/*
   * 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 p2m table is logically a flat array, but we implement it as a
   * three-level tree to allow the address space to be sparse.
   *
   *                               Xen
   *                                |
   *     p2m_top              p2m_top_mfn
   *       /  \                   /   \
   * p2m_mid p2m_mid	p2m_mid_mfn p2m_mid_mfn
   *    / \      / \         /           /
   *  p2m p2m p2m p2m p2m p2m p2m ...
   *
   * The p2m_mid_mfn pages are mapped by p2m_top_mfn_p.
   *
   * The p2m_top and p2m_top_mfn levels are 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 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 b/c we
   * get the PFN value to match the MFN.
   *
   * For this to work efficiently we have one new page p2m_identity and
   * allocate (via reserved_brk) any other pages we need to cover the sides
   * (1GB or 4MB boundary violations). 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.
   *
   * This simplistic diagram is used to explain the more subtle piece of code.
   * There is also a digram of the P2M at the end that can help.
   * Imagine your E820 looking as so:
   *
   *                    1GB                                           2GB
   * /-------------------+---------\/----\         /----------\    /---+-----\
   * | System RAM        | Sys RAM ||ACPI|         | reserved |    | Sys RAM |
   * \-------------------+---------/\----/         \----------/    \---+-----/
   *                               ^- 1029MB                       ^- 2001MB
   *
   * [1029MB = 263424 (0x40500), 2001MB = 512256 (0x7D100),
   *  2048MB = 524288 (0x80000)]
   *
   * And dom0_mem=max:3GB,1GB is passed in to the guest, meaning memory past 1GB
   * is actually not present (would have to kick the balloon driver to put it in).
   *
   * When we are told to set the PFNs for identity mapping (see patch: "xen/setup:
   * Set identity mapping for non-RAM E820 and E820 gaps.") we pass in the start
   * of the PFN and the end PFN (263424 and 512256 respectively). The first step
   * is to reserve_brk a top leaf page if the p2m[1] is missing. The top leaf page
   * covers 512^2 of page estate (1GB) and in case the start or end PFN is not
   * aligned on 512^2*PAGE_SIZE (1GB) we loop on aligned 1GB PFNs from start pfn
   * to end pfn.  We reserve_brk top leaf pages if they are missing (means they
   * point to p2m_mid_missing).
   *
   * With the E820 example above, 263424 is not 1GB aligned so we allocate a
   * reserve_brk page which will cover the PFNs estate from 0x40000 to 0x80000.
   * Each entry in the allocate page is "missing" (points to p2m_missing).
   *
   * Next stage is to determine if we need to do a more granular boundary check
   * on the 4MB (or 2MB depending on architecture) off the start and end pfn's.
   * We check if the start pfn and end pfn violate that boundary check, and if
   * so reserve_brk a middle (p2m[x][y]) leaf page. This way we have a much finer
   * granularity of setting which PFNs are missing and which ones are identity.
   * In our example 263424 and 512256 both fail the check so we reserve_brk two
   * pages. Populate them with INVALID_P2M_ENTRY (so they both have "missing"
   * values) and assign them to p2m[1][2] and p2m[1][488] respectively.
   *
   * At this point we would at minimum reserve_brk one page, but could be up to
   * three. Each call to set_phys_range_identity has at maximum a three page
   * cost. If we were to query the P2M at this stage, all those entries from
   * start PFN through end PFN (so 1029MB -> 2001MB) would return
   * INVALID_P2M_ENTRY ("missing").
   *
   * The next step is to walk from the start pfn to the end pfn setting
   * the IDENTITY_FRAME_BIT on each PFN. This is done in set_phys_range_identity.
   * If we find that the middle leaf is pointing to p2m_missing we can swap it
   * over to p2m_identity - this way covering 4MB (or 2MB) PFN space.  At this
   * point we do not need to worry about boundary aligment (so no need to
   * reserve_brk a middle page, figure out which PFNs are "missing" and which
   * ones are identity), as that has been done earlier.  If we find that the
   * middle leaf is not occupied by p2m_identity or p2m_missing, we dereference
   * that page (which covers 512 PFNs) and set the appropriate PFN with
   * IDENTITY_FRAME_BIT. In our example 263424 and 512256 end up there, and we
   * set from p2m[1][2][256->511] and p2m[1][488][0->256] with
   * IDENTITY_FRAME_BIT set.
   *
   * All other regions that are void (or not filled) either point to p2m_missing
   * (considered missing) or have the default value of INVALID_P2M_ENTRY (also
   * considered missing). In our case, p2m[1][2][0->255] and p2m[1][488][257->511]
   * contain the INVALID_P2M_ENTRY value and are considered "missing."
   *
   * This is what the p2m ends up looking (for the E820 above) with this
   * fabulous drawing:
   *
   *    p2m         /--------------\
   *  /-----\       | &mfn_list[0],|                           /-----------------\
   *  |  0  |------>| &mfn_list[1],|    /---------------\      | ~0, ~0, ..      |
   *  |-----|       |  ..., ~0, ~0 |    | ~0, ~0, [x]---+----->| IDENTITY [@256] |
   *  |  1  |---\   \--------------/    | [p2m_identity]+\     | IDENTITY [@257] |
   *  |-----|    \                      | [p2m_identity]+\\    | ....            |
   *  |  2  |--\  \-------------------->|  ...          | \\   \----------------/
   *  |-----|   \                       \---------------/  \\
   *  |  3  |\   \                                          \\  p2m_identity
   *  |-----| \   \-------------------->/---------------\   /-----------------\
   *  | ..  +->+                        | [p2m_identity]+-->| ~0, ~0, ~0, ... |
   *  \-----/ /                         | [p2m_identity]+-->| ..., ~0         |
   *         / /---------------\        | ....          |   \-----------------/
   *        /  | IDENTITY[@0]  |      /-+-[x], ~0, ~0.. |
   *       /   | IDENTITY[@256]|<----/  \---------------/
   *      /    | ~0, ~0, ....  |
   *     |     \---------------/
   *     |
   *   p2m_mid_missing           p2m_missing
   * /-----------------\     /------------\
   * | [p2m_missing]   +---->| ~0, ~0, ~0 |
   * | [p2m_missing]   +---->| ..., ~0    |
   * \-----------------/     \------------/
   *
   * where ~0 is INVALID_P2M_ENTRY. IDENTITY is (PFN | IDENTITY_BIT)
   */
  
