 out:
 	return ret;
 }
 EXPORT_SYMBOL_GPL(set_foreign_p2m_mapping);

 int clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref *unmap_ops,
 			      struct gnttab_unmap_grant_ref *kunmap_ops,
 			      struct page **pages, unsigned int count)
 {
 	int i, ret = 0;

 	if (xen_feature(XENFEAT_auto_translated_physmap))
 		return 0;

 	for (i = 0; i < count; i++) {
 		unsigned long mfn = __pfn_to_mfn(page_to_pfn(pages[i]));
 		unsigned long pfn = page_to_pfn(pages[i]);

 		if (mfn == INVALID_P2M_ENTRY || !(mfn & FOREIGN_FRAME_BIT)) {
 			ret = -EINVAL;
 			goto out;
 		}

 		set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 	}
 	if (kunmap_ops)
 		ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
 						kunmap_ops, count);
 out:
 	return ret;
 }
 EXPORT_SYMBOL_GPL(clear_foreign_p2m_mapping);

 #ifdef CONFIG_XEN_DEBUG_FS
 #include <linux/debugfs.h>
 #include "debugfs.h"
 static int p2m_dump_show(struct seq_file *m, void *v)
 {
 	static const char * const type_name[] = {
 				[P2M_TYPE_IDENTITY] = "identity",
 				[P2M_TYPE_MISSING] = "missing",
 				[P2M_TYPE_PFN] = "pfn",
 				[P2M_TYPE_UNKNOWN] = "abnormal"};
 	unsigned long pfn, first_pfn;
 	int type, prev_type;

 	prev_type = xen_p2m_elem_type(0);
 	first_pfn = 0;

 	for (pfn = 0; pfn < xen_p2m_size; pfn++) {
 		type = xen_p2m_elem_type(pfn);
 		if (type != prev_type) {
 			seq_printf(m, " [0x%lx->0x%lx] %s\n", first_pfn, pfn,
 				   type_name[prev_type]);
 			prev_type = type;
 			first_pfn = pfn;
 		}
 	}
 	seq_printf(m, " [0x%lx->0x%lx] %s\n", first_pfn, pfn,
 		   type_name[prev_type]);
 	return 0;
 }

 static int p2m_dump_open(struct inode *inode, struct file *filp)
 {
 	return single_open(filp, p2m_dump_show, NULL);
 }

 static const struct file_operations p2m_dump_fops = {
 	.open		= p2m_dump_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
 	.release	= single_release,
 };

 static struct dentry *d_mmu_debug;

 static int __init xen_p2m_debugfs(void)
 {
 	struct dentry *d_xen = xen_init_debugfs();

 	if (d_xen == NULL)
 		return -ENOMEM;

 	d_mmu_debug = debugfs_create_dir("mmu", d_xen);

