arch/x86/xen/p2m.c

/*
 * 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 because 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    4GB
 * /-------------------+---------\/----\         /----------\    /---+-----\
 * | 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 reserve_brk new middle and leaf pages as
 * required to split any existing p2m_mid_missing middle pages.
 *
 * 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 (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 entry is pointing to p2m_missing we can swap it
 * over to p2m_identity - this way covering 4MB (or 2MB) PFN space (and
 * similarly swapping p2m_mid_missing for p2m_mid_identity for larger regions).
 * 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."
 *
 * Finally, the region beyond the end of of the E820 (4 GB in this example)
 * is set to be identity (in case there are MMIO regions placed here).
 *
 * 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 [1]
 *  |-----|  \  \-------------------->/---------------\   /-----------------\
 *  | ..  |\  |                       | [p2m_identity]+-->| ~0, ~0, ~0, ... |
 *  \-----/ | |                       | [p2m_identity]+-->| ..., ~0         |
 *          | |                       | ....          |   \-----------------/
 *          | |                       +-[x], ~0, ~0.. +\
 *          | |                       \---------------/ \
 *          | |                                          \-> /---------------\
 *          | V  p2m_mid_missing       p2m_missing           | IDENTITY[@0]  |
 *          | /-----------------\     /------------\         | IDENTITY[@256]|
 *          | | [p2m_missing]   +---->| ~0, ~0, ...|         | ~0, ~0, ....  |
 *          | | [p2m_missing]   +---->| ..., ~0    |         \---------------/
 *          | | ...             |     \------------/
 *          | \-----------------/
 *          |
 *          |     p2m_mid_identity
 *          |   /-----------------\
 *          \-->| [p2m_identity]  +---->[1]
 *              | [p2m_identity]  +---->[1]
 *              | ...             |
 *              \-----------------/
 *
 * 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 <linux/bootmem.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 "p2m.h"
#include "multicalls.h"
#include "xen-ops.h"

static void __init m2p_override_init(void);

unsigned long xen_max_p2m_pfn __read_mostly;

static unsigned long *p2m_mid_missing_mfn;
static unsigned long *p2m_top_mfn;
static unsigned long **p2m_top_mfn_p;

/* 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_top, P2M_TOP_PER_PAGE);

static RESERVE_BRK_ARRAY(unsigned long, p2m_identity, P2M_PER_PAGE);
static RESERVE_BRK_ARRAY(unsigned long *, p2m_mid_identity, P2M_MID_PER_PAGE);

RESERVE_BRK(p2m_mid, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID_PER_PAGE)));

/* For each I/O range remapped we may lose up to two leaf pages for the boundary
 * violations and three mid pages to cover up to 3GB. With
 * early_can_reuse_p2m_middle() most of the leaf pages will be reused by the
 * remapped region.
 */
RESERVE_BRK(p2m_identity_remap, PAGE_SIZE * 2 * 3 * MAX_REMAP_RANGES);

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 long *leaf)
{
	unsigned i;

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

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_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 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;

	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_bootmem_align(PAGE_SIZE, PAGE_SIZE);
		p2m_mid_mfn_init(p2m_mid_missing_mfn, p2m_missing);

		p2m_top_mfn_p = alloc_bootmem_align(PAGE_SIZE, PAGE_SIZE);
		p2m_top_mfn_p_init(p2m_top_mfn_p);

		p2m_top_mfn = alloc_bootmem_align(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, p2m_missing);
	}

	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.
			 */
			mid_mfn_p = alloc_bootmem_align(PAGE_SIZE, PAGE_SIZE);
			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] = 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_identity = extend_brk(PAGE_SIZE, PAGE_SIZE);
	p2m_init(p2m_identity);

	p2m_mid_missing = extend_brk(PAGE_SIZE, PAGE_SIZE);
	p2m_mid_init(p2m_mid_missing, p2m_missing);
	p2m_mid_identity = extend_brk(PAGE_SIZE, PAGE_SIZE);
	p2m_mid_init(p2m_mid_identity, p2m_identity);

	p2m_top = extend_brk(PAGE_SIZE, PAGE_SIZE);
	p2m_top_init(p2m_top);

	/*
	 * 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_missing);

			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
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!\n");
		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!\n",
				     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];

			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 IDENTITY_FRAME(pfn);

	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, p2m_missing);

		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;
		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;
		}
	}

	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(unsigned long pfn, bool check_boundary)
{
	unsigned topidx, mididx, idx;
	unsigned long *p2m;