  #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 <asm/cache.h>
  #include <asm/setup.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 "multicalls.h"
  #include "xen-ops.h"
  
  static void __init m2p_override_init(void);
  
  unsigned long xen_max_p2m_pfn __read_mostly;
  
  #define P2M_PER_PAGE		(PAGE_SIZE / sizeof(unsigned long))
  #define P2M_MID_PER_PAGE	(PAGE_SIZE / sizeof(unsigned long *))
  #define P2M_TOP_PER_PAGE	(PAGE_SIZE / sizeof(unsigned long **))
  
  #define MAX_P2M_PFN		(P2M_TOP_PER_PAGE * P2M_MID_PER_PAGE * P2M_PER_PAGE)
  
  /* Placeholders for holes in the address space */
  static RESERVE_BRK_ARRAY(unsigned long, p2m_missing, P2M_PER_PAGE);
  static RESERVE_BRK_ARRAY(unsigned long *, p2m_mid_missing, P2M_MID_PER_PAGE);
  static RESERVE_BRK_ARRAY(unsigned long, p2m_mid_missing_mfn, P2M_MID_PER_PAGE);
  
  static RESERVE_BRK_ARRAY(unsigned long **, p2m_top, P2M_TOP_PER_PAGE);
  static RESERVE_BRK_ARRAY(unsigned long, p2m_top_mfn, P2M_TOP_PER_PAGE);
  static RESERVE_BRK_ARRAY(unsigned long *, p2m_top_mfn_p, P2M_TOP_PER_PAGE);
  
  static RESERVE_BRK_ARRAY(unsigned long, p2m_identity, P2M_PER_PAGE);
  
  RESERVE_BRK(p2m_mid, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID_PER_PAGE)));
  RESERVE_BRK(p2m_mid_mfn, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID_PER_PAGE)));
  
  /* We might hit two boundary violations at the start and end, at max each
   * boundary violation will require three middle nodes. */
  RESERVE_BRK(p2m_mid_identity, PAGE_SIZE * 2 * 3);
  
  /* When we populate back during bootup, the amount of pages can vary. The
   * max we have is seen is 395979, but that does not mean it can't be more.
   * Some machines can have 3GB I/O holes even. With early_can_reuse_p2m_middle
   * it can re-use Xen provided mfn_list array, so we only need to allocate at
   * most three P2M top nodes. */
  RESERVE_BRK(p2m_populated, PAGE_SIZE * 3);
  
  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_init(unsigned long ***top)
  {
  	unsigned i;
  
  	for (i = 0; i < P2M_TOP_PER_PAGE; i++)
  		top[i] = p2m_mid_missing;
  }
  
  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_init(unsigned long **mid)
  {
  	unsigned i;
  
  	for (i = 0; i < P2M_MID_PER_PAGE; i++)
  		mid[i] = p2m_missing;
  }
  
  static void p2m_mid_mfn_init(unsigned long *mid)
  {
  	unsigned i;
  
  	for (i = 0; i < P2M_MID_PER_PAGE; i++)
  		mid[i] = virt_to_mfn(p2m_missing);
  }
  
  static void p2m_init(unsigned long *p2m)
  {
  	unsigned i;
  
  	for (i = 0; i < P2M_MID_PER_PAGE; i++)
  		p2m[i] = INVALID_P2M_ENTRY;
  }
  
  /*
   * 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 very early, and must use extend_brk()
   *   to allocate memory.
   *
   * - After resume we're called from within stop_machine, but the mfn
   *   tree should alreay be completely allocated.
   */
  void __ref xen_build_mfn_list_list(void)
  {
  	unsigned long pfn;
  
  	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 = extend_brk(PAGE_SIZE, PAGE_SIZE);
  		p2m_mid_mfn_init(p2m_mid_missing_mfn);
  
  		p2m_top_mfn_p = extend_brk(PAGE_SIZE, PAGE_SIZE);
  		p2m_top_mfn_p_init(p2m_top_mfn_p);
  
  		p2m_top_mfn = extend_brk(PAGE_SIZE, PAGE_SIZE);
  		p2m_top_mfn_init(p2m_top_mfn);
  	} else {
  		/* Reinitialise, mfn's all change after migration */
  		p2m_mid_mfn_init(p2m_mid_missing_mfn);
  	}
  
  	for (pfn = 0; pfn < xen_max_p2m_pfn; pfn += P2M_PER_PAGE) {
  		unsigned topidx = p2m_top_index(pfn);
  		unsigned mididx = p2m_mid_index(pfn);
  		unsigned long **mid;
  		unsigned long *mid_mfn_p;
  
  		mid = p2m_top[topidx];
  		mid_mfn_p = p2m_top_mfn_p[topidx];
  