 	debugfs_create_file("p2m", 0600, d_mmu_debug, NULL, &p2m_dump_fops);
 	return 0;
 }
 fs_initcall(xen_p2m_debugfs);
 #endif /* CONFIG_XEN_DEBUG_FS */
	/*
	* Xen leaves the responsibility for maintaining p2m mappings to the
	* guests themselves, but it must also access and update the p2m array
	* during suspend/resume when all the pages are reallocated.
	*
	* The logical flat p2m table is mapped to a linear kernel memory area.
	* For accesses by Xen a three-level tree linked via mfns only is set up to
	* allow the address space to be sparse.
	*
	* Xen
	* \|
	* p2m_top_mfn
	* / \
	* p2m_mid_mfn p2m_mid_mfn
	* / /
	* p2m p2m p2m ...
	*
	* The p2m_mid_mfn pages are mapped by p2m_top_mfn_p.
	*
	* The p2m_top_mfn level is limited to 1 page, so the maximum representable
	* pseudo-physical address space is:
	* P2M_TOP_PER_PAGE * P2M_MID_PER_PAGE * P2M_PER_PAGE pages
	*
	* P2M_PER_PAGE depends on the architecture, as a mfn is always
	* unsigned long (8 bytes on 64-bit, 4 bytes on 32), leading to
	* 512 and 1024 entries respectively.
	*
	* In short, these structures contain the Machine Frame Number (MFN) of the PFN.
	*
	* However not all entries are filled with MFNs. Specifically for all other
	* leaf entries, or for the top root, or middle one, for which there is a void
	* entry, we assume it is "missing". So (for example)
	* pfn_to_mfn(0x90909090)=INVALID_P2M_ENTRY.
	* We have a dedicated page p2m_missing with all entries being
	* INVALID_P2M_ENTRY. This page may be referenced multiple times in the p2m
	* list/tree in case there are multiple areas with P2M_PER_PAGE invalid pfns.
	*
	* We also have the possibility of setting 1-1 mappings on certain regions, so
	* that:
	* pfn_to_mfn(0xc0000)=0xc0000
	*
	* The benefit of this is, that we can assume for non-RAM regions (think
	* PCI BARs, or ACPI spaces), we can create mappings easily because we
	* get the PFN value to match the MFN.
	*
	* For this to work efficiently we have one new page p2m_identity. All entries
	* in p2m_identity are set to INVALID_P2M_ENTRY type (Xen toolstack only
	* recognizes that and MFNs, no other fancy value).
	*
	* On lookup we spot that the entry points to p2m_identity and return the
	* identity value instead of dereferencing and returning INVALID_P2M_ENTRY.
	* If the entry points to an allocated page, we just proceed as before and
	* return the PFN. If the PFN has IDENTITY_FRAME_BIT set we unmask that in
	* appropriate functions (pfn_to_mfn).
	*
	* The reason for having the IDENTITY_FRAME_BIT instead of just returning the
	* PFN is that we could find ourselves where pfn_to_mfn(pfn)==pfn for a
	* non-identity pfn. To protect ourselves against we elect to set (and get) the
	* IDENTITY_FRAME_BIT on all identity mapped PFNs.
	*/

	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/list.h>
	#include <linux/hash.h>
	#include <linux/sched.h>
	#include <linux/seq_file.h>
	#include <linux/bootmem.h>
	#include <linux/slab.h>

	#include <asm/cache.h>
	#include <asm/setup.h>
	#include <asm/uaccess.h>

	#include <asm/xen/page.h>
	#include <asm/xen/hypercall.h>
	#include <asm/xen/hypervisor.h>
	#include <xen/balloon.h>
	#include <xen/grant_table.h>

	#include "p2m.h"
	#include "multicalls.h"
	#include "xen-ops.h"

	#define PMDS_PER_MID_PAGE (P2M_MID_PER_PAGE / PTRS_PER_PTE)

	unsigned long *xen_p2m_addr __read_mostly;
	EXPORT_SYMBOL_GPL(xen_p2m_addr);
	unsigned long xen_p2m_size __read_mostly;
	EXPORT_SYMBOL_GPL(xen_p2m_size);
	unsigned long xen_max_p2m_pfn __read_mostly;
	EXPORT_SYMBOL_GPL(xen_max_p2m_pfn);

	static DEFINE_SPINLOCK(p2m_update_lock);

	static unsigned long *p2m_mid_missing_mfn;
	static unsigned long *p2m_top_mfn;
	static unsigned long **p2m_top_mfn_p;
	static unsigned long *p2m_missing;
	static unsigned long *p2m_identity;
	static pte_t *p2m_missing_pte;
	static pte_t *p2m_identity_pte;

	static inline unsigned p2m_top_index(unsigned long pfn)
	{
	BUG_ON(pfn >= MAX_P2M_PFN);
	return pfn / (P2M_MID_PER_PAGE * P2M_PER_PAGE);
	}