  		/* 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 (mid == p2m_mid_missing) {
  			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) {
  			/*
  			 * XXX boot-time only!  We should never find
  			 * missing parts of the mfn tree after
  			 * runtime.  extend_brk() will BUG if we call
  			 * it too late.
  			 */
  			mid_mfn_p = extend_brk(PAGE_SIZE, PAGE_SIZE);
  			p2m_mid_mfn_init(mid_mfn_p);
  
  			p2m_top_mfn_p[topidx] = mid_mfn_p;
  		}
  
  		p2m_top_mfn[topidx] = virt_to_mfn(mid_mfn_p);
  		mid_mfn_p[mididx] = virt_to_mfn(mid[mididx]);
  	}
  }
  
  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 *mfn_list;
  	unsigned long max_pfn;
  	unsigned long pfn;
  
  	 if (xen_feature(XENFEAT_auto_translated_physmap))
  		return;
  
  	mfn_list = (unsigned long *)xen_start_info->mfn_list;
  	max_pfn = min(MAX_DOMAIN_PAGES, xen_start_info->nr_pages);
  	xen_max_p2m_pfn = max_pfn;
  
  	p2m_missing = extend_brk(PAGE_SIZE, PAGE_SIZE);
  	p2m_init(p2m_missing);
  
  	p2m_mid_missing = extend_brk(PAGE_SIZE, PAGE_SIZE);
  	p2m_mid_init(p2m_mid_missing);
  
  	p2m_top = extend_brk(PAGE_SIZE, PAGE_SIZE);
  	p2m_top_init(p2m_top);
  
  	p2m_identity = extend_brk(PAGE_SIZE, PAGE_SIZE);
  	p2m_init(p2m_identity);
  
  	/*
  	 * The domain builder gives us a pre-constructed p2m array in
  	 * mfn_list for all the pages initially given to us, so we just
  	 * need to graft that into our tree structure.
  	 */
  	for (pfn = 0; pfn < max_pfn; pfn += P2M_PER_PAGE) {
  		unsigned topidx = p2m_top_index(pfn);
  		unsigned mididx = p2m_mid_index(pfn);
  
  		if (p2m_top[topidx] == p2m_mid_missing) {
  			unsigned long **mid = extend_brk(PAGE_SIZE, PAGE_SIZE);
  			p2m_mid_init(mid);
  
  			p2m_top[topidx] = mid;
  		}
  
  		/*
  		 * As long as the mfn_list has enough entries to completely
  		 * fill a p2m page, pointing into the array is ok. But if
  		 * not the entries beyond the last pfn will be undefined.
  		 */
  		if (unlikely(pfn + P2M_PER_PAGE > max_pfn)) {
  			unsigned long p2midx;
  
  			p2midx = max_pfn % P2M_PER_PAGE;
  			for ( ; p2midx < P2M_PER_PAGE; p2midx++)
  				mfn_list[pfn + p2midx] = INVALID_P2M_ENTRY;
  		}
  		p2m_top[topidx][mididx] = &mfn_list[pfn];
  	}
  
  	m2p_override_init();
  }
  #ifdef CONFIG_X86_64
  #include <linux/bootmem.h>
  unsigned long __init xen_revector_p2m_tree(void)
  {
  	unsigned long va_start;
  	unsigned long va_end;
  	unsigned long pfn;
  	unsigned long pfn_free = 0;
  	unsigned long *mfn_list = NULL;
  	unsigned long size;
  
  	va_start = xen_start_info->mfn_list;
  	/*We copy in increments of P2M_PER_PAGE * sizeof(unsigned long),
  	 * so make sure it is rounded up to that */
  	size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
  	va_end = va_start + size;
  
  	/* If we were revectored already, don't do it again. */
  	if (va_start <= __START_KERNEL_map && va_start >= __PAGE_OFFSET)
  		return 0;
  
  	mfn_list = alloc_bootmem_align(size, PAGE_SIZE);
  	if (!mfn_list) {
  		pr_warn("Could not allocate space for a new P2M tree!
  ");
  		return xen_start_info->mfn_list;
  	}
  	/* Fill it out with INVALID_P2M_ENTRY value */
  	memset(mfn_list, 0xFF, size);
  
  	for (pfn = 0; pfn < ALIGN(MAX_DOMAIN_PAGES, P2M_PER_PAGE); pfn += P2M_PER_PAGE) {
  		unsigned topidx = p2m_top_index(pfn);
  		unsigned mididx;
  		unsigned long *mid_p;
  
  		if (!p2m_top[topidx])
  			continue;
  
  		if (p2m_top[topidx] == p2m_mid_missing)
  			continue;
  
  		mididx = p2m_mid_index(pfn);
  		mid_p = p2m_top[topidx][mididx];
  		if (!mid_p)
  			continue;
  		if ((mid_p == p2m_missing) || (mid_p == p2m_identity))
  			continue;
  
  		if ((unsigned long)mid_p == INVALID_P2M_ENTRY)
  			continue;
  
  		/* The old va. Rebase it on mfn_list */
  		if (mid_p >= (unsigned long *)va_start && mid_p <= (unsigned long *)va_end) {
  			unsigned long *new;
  
  			if (pfn_free  > (size / sizeof(unsigned long))) {
  				WARN(1, "Only allocated for %ld pages, but we want %ld!
  ",
  				     size / sizeof(unsigned long), pfn_free);
  				return 0;
  			}
  			new = &mfn_list[pfn_free];
  
  			copy_page(new, mid_p);
  			p2m_top[topidx][mididx] = &mfn_list[pfn_free];
  			p2m_top_mfn_p[topidx][mididx] = virt_to_mfn(&mfn_list[pfn_free]);
  
  			pfn_free += P2M_PER_PAGE;
  
  		}
  		/* This should be the leafs allocated for identity from _brk. */
  	}
  	return (unsigned long)mfn_list;
  
  }
  #else
  unsigned long __init xen_revector_p2m_tree(void)
  {
  	return 0;
  }
  #endif
  unsigned long get_phys_to_machine(unsigned long pfn)
  {
  	unsigned topidx, mididx, idx;
  
  	if (unlikely(pfn >= MAX_P2M_PFN))
  		return INVALID_P2M_ENTRY;
  
  	topidx = p2m_top_index(pfn);
  	mididx = p2m_mid_index(pfn);
  	idx = p2m_index(pfn);
  
  	/*
  	 * The INVALID_P2M_ENTRY is filled in both p2m_*identity
  	 * and in p2m_*missing, so returning the INVALID_P2M_ENTRY
  	 * would be wrong.
  	 */
  	if (p2m_top[topidx][mididx] == p2m_identity)
  		return IDENTITY_FRAME(pfn);
  
  	return p2m_top[topidx][mididx][idx];
  }
  EXPORT_SYMBOL_GPL(get_phys_to_machine);
  
  static void *alloc_p2m_page(void)
  {
  	return (void *)__get_free_page(GFP_KERNEL | __GFP_REPEAT);
  }
  
  static void free_p2m_page(void *p)
  {
  	free_page((unsigned long)p);
  }
  
  /*
   * 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_p, **mid;
  	unsigned long *top_mfn_p, *mid_mfn;
  
  	topidx = p2m_top_index(pfn);
  	mididx = p2m_mid_index(pfn);
  
  	top_p = &p2m_top[topidx];
  	mid = *top_p;
  
  	if (mid == p2m_mid_missing) {
  		/* Mid level is missing, allocate a new one */
  		mid = alloc_p2m_page();
  		if (!mid)
  			return false;
  
  		p2m_mid_init(mid);
  
  		if (cmpxchg(top_p, p2m_mid_missing, mid) != p2m_mid_missing)
  			free_p2m_page(mid);
  	}
  
  	top_mfn_p = &p2m_top_mfn[topidx];
  	mid_mfn = 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;
  
  		mid_mfn = alloc_p2m_page();
  		if (!mid_mfn)
  			return false;
  
  		p2m_mid_mfn_init(mid_mfn);
  
  		missing_mfn = virt_to_mfn(p2m_mid_missing_mfn);
  		mid_mfn_mfn = virt_to_mfn(mid_mfn);
  		if (cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn) != missing_mfn)
  			free_p2m_page(mid_mfn);
  		else
  			p2m_top_mfn_p[topidx] = mid_mfn;
  	}
  
  	if (p2m_top[topidx][mididx] == p2m_identity ||
  	    p2m_top[topidx][mididx] == p2m_missing) {
  		/* p2m leaf page is missing */
  		unsigned long *p2m;
  		unsigned long *p2m_orig = p2m_top[topidx][mididx];
  
  		p2m = alloc_p2m_page();
  		if (!p2m)
  			return false;
  
  		p2m_init(p2m);
  
  		if (cmpxchg(&mid[mididx], p2m_orig, p2m) != p2m_orig)
  			free_p2m_page(p2m);
  		else
  			mid_mfn[mididx] = virt_to_mfn(p2m);
  	}
  
  	return true;
  }
  
  static bool __init early_alloc_p2m_middle(unsigned long pfn, bool check_boundary)
  {
  	unsigned topidx, mididx, idx;
  	unsigned long *p2m;
  	unsigned long *mid_mfn_p;
  
  	topidx = p2m_top_index(pfn);
  	mididx = p2m_mid_index(pfn);
  	idx = p2m_index(pfn);
  
  	/* Pfff.. No boundary cross-over, lets get out. */
  	if (!idx && check_boundary)
  		return false;
  
  	WARN(p2m_top[topidx][mididx] == p2m_identity,
  		"P2M[%d][%d] == IDENTITY, should be MISSING (or alloced)!
  ",
  		topidx, mididx);
  
  	/*
  	 * Could be done by xen_build_dynamic_phys_to_machine..
  	 */
  	if (p2m_top[topidx][mididx] != p2m_missing)
  		return false;
  
  	/* Boundary cross-over for the edges: */
  	p2m = extend_brk(PAGE_SIZE, PAGE_SIZE);
  
  	p2m_init(p2m);
  
  	p2m_top[topidx][mididx] = p2m;
  