	static inline unsigned p2m_mid_index(unsigned long pfn)
	{
	return (pfn / P2M_PER_PAGE) % P2M_MID_PER_PAGE;
	}

	static inline unsigned p2m_index(unsigned long pfn)
	{
	return pfn % P2M_PER_PAGE;
	}

	static void p2m_top_mfn_init(unsigned long *top)
	{
	unsigned i;

	for (i = 0; i < P2M_TOP_PER_PAGE; i++)
	top[i] = virt_to_mfn(p2m_mid_missing_mfn);
	}

	static void p2m_top_mfn_p_init(unsigned long **top)
	{
	unsigned i;

	for (i = 0; i < P2M_TOP_PER_PAGE; i++)
	top[i] = p2m_mid_missing_mfn;
	}

	static void p2m_mid_mfn_init(unsigned long mid, unsigned long leaf)
	{
	unsigned i;

	for (i = 0; i < P2M_MID_PER_PAGE; i++)
	mid[i] = virt_to_mfn(leaf);
	}

	static void p2m_init(unsigned long *p2m)
	{
	unsigned i;

	for (i = 0; i < P2M_PER_PAGE; i++)
	p2m[i] = INVALID_P2M_ENTRY;
	}

	static void p2m_init_identity(unsigned long *p2m, unsigned long pfn)
	{
	unsigned i;

	for (i = 0; i < P2M_PER_PAGE; i++)
	p2m[i] = IDENTITY_FRAME(pfn + i);
	}

	static void * __ref alloc_p2m_page(void)
	{
	if (unlikely(!slab_is_available()))
	return alloc_bootmem_align(PAGE_SIZE, PAGE_SIZE);

	return (void *)__get_free_page(GFP_KERNEL \| __GFP_REPEAT);
	}

	static void __ref free_p2m_page(void *p)
	{
	if (unlikely(!slab_is_available())) {
	free_bootmem((unsigned long)p, PAGE_SIZE);
	return;
	}

	free_page((unsigned long)p);
	}

	/*
	* Build the parallel p2m_top_mfn and p2m_mid_mfn structures
	*
	* This is called both at boot time, and after resuming from suspend:
	* - At boot time we're called rather early, and must use alloc_bootmem*()
	* to allocate memory.
	*
	* - After resume we're called from within stop_machine, but the mfn
	* tree should already be completely allocated.
	*/
	void __ref xen_build_mfn_list_list(void)
	{
	unsigned long pfn, mfn;
	pte_t *ptep;
	unsigned int level, topidx, mididx;
	unsigned long *mid_mfn_p;

	if (xen_feature(XENFEAT_auto_translated_physmap))
	return;

	/* Pre-initialize p2m_top_mfn to be completely missing */
	if (p2m_top_mfn == NULL) {
	p2m_mid_missing_mfn = alloc_p2m_page();
	p2m_mid_mfn_init(p2m_mid_missing_mfn, p2m_missing);

	p2m_top_mfn_p = alloc_p2m_page();
	p2m_top_mfn_p_init(p2m_top_mfn_p);

	p2m_top_mfn = alloc_p2m_page();
	p2m_top_mfn_init(p2m_top_mfn);
	} else {
	/* Reinitialise, mfn's all change after migration */
	p2m_mid_mfn_init(p2m_mid_missing_mfn, p2m_missing);
	}

	for (pfn = 0; pfn < xen_max_p2m_pfn && pfn < MAX_P2M_PFN;
	pfn += P2M_PER_PAGE) {
	topidx = p2m_top_index(pfn);
	mididx = p2m_mid_index(pfn);

	mid_mfn_p = p2m_top_mfn_p[topidx];
	ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn),
	&level);
	BUG_ON(!ptep \|\| level != PG_LEVEL_4K);
	mfn = pte_mfn(*ptep);
	ptep = (pte_t *)((unsigned long)ptep & ~(PAGE_SIZE - 1));

	/* Don't bother allocating any mfn mid levels if
	* they're just missing, just update the stored mfn,
	* since all could have changed over a migrate.
	*/
	if (ptep == p2m_missing_pte \|\| ptep == p2m_identity_pte) {
	BUG_ON(mididx);
	BUG_ON(mid_mfn_p != p2m_mid_missing_mfn);
	p2m_top_mfn[topidx] = virt_to_mfn(p2m_mid_missing_mfn);
	pfn += (P2M_MID_PER_PAGE - 1) * P2M_PER_PAGE;
	continue;
	}

	if (mid_mfn_p == p2m_mid_missing_mfn) {
	mid_mfn_p = alloc_p2m_page();
	p2m_mid_mfn_init(mid_mfn_p, p2m_missing);

	p2m_top_mfn_p[topidx] = mid_mfn_p;
	}

	p2m_top_mfn[topidx] = virt_to_mfn(mid_mfn_p);
	mid_mfn_p[mididx] = mfn;
	}
	}

	void xen_setup_mfn_list_list(void)
	{
	if (xen_feature(XENFEAT_auto_translated_physmap))
	return;

	BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);

	HYPERVISOR_shared_info->arch.pfn_to_mfn_frame_list_list =
	virt_to_mfn(p2m_top_mfn);
	HYPERVISOR_shared_info->arch.max_pfn = xen_max_p2m_pfn;
	}

	/* Set up p2m_top to point to the domain-builder provided p2m pages */
	void __init xen_build_dynamic_phys_to_machine(void)
	{
	unsigned long pfn;

	if (xen_feature(XENFEAT_auto_translated_physmap))
	return;

	xen_p2m_addr = (unsigned long *)xen_start_info->mfn_list;
	xen_p2m_size = ALIGN(xen_start_info->nr_pages, P2M_PER_PAGE);

	for (pfn = xen_start_info->nr_pages; pfn < xen_p2m_size; pfn++)
	xen_p2m_addr[pfn] = INVALID_P2M_ENTRY;

	xen_max_p2m_pfn = xen_p2m_size;
	}

	#define P2M_TYPE_IDENTITY 0
	#define P2M_TYPE_MISSING 1
	#define P2M_TYPE_PFN 2
	#define P2M_TYPE_UNKNOWN 3

	static int xen_p2m_elem_type(unsigned long pfn)
	{
	unsigned long mfn;

	if (pfn >= xen_p2m_size)
	return P2M_TYPE_IDENTITY;

	mfn = xen_p2m_addr[pfn];

	if (mfn == INVALID_P2M_ENTRY)
	return P2M_TYPE_MISSING;

	if (mfn & IDENTITY_FRAME_BIT)
	return P2M_TYPE_IDENTITY;

	return P2M_TYPE_PFN;
	}

	static void __init xen_rebuild_p2m_list(unsigned long *p2m)
	{
	unsigned int i, chunk;
	unsigned long pfn;
	unsigned long *mfns;
	pte_t *ptep;
	pmd_t *pmdp;
	int type;

	p2m_missing = alloc_p2m_page();
	p2m_init(p2m_missing);
	p2m_identity = alloc_p2m_page();
	p2m_init(p2m_identity);

	p2m_missing_pte = alloc_p2m_page();
	paravirt_alloc_pte(&init_mm, __pa(p2m_missing_pte) >> PAGE_SHIFT);
	p2m_identity_pte = alloc_p2m_page();
	paravirt_alloc_pte(&init_mm, __pa(p2m_identity_pte) >> PAGE_SHIFT);
	for (i = 0; i < PTRS_PER_PTE; i++) {
	set_pte(p2m_missing_pte + i,
	pfn_pte(PFN_DOWN(__pa(p2m_missing)), PAGE_KERNEL_RO));
	set_pte(p2m_identity_pte + i,
	pfn_pte(PFN_DOWN(__pa(p2m_identity)), PAGE_KERNEL_RO));
	}