  	/* For save/restore we need to MFN of the P2M saved */
  
  	mid_mfn_p = p2m_top_mfn_p[topidx];
  	WARN(mid_mfn_p[mididx] != virt_to_mfn(p2m_missing),
  		"P2M_TOP_P[%d][%d] != MFN of p2m_missing!
  ",
  		topidx, mididx);
  	mid_mfn_p[mididx] = virt_to_mfn(p2m);
  
  	return true;
  }
  
  static bool __init early_alloc_p2m(unsigned long pfn)
  {
  	unsigned topidx = p2m_top_index(pfn);
  	unsigned long *mid_mfn_p;
  	unsigned long **mid;
  
  	mid = p2m_top[topidx];
  	mid_mfn_p = p2m_top_mfn_p[topidx];
  	if (mid == p2m_mid_missing) {
  		mid = extend_brk(PAGE_SIZE, PAGE_SIZE);
  
  		p2m_mid_init(mid);
  
  		p2m_top[topidx] = mid;
  
  		BUG_ON(mid_mfn_p != p2m_mid_missing_mfn);
  	}
  	/* And the save/restore P2M tables.. */
  	if (mid_mfn_p == p2m_mid_missing_mfn) {
  		mid_mfn_p = extend_brk(PAGE_SIZE, PAGE_SIZE);
  		p2m_mid_mfn_init(mid_mfn_p);
  
  		p2m_top_mfn_p[topidx] = mid_mfn_p;
  		p2m_top_mfn[topidx] = virt_to_mfn(mid_mfn_p);
  		/* Note: we don't set mid_mfn_p[midix] here,
  		 * look in early_alloc_p2m_middle */
  	}
  	return true;
  }
  
  /*
   * Skim over the P2M tree looking at pages that are either filled with
   * INVALID_P2M_ENTRY or with 1:1 PFNs. If found, re-use that page and
   * replace the P2M leaf with a p2m_missing or p2m_identity.
   * Stick the old page in the new P2M tree location.
   */
  bool __init early_can_reuse_p2m_middle(unsigned long set_pfn, unsigned long set_mfn)
  {
  	unsigned topidx;
  	unsigned mididx;
  	unsigned ident_pfns;
  	unsigned inv_pfns;
  	unsigned long *p2m;
  	unsigned long *mid_mfn_p;
  	unsigned idx;
  	unsigned long pfn;
  
  	/* We only look when this entails a P2M middle layer */
  	if (p2m_index(set_pfn))
  		return false;
  
  	for (pfn = 0; pfn < MAX_DOMAIN_PAGES; pfn += P2M_PER_PAGE) {
  		topidx = p2m_top_index(pfn);
  
  		if (!p2m_top[topidx])
  			continue;
  
  		if (p2m_top[topidx] == p2m_mid_missing)
  			continue;
  
  		mididx = p2m_mid_index(pfn);
  		p2m = p2m_top[topidx][mididx];
  		if (!p2m)
  			continue;
  
  		if ((p2m == p2m_missing) || (p2m == p2m_identity))
  			continue;
  
  		if ((unsigned long)p2m == INVALID_P2M_ENTRY)
  			continue;
  
  		ident_pfns = 0;
  		inv_pfns = 0;
  		for (idx = 0; idx < P2M_PER_PAGE; idx++) {
  			/* IDENTITY_PFNs are 1:1 */
  			if (p2m[idx] == IDENTITY_FRAME(pfn + idx))
  				ident_pfns++;
  			else if (p2m[idx] == INVALID_P2M_ENTRY)
  				inv_pfns++;
  			else
  				break;
  		}
  		if ((ident_pfns == P2M_PER_PAGE) || (inv_pfns == P2M_PER_PAGE))
  			goto found;
  	}
  	return false;
  found:
  	/* Found one, replace old with p2m_identity or p2m_missing */
  	p2m_top[topidx][mididx] = (ident_pfns ? p2m_identity : p2m_missing);
  	/* And the other for save/restore.. */
  	mid_mfn_p = p2m_top_mfn_p[topidx];
  	/* NOTE: Even if it is a p2m_identity it should still be point to
  	 * a page filled with INVALID_P2M_ENTRY entries. */
  	mid_mfn_p[mididx] = virt_to_mfn(p2m_missing);
  
  	/* Reset where we want to stick the old page in. */
  	topidx = p2m_top_index(set_pfn);
  	mididx = p2m_mid_index(set_pfn);
  
  	/* This shouldn't happen */
  	if (WARN_ON(p2m_top[topidx] == p2m_mid_missing))
  		early_alloc_p2m(set_pfn);
  
  	if (WARN_ON(p2m_top[topidx][mididx] != p2m_missing))
  		return false;
  
  	p2m_init(p2m);
  	p2m_top[topidx][mididx] = p2m;
  	mid_mfn_p = p2m_top_mfn_p[topidx];
  	mid_mfn_p[mididx] = virt_to_mfn(p2m);
  
  	return true;
  }
  bool __init early_set_phys_to_machine(unsigned long pfn, unsigned long mfn)
  {
  	if (unlikely(!__set_phys_to_machine(pfn, mfn)))  {
  		if (!early_alloc_p2m(pfn))
  			return false;
  
  		if (early_can_reuse_p2m_middle(pfn, mfn))
  			return __set_phys_to_machine(pfn, mfn);
  
  		if (!early_alloc_p2m_middle(pfn, false /* boundary crossover OK!*/))
  			return false;
  
  		if (!__set_phys_to_machine(pfn, mfn))
  			return false;
  	}
  
  	return true;
  }
  unsigned long __init set_phys_range_identity(unsigned long pfn_s,
  				      unsigned long pfn_e)
  {
  	unsigned long pfn;
  
  	if (unlikely(pfn_s >= MAX_P2M_PFN || pfn_e >= MAX_P2M_PFN))
  		return 0;
  
  	if (unlikely(xen_feature(XENFEAT_auto_translated_physmap)))
  		return pfn_e - pfn_s;
  
  	if (pfn_s > pfn_e)
  		return 0;
  
  	for (pfn = (pfn_s & ~(P2M_MID_PER_PAGE * P2M_PER_PAGE - 1));
  		pfn < ALIGN(pfn_e, (P2M_MID_PER_PAGE * P2M_PER_PAGE));
  		pfn += P2M_MID_PER_PAGE * P2M_PER_PAGE)
  	{
  		WARN_ON(!early_alloc_p2m(pfn));
  	}
  
  	early_alloc_p2m_middle(pfn_s, true);
  	early_alloc_p2m_middle(pfn_e, true);
  
  	for (pfn = pfn_s; pfn < pfn_e; pfn++)
  		if (!__set_phys_to_machine(pfn, IDENTITY_FRAME(pfn)))
  			break;
  
  	if (!WARN((pfn - pfn_s) != (pfn_e - pfn_s),
  		"Identity mapping failed. We are %ld short of 1-1 mappings!
  ",
  		(pfn_e - pfn_s) - (pfn - pfn_s)))
  		printk(KERN_DEBUG "1-1 mapping on %lx->%lx
  ", pfn_s, pfn);
  
  	return pfn - pfn_s;
  }
  
  /* Try to install p2m mapping; fail if intermediate bits missing */
  bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
  {
  	unsigned topidx, mididx, idx;
  
  	/* don't track P2M changes in autotranslate guests */
  	if (unlikely(xen_feature(XENFEAT_auto_translated_physmap)))
  		return true;
  
  	if (unlikely(pfn >= MAX_P2M_PFN)) {
  		BUG_ON(mfn != INVALID_P2M_ENTRY);
  		return true;
  	}
  
  	topidx = p2m_top_index(pfn);
  	mididx = p2m_mid_index(pfn);
  	idx = p2m_index(pfn);
  
  	/* For sparse holes were the p2m leaf has real PFN along with
  	 * PCI holes, stick in the PFN as the MFN value.
  	 */
  	if (mfn != INVALID_P2M_ENTRY && (mfn & IDENTITY_FRAME_BIT)) {
  		if (p2m_top[topidx][mididx] == p2m_identity)
  			return true;
  
  		/* Swap over from MISSING to IDENTITY if needed. */
  		if (p2m_top[topidx][mididx] == p2m_missing) {
  			WARN_ON(cmpxchg(&p2m_top[topidx][mididx], p2m_missing,
  				p2m_identity) != p2m_missing);
  			return true;
  		}
  	}
  
  	if (p2m_top[topidx][mididx] == p2m_missing)
  		return mfn == INVALID_P2M_ENTRY;
  
  	p2m_top[topidx][mididx][idx] = mfn;
  
  	return true;
  }
  
  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;
  
  		if (!__set_phys_to_machine(pfn, mfn))
  			return false;
  	}
  
  	return true;
  }
  
  #define M2P_OVERRIDE_HASH_SHIFT	10
  #define M2P_OVERRIDE_HASH	(1 << M2P_OVERRIDE_HASH_SHIFT)
  
  static RESERVE_BRK_ARRAY(struct list_head, m2p_overrides, M2P_OVERRIDE_HASH);
  static DEFINE_SPINLOCK(m2p_override_lock);
  
  static void __init m2p_override_init(void)
  {
  	unsigned i;
  
  	m2p_overrides = extend_brk(sizeof(*m2p_overrides) * M2P_OVERRIDE_HASH,
  				   sizeof(unsigned long));
  
  	for (i = 0; i < M2P_OVERRIDE_HASH; i++)
  		INIT_LIST_HEAD(&m2p_overrides[i]);
  }
  
  static unsigned long mfn_hash(unsigned long mfn)
  {
  	return hash_long(mfn, M2P_OVERRIDE_HASH_SHIFT);
  }
  
  /* Add an MFN override for a particular page */
  int m2p_add_override(unsigned long mfn, struct page *page,
  		struct gnttab_map_grant_ref *kmap_op)
  {
  	unsigned long flags;
  	unsigned long pfn;
  	unsigned long uninitialized_var(address);
  	unsigned level;
  	pte_t *ptep = NULL;
  
  	pfn = page_to_pfn(page);
  	if (!PageHighMem(page)) {
  		address = (unsigned long)__va(pfn << PAGE_SHIFT);
  		ptep = lookup_address(address, &level);
  		if (WARN(ptep == NULL || level != PG_LEVEL_4K,
  					"m2p_add_override: pfn %lx not mapped", pfn))
  			return -EINVAL;
  	}
  	WARN_ON(PagePrivate(page));
  	SetPagePrivate(page);
  	set_page_private(page, mfn);
  	page->index = pfn_to_mfn(pfn);
  
  	if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn))))
  		return -ENOMEM;
  
  	if (kmap_op != NULL) {
  		if (!PageHighMem(page)) {
  			struct multicall_space mcs =
  				xen_mc_entry(sizeof(*kmap_op));
  