	for (pfn = 0; pfn < xen_max_p2m_pfn; pfn += chunk) {
	/*
	* Try to map missing/identity PMDs or p2m-pages if possible.
	* We have to respect the structure of the mfn_list_list
	* which will be built just afterwards.
	* Chunk size to test is one p2m page if we are in the middle
	* of a mfn_list_list mid page and the complete mid page area
	* if we are at index 0 of the mid page. Please note that a
	* mid page might cover more than one PMD, e.g. on 32 bit PAE
	* kernels.
	*/
	chunk = (pfn & (P2M_PER_PAGE * P2M_MID_PER_PAGE - 1)) ?
	P2M_PER_PAGE : P2M_PER_PAGE * P2M_MID_PER_PAGE;

	type = xen_p2m_elem_type(pfn);
	i = 0;
	if (type != P2M_TYPE_PFN)
	for (i = 1; i < chunk; i++)
	if (xen_p2m_elem_type(pfn + i) != type)
	break;
	if (i < chunk)
	/* Reset to minimal chunk size. */
	chunk = P2M_PER_PAGE;

	if (type == P2M_TYPE_PFN \|\| i < chunk) {
	/* Use initial p2m page contents. */
	#ifdef CONFIG_X86_64
	mfns = alloc_p2m_page();
	copy_page(mfns, xen_p2m_addr + pfn);
	#else
	mfns = xen_p2m_addr + pfn;
	#endif
	ptep = populate_extra_pte((unsigned long)(p2m + pfn));
	set_pte(ptep,
	pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL));
	continue;
	}

	if (chunk == P2M_PER_PAGE) {
	/* Map complete missing or identity p2m-page. */
	mfns = (type == P2M_TYPE_MISSING) ?
	p2m_missing : p2m_identity;
	ptep = populate_extra_pte((unsigned long)(p2m + pfn));
	set_pte(ptep,
	pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL_RO));
	continue;
	}

	/* Complete missing or identity PMD(s) can be mapped. */
	ptep = (type == P2M_TYPE_MISSING) ?
	p2m_missing_pte : p2m_identity_pte;
	for (i = 0; i < PMDS_PER_MID_PAGE; i++) {
	pmdp = populate_extra_pmd(
	(unsigned long)(p2m + pfn) + i * PMD_SIZE);
	set_pmd(pmdp, __pmd(__pa(ptep) \| _KERNPG_TABLE));
	}
	}
	}

	void __init xen_vmalloc_p2m_tree(void)
	{
	static struct vm_struct vm;

	vm.flags = VM_ALLOC;
	vm.size = ALIGN(sizeof(unsigned long) * xen_max_p2m_pfn,
	PMD_SIZE * PMDS_PER_MID_PAGE);
	vm_area_register_early(&vm, PMD_SIZE * PMDS_PER_MID_PAGE);
	pr_notice("p2m virtual area at %p, size is %lx\n", vm.addr, vm.size);

	xen_max_p2m_pfn = vm.size / sizeof(unsigned long);

	xen_rebuild_p2m_list(vm.addr);

	xen_p2m_addr = vm.addr;
	xen_p2m_size = xen_max_p2m_pfn;

	xen_inv_extra_mem();
	}

	unsigned long get_phys_to_machine(unsigned long pfn)
	{
	pte_t *ptep;
	unsigned int level;

	if (unlikely(pfn >= xen_p2m_size)) {
	if (pfn < xen_max_p2m_pfn)
	return xen_chk_extra_mem(pfn);

	return IDENTITY_FRAME(pfn);
	}

	ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn), &level);
	BUG_ON(!ptep \|\| level != PG_LEVEL_4K);

	/*
	* The INVALID_P2M_ENTRY is filled in both p2m_*identity
	* and in p2m_*missing, so returning the INVALID_P2M_ENTRY
	* would be wrong.
	*/
	if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_identity)))
	return IDENTITY_FRAME(pfn);

	return xen_p2m_addr[pfn];
	}
	EXPORT_SYMBOL_GPL(get_phys_to_machine);

	/*
	* Allocate new pmd(s). It is checked whether the old pmd is still in place.
	* If not, nothing is changed. This is okay as the only reason for allocating
	* a new pmd is to replace p2m_missing_pte or p2m_identity_pte by a individual
	* pmd. In case of PAE/x86-32 there are multiple pmds to allocate!
	*/
	static pte_t alloc_p2m_pmd(unsigned long addr, pte_t pte_pg)
	{
	pte_t *ptechk;
	pte_t *pte_newpg[PMDS_PER_MID_PAGE];
	pmd_t *pmdp;
	unsigned int level;
	unsigned long flags;
	unsigned long vaddr;
	int i;

	/* Do all allocations first to bail out in error case. */
	for (i = 0; i < PMDS_PER_MID_PAGE; i++) {
	pte_newpg[i] = alloc_p2m_page();
	if (!pte_newpg[i]) {
	for (i--; i >= 0; i--)
	free_p2m_page(pte_newpg[i]);

	return NULL;
	}
	}

	vaddr = addr & ~(PMD_SIZE * PMDS_PER_MID_PAGE - 1);

	for (i = 0; i < PMDS_PER_MID_PAGE; i++) {
	copy_page(pte_newpg[i], pte_pg);
	paravirt_alloc_pte(&init_mm, __pa(pte_newpg[i]) >> PAGE_SHIFT);

	pmdp = lookup_pmd_address(vaddr);
	BUG_ON(!pmdp);

	spin_lock_irqsave(&p2m_update_lock, flags);

	ptechk = lookup_address(vaddr, &level);
	if (ptechk == pte_pg) {
	set_pmd(pmdp,
	__pmd(__pa(pte_newpg[i]) \| _KERNPG_TABLE));
	pte_newpg[i] = NULL;
	}

	spin_unlock_irqrestore(&p2m_update_lock, flags);

	if (pte_newpg[i]) {
	paravirt_release_pte(__pa(pte_newpg[i]) >> PAGE_SHIFT);
	free_p2m_page(pte_newpg[i]);
	}

	vaddr += PMD_SIZE;
	}

	return lookup_address(addr, &level);
	}

	/*
	* Fully allocate the p2m structure for a given pfn. We need to check
	* that both the top and mid levels are allocated, and make sure the
	* parallel mfn tree is kept in sync. We may race with other cpus, so
	* the new pages are installed with cmpxchg; if we lose the race then
	* simply free the page we allocated and use the one that's there.
	*/
	static bool alloc_p2m(unsigned long pfn)
	{
	unsigned topidx, mididx;
	unsigned long top_mfn_p, mid_mfn;
	pte_t ptep, pte_pg;
	unsigned int level;
	unsigned long flags;
	unsigned long addr = (unsigned long)(xen_p2m_addr + pfn);
	unsigned long p2m_pfn;

	topidx = p2m_top_index(pfn);
	mididx = p2m_mid_index(pfn);

	ptep = lookup_address(addr, &level);
	BUG_ON(!ptep \|\| level != PG_LEVEL_4K);
	pte_pg = (pte_t *)((unsigned long)ptep & ~(PAGE_SIZE - 1));

	if (pte_pg == p2m_missing_pte \|\| pte_pg == p2m_identity_pte) {
	/* PMD level is missing, allocate a new one */
	ptep = alloc_p2m_pmd(addr, pte_pg);
	if (!ptep)
	return false;
	}

	if (p2m_top_mfn) {
	top_mfn_p = &p2m_top_mfn[topidx];
	mid_mfn = ACCESS_ONCE(p2m_top_mfn_p[topidx]);