  			MULTI_grant_table_op(mcs.mc,
  					GNTTABOP_map_grant_ref, kmap_op, 1);
  
  			xen_mc_issue(PARAVIRT_LAZY_MMU);
  		}
  	}
  	spin_lock_irqsave(&m2p_override_lock, flags);
  	list_add(&page->lru,  &m2p_overrides[mfn_hash(mfn)]);
  	spin_unlock_irqrestore(&m2p_override_lock, flags);
  
  	/* p2m(m2p(mfn)) == mfn: the mfn is already present somewhere in
  	 * this domain. Set the FOREIGN_FRAME_BIT in the p2m for the other
  	 * pfn so that the following mfn_to_pfn(mfn) calls will return the
  	 * pfn from the m2p_override (the backend pfn) instead.
  	 * We need to do this because the pages shared by the frontend
  	 * (xen-blkfront) can be already locked (lock_page, called by
  	 * do_read_cache_page); when the userspace backend tries to use them
  	 * with direct_IO, mfn_to_pfn returns the pfn of the frontend, so
  	 * do_blockdev_direct_IO is going to try to lock the same pages
  	 * again resulting in a deadlock.
  	 * As a side effect get_user_pages_fast might not be safe on the
  	 * frontend pages while they are being shared with the backend,
  	 * because mfn_to_pfn (that ends up being called by GUPF) will
  	 * return the backend pfn rather than the frontend pfn. */
  	pfn = mfn_to_pfn_no_overrides(mfn);
  	if (get_phys_to_machine(pfn) == mfn)
  		set_phys_to_machine(pfn, FOREIGN_FRAME(mfn));
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(m2p_add_override);
  int m2p_remove_override(struct page *page,
  		struct gnttab_map_grant_ref *kmap_op)
  {
  	unsigned long flags;
  	unsigned long mfn;
  	unsigned long pfn;
  	unsigned long uninitialized_var(address);
  	unsigned level;
  	pte_t *ptep = NULL;
  
  	pfn = page_to_pfn(page);
  	mfn = get_phys_to_machine(pfn);
  	if (mfn == INVALID_P2M_ENTRY || !(mfn & FOREIGN_FRAME_BIT))
  		return -EINVAL;
  
  	if (!PageHighMem(page)) {
  		address = (unsigned long)__va(pfn << PAGE_SHIFT);
  		ptep = lookup_address(address, &level);
  
  		if (WARN(ptep == NULL || level != PG_LEVEL_4K,
  					"m2p_remove_override: pfn %lx not mapped", pfn))
  			return -EINVAL;
  	}
  
  	spin_lock_irqsave(&m2p_override_lock, flags);
  	list_del(&page->lru);
  	spin_unlock_irqrestore(&m2p_override_lock, flags);
  	WARN_ON(!PagePrivate(page));
  	ClearPagePrivate(page);
  
  	set_phys_to_machine(pfn, page->index);
  	if (kmap_op != NULL) {
  		if (!PageHighMem(page)) {
  			struct multicall_space mcs;
  			struct gnttab_unmap_and_replace *unmap_op;
  			struct page *scratch_page = get_balloon_scratch_page();
  			unsigned long scratch_page_address = (unsigned long)
  				__va(page_to_pfn(scratch_page) << PAGE_SHIFT);
  
  			/*
  			 * It might be that we queued all the m2p grant table
  			 * hypercalls in a multicall, then m2p_remove_override
  			 * get called before the multicall has actually been
  			 * issued. In this case handle is going to -1 because
  			 * it hasn't been modified yet.
  			 */
  			if (kmap_op->handle == -1)
  				xen_mc_flush();
  			/*
  			 * Now if kmap_op->handle is negative it means that the
  			 * hypercall actually returned an error.
  			 */
  			if (kmap_op->handle == GNTST_general_error) {
  				printk(KERN_WARNING "m2p_remove_override: "
  						"pfn %lx mfn %lx, failed to modify kernel mappings",
  						pfn, mfn);
  				put_balloon_scratch_page();
  				return -1;
  			}
  
  			xen_mc_batch();
  
  			mcs = __xen_mc_entry(
  					sizeof(struct gnttab_unmap_and_replace));
  			unmap_op = mcs.args;
  			unmap_op->host_addr = kmap_op->host_addr;
  			unmap_op->new_addr = scratch_page_address;
  			unmap_op->handle = kmap_op->handle;
  