	BUG_ON(virt_to_mfn(mid_mfn) != *top_mfn_p);

	if (mid_mfn == p2m_mid_missing_mfn) {
	/* Separately check the mid mfn level */
	unsigned long missing_mfn;
	unsigned long mid_mfn_mfn;
	unsigned long old_mfn;

	mid_mfn = alloc_p2m_page();
	if (!mid_mfn)
	return false;

	p2m_mid_mfn_init(mid_mfn, p2m_missing);

	missing_mfn = virt_to_mfn(p2m_mid_missing_mfn);
	mid_mfn_mfn = virt_to_mfn(mid_mfn);
	old_mfn = cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn);
	if (old_mfn != missing_mfn) {
	free_p2m_page(mid_mfn);
	mid_mfn = mfn_to_virt(old_mfn);
	} else {
	p2m_top_mfn_p[topidx] = mid_mfn;
	}
	}
	} else {
	mid_mfn = NULL;
	}

	p2m_pfn = pte_pfn(READ_ONCE(*ptep));
	if (p2m_pfn == PFN_DOWN(__pa(p2m_identity)) \|\|
	p2m_pfn == PFN_DOWN(__pa(p2m_missing))) {
	/* p2m leaf page is missing */
	unsigned long *p2m;

	p2m = alloc_p2m_page();
	if (!p2m)
	return false;

	if (p2m_pfn == PFN_DOWN(__pa(p2m_missing)))
	p2m_init(p2m);
	else
	p2m_init_identity(p2m, pfn);

	spin_lock_irqsave(&p2m_update_lock, flags);

	if (pte_pfn(*ptep) == p2m_pfn) {
	set_pte(ptep,
	pfn_pte(PFN_DOWN(__pa(p2m)), PAGE_KERNEL));
	if (mid_mfn)
	mid_mfn[mididx] = virt_to_mfn(p2m);
	p2m = NULL;
	}

	spin_unlock_irqrestore(&p2m_update_lock, flags);

	if (p2m)
	free_p2m_page(p2m);
	}

	return true;
	}

	unsigned long __init set_phys_range_identity(unsigned long pfn_s,
	unsigned long pfn_e)
	{
	unsigned long pfn;

	if (unlikely(pfn_s >= xen_p2m_size))
	return 0;

	if (unlikely(xen_feature(XENFEAT_auto_translated_physmap)))
	return pfn_e - pfn_s;

	if (pfn_s > pfn_e)
	return 0;

	if (pfn_e > xen_p2m_size)
	pfn_e = xen_p2m_size;

	for (pfn = pfn_s; pfn < pfn_e; pfn++)
	xen_p2m_addr[pfn] = IDENTITY_FRAME(pfn);

	return pfn - pfn_s;
	}

	bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
	{
	pte_t *ptep;
	unsigned int level;

	/* don't track P2M changes in autotranslate guests */
	if (unlikely(xen_feature(XENFEAT_auto_translated_physmap)))
	return true;

	if (unlikely(pfn >= xen_p2m_size)) {
	BUG_ON(mfn != INVALID_P2M_ENTRY);
	return true;
	}

	if (likely(!xen_safe_write_ulong(xen_p2m_addr + pfn, mfn)))
	return true;

	ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn), &level);
	BUG_ON(!ptep \|\| level != PG_LEVEL_4K);

	if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_missing)))
	return mfn == INVALID_P2M_ENTRY;

	if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_identity)))
	return mfn == IDENTITY_FRAME(pfn);

	return false;
	}

	bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)
	{
	if (unlikely(!__set_phys_to_machine(pfn, mfn))) {
	if (!alloc_p2m(pfn))
	return false;

	return __set_phys_to_machine(pfn, mfn);
	}

	return true;
	}

	int set_foreign_p2m_mapping(struct gnttab_map_grant_ref *map_ops,
	struct gnttab_map_grant_ref *kmap_ops,
	struct page **pages, unsigned int count)
	{
	int i, ret = 0;
	pte_t *pte;

	if (xen_feature(XENFEAT_auto_translated_physmap))
	return 0;

	if (kmap_ops) {
	ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
	kmap_ops, count);
	if (ret)
	goto out;
	}

	for (i = 0; i < count; i++) {
	unsigned long mfn, pfn;

	/* Do not add to override if the map failed. */
	if (map_ops[i].status)
	continue;

	if (map_ops[i].flags & GNTMAP_contains_pte) {
	pte = (pte_t *)(mfn_to_virt(PFN_DOWN(map_ops[i].host_addr)) +
	(map_ops[i].host_addr & ~PAGE_MASK));
	mfn = pte_mfn(*pte);
	} else {
	mfn = PFN_DOWN(map_ops[i].dev_bus_addr);
	}
	pfn = page_to_pfn(pages[i]);

	WARN(pfn_to_mfn(pfn) != INVALID_P2M_ENTRY, "page must be ballooned");

	if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn)))) {
	ret = -ENOMEM;
	goto out;
	}
	}

	out:
	return ret;
	}
	EXPORT_SYMBOL_GPL(set_foreign_p2m_mapping);

	int clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref *unmap_ops,
	struct gnttab_unmap_grant_ref *kunmap_ops,
	struct page **pages, unsigned int count)
	{
	int i, ret = 0;

	if (xen_feature(XENFEAT_auto_translated_physmap))
	return 0;

	for (i = 0; i < count; i++) {
	unsigned long mfn = __pfn_to_mfn(page_to_pfn(pages[i]));
	unsigned long pfn = page_to_pfn(pages[i]);

	if (mfn == INVALID_P2M_ENTRY \|\| !(mfn & FOREIGN_FRAME_BIT)) {
	ret = -EINVAL;
	goto out;
	}

	set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
	}
	if (kunmap_ops)
	ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
	kunmap_ops, count);
	out:
	return ret;
	}
	EXPORT_SYMBOL_GPL(clear_foreign_p2m_mapping);

	#ifdef CONFIG_XEN_DEBUG_FS
	#include <linux/debugfs.h>
	#include "debugfs.h"
	static int p2m_dump_show(struct seq_file m, void v)
	{
	static const char * const type_name[] = {
	[P2M_TYPE_IDENTITY] = "identity",
	[P2M_TYPE_MISSING] = "missing",
	[P2M_TYPE_PFN] = "pfn",
	[P2M_TYPE_UNKNOWN] = "abnormal"};
	unsigned long pfn, first_pfn;
	int type, prev_type;

	prev_type = xen_p2m_elem_type(0);
	first_pfn = 0;

	for (pfn = 0; pfn < xen_p2m_size; pfn++) {
	type = xen_p2m_elem_type(pfn);
	if (type != prev_type) {
	seq_printf(m, " [0x%lx->0x%lx] %s\n", first_pfn, pfn,
	type_name[prev_type]);
	prev_type = type;
	first_pfn = pfn;
	}
	}
	seq_printf(m, " [0x%lx->0x%lx] %s\n", first_pfn, pfn,
	type_name[prev_type]);
	return 0;
	}

	static int p2m_dump_open(struct inode inode, struct file filp)
	{
	return single_open(filp, p2m_dump_show, NULL);
	}

	static const struct file_operations p2m_dump_fops = {
	.open = p2m_dump_open,
	.read = seq_read,
	.llseek = seq_lseek,
	.release = single_release,
	};

	static struct dentry *d_mmu_debug;

	static int __init xen_p2m_debugfs(void)
	{
	struct dentry *d_xen = xen_init_debugfs();

	if (d_xen == NULL)
	return -ENOMEM;

	d_mmu_debug = debugfs_create_dir("mmu", d_xen);

	debugfs_create_file("p2m", 0600, d_mmu_debug, NULL, &p2m_dump_fops);
	return 0;
	}
	fs_initcall(xen_p2m_debugfs);
	#endif /* CONFIG_XEN_DEBUG_FS */