  			MULTI_grant_table_op(mcs.mc,
  					GNTTABOP_unmap_and_replace, unmap_op, 1);
  
  			mcs = __xen_mc_entry(0);
  			MULTI_update_va_mapping(mcs.mc, scratch_page_address,
  					pfn_pte(page_to_pfn(scratch_page),
  					PAGE_KERNEL_RO), 0);
  
  			xen_mc_issue(PARAVIRT_LAZY_MMU);
  
  			kmap_op->host_addr = 0;
  			put_balloon_scratch_page();
  		}
  	}
  
  	/* p2m(m2p(mfn)) == FOREIGN_FRAME(mfn): the mfn is already present
  	 * somewhere in this domain, even before being added to the
  	 * m2p_override (see comment above in m2p_add_override).
  	 * If there are no other entries in the m2p_override corresponding
  	 * to this mfn, then remove the FOREIGN_FRAME_BIT from the p2m for
  	 * the original pfn (the one shared by the frontend): the backend
  	 * cannot do any IO on this page anymore because it has been
  	 * unshared. Removing the FOREIGN_FRAME_BIT from the p2m entry of
  	 * the original pfn causes mfn_to_pfn(mfn) to return the frontend
  	 * pfn again. */
  	mfn &= ~FOREIGN_FRAME_BIT;
  	pfn = mfn_to_pfn_no_overrides(mfn);
  	if (get_phys_to_machine(pfn) == FOREIGN_FRAME(mfn) &&
  			m2p_find_override(mfn) == NULL)
  		set_phys_to_machine(pfn, mfn);
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(m2p_remove_override);
  
  struct page *m2p_find_override(unsigned long mfn)
  {
  	unsigned long flags;
  	struct list_head *bucket = &m2p_overrides[mfn_hash(mfn)];
  	struct page *p, *ret;
  
  	ret = NULL;
  
  	spin_lock_irqsave(&m2p_override_lock, flags);
  
  	list_for_each_entry(p, bucket, lru) {
  		if (page_private(p) == mfn) {
  			ret = p;
  			break;
  		}
  	}
  
  	spin_unlock_irqrestore(&m2p_override_lock, flags);
  
  	return ret;
  }
  
  unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn)
  {
  	struct page *p = m2p_find_override(mfn);
  	unsigned long ret = pfn;
  
  	if (p)
  		ret = page_to_pfn(p);
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(m2p_find_override_pfn);
  
  #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 level_name[] = { "top", "middle",
  						"entry", "abnormal", "error"};
  #define TYPE_IDENTITY 0
  #define TYPE_MISSING 1
  #define TYPE_PFN 2
  #define TYPE_UNKNOWN 3
  	static const char * const type_name[] = {
  				[TYPE_IDENTITY] = "identity",
  				[TYPE_MISSING] = "missing",
  				[TYPE_PFN] = "pfn",
  				[TYPE_UNKNOWN] = "abnormal"};
  	unsigned long pfn, prev_pfn_type = 0, prev_pfn_level = 0;
  	unsigned int uninitialized_var(prev_level);
  	unsigned int uninitialized_var(prev_type);
  
  	if (!p2m_top)
  		return 0;
  
  	for (pfn = 0; pfn < MAX_DOMAIN_PAGES; pfn++) {
  		unsigned topidx = p2m_top_index(pfn);
  		unsigned mididx = p2m_mid_index(pfn);
  		unsigned idx = p2m_index(pfn);
  		unsigned lvl, type;
  
  		lvl = 4;
  		type = TYPE_UNKNOWN;
  		if (p2m_top[topidx] == p2m_mid_missing) {
  			lvl = 0; type = TYPE_MISSING;
  		} else if (p2m_top[topidx] == NULL) {
  			lvl = 0; type = TYPE_UNKNOWN;
  		} else if (p2m_top[topidx][mididx] == NULL) {
  			lvl = 1; type = TYPE_UNKNOWN;
  		} else if (p2m_top[topidx][mididx] == p2m_identity) {
  			lvl = 1; type = TYPE_IDENTITY;
  		} else if (p2m_top[topidx][mididx] == p2m_missing) {
  			lvl = 1; type = TYPE_MISSING;
  		} else if (p2m_top[topidx][mididx][idx] == 0) {
  			lvl = 2; type = TYPE_UNKNOWN;
  		} else if (p2m_top[topidx][mididx][idx] == IDENTITY_FRAME(pfn)) {
  			lvl = 2; type = TYPE_IDENTITY;
  		} else if (p2m_top[topidx][mididx][idx] == INVALID_P2M_ENTRY) {
  			lvl = 2; type = TYPE_MISSING;
  		} else if (p2m_top[topidx][mididx][idx] == pfn) {
  			lvl = 2; type = TYPE_PFN;
  		} else if (p2m_top[topidx][mididx][idx] != pfn) {
  			lvl = 2; type = TYPE_PFN;
  		}
  		if (pfn == 0) {
  			prev_level = lvl;
  			prev_type = type;
  		}
  		if (pfn == MAX_DOMAIN_PAGES-1) {
  			lvl = 3;
  			type = TYPE_UNKNOWN;
  		}
  		if (prev_type != type) {
  			seq_printf(m, " [0x%lx->0x%lx] %s
  ",
  				prev_pfn_type, pfn, type_name[prev_type]);
  			prev_pfn_type = pfn;
  			prev_type = type;
  		}
  		if (prev_level != lvl) {
  			seq_printf(m, " [0x%lx->0x%lx] level %s
  ",
  				prev_pfn_level, pfn, level_name[prev_level]);
  			prev_pfn_level = pfn;
  			prev_level = lvl;
  		}
  	}
  	return 0;
  #undef TYPE_IDENTITY
  #undef TYPE_MISSING
  #undef TYPE_PFN
  #undef TYPE_UNKNOWN
  }
  
  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 */