	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)!\n",
		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;

	return true;
}

static bool __init early_alloc_p2m_middle(unsigned long pfn)
{
	unsigned topidx = p2m_top_index(pfn);
	unsigned long **mid;

	mid = p2m_top[topidx];
	if (mid == p2m_mid_missing) {
		mid = extend_brk(PAGE_SIZE, PAGE_SIZE);

		p2m_mid_init(mid, p2m_missing);

		p2m_top[topidx] = mid;
	}
	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.
 */
static bool __init early_can_reuse_p2m_middle(unsigned long set_pfn)
{
	unsigned topidx;
	unsigned mididx;
	unsigned ident_pfns;
	unsigned inv_pfns;
	unsigned long *p2m;
	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);

	/* 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_middle(set_pfn);

	if (WARN_ON(p2m_top[topidx][mididx] != p2m_missing))
		return false;

	p2m_init(p2m);
	p2m_top[topidx][mididx] = 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_middle(pfn))
			return false;

		if (early_can_reuse_p2m_middle(pfn))
			return __set_phys_to_machine(pfn, mfn);

		if (!early_alloc_p2m(pfn, false /* boundary crossover OK!*/))
			return false;

		if (!__set_phys_to_machine(pfn, mfn))
			return false;
	}

	return true;
}

static void __init early_split_p2m(unsigned long pfn)
{
	unsigned long mididx, idx;

	mididx = p2m_mid_index(pfn);
	idx = p2m_index(pfn);

	/*
	 * Allocate new middle and leaf pages if this pfn lies in the
	 * middle of one.
	 */
	if (mididx || idx)
		early_alloc_p2m_middle(pfn);
	if (idx)
		early_alloc_p2m(pfn, false);
}

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))
		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 > MAX_P2M_PFN)
		pfn_e = MAX_P2M_PFN;

	early_split_p2m(pfn_s);
	early_split_p2m(pfn_e);

	for (pfn = pfn_s; pfn < pfn_e;) {
		unsigned topidx = p2m_top_index(pfn);
		unsigned mididx = p2m_mid_index(pfn);

		if (!__set_phys_to_machine(pfn, IDENTITY_FRAME(pfn)))
			break;
		pfn++;

		/*
		 * If the PFN was set to a middle or leaf identity
		 * page the remainder must also be identity, so skip
		 * ahead to the next middle or leaf entry.
		 */
		if (p2m_top[topidx] == p2m_mid_identity)
			pfn = ALIGN(pfn, P2M_MID_PER_PAGE * P2M_PER_PAGE);
		else if (p2m_top[topidx][mididx] == p2m_identity)
			pfn = ALIGN(pfn, P2M_PER_PAGE);
	}

	WARN((pfn - pfn_s) != (pfn_e - pfn_s),
		"Identity mapping failed. We are %ld short of 1-1 mappings!\n",
		(pfn_e - pfn_s) - (pfn - pfn_s));

	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.
	 *
	 * set_phys_range_identity() will have allocated new middle
	 * and leaf pages as required so an existing p2m_mid_missing
	 * or p2m_missing mean that whole range will be identity so
	 * these can be switched to p2m_mid_identity or p2m_identity.
	 */
	if (mfn != INVALID_P2M_ENTRY && (mfn & IDENTITY_FRAME_BIT)) {
		if (p2m_top[topidx] == p2m_mid_identity)
			return true;

		if (p2m_top[topidx] == p2m_mid_missing) {
			WARN_ON(cmpxchg(&p2m_top[topidx], p2m_mid_missing,
					p2m_mid_identity) != p2m_mid_missing);
			return true;
		}

		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);
}

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;
	bool lazy = false;
	pte_t *pte;

	if (xen_feature(XENFEAT_auto_translated_physmap))
		return 0;

	if (kmap_ops &&
	    !in_interrupt() &&
	    paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
		arch_enter_lazy_mmu_mode();
		lazy = true;
	}

	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_ON(PagePrivate(pages[i]));
		SetPagePrivate(pages[i]);
		set_page_private(pages[i], mfn);
		pages[i]->index = pfn_to_mfn(pfn);

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

		if (kmap_ops) {
			ret = m2p_add_override(mfn, pages[i], &kmap_ops[i]);
			if (ret)
				goto out;
		}
	}

out:
	if (lazy)
		arch_leave_lazy_mmu_mode();

	return ret;
}
EXPORT_SYMBOL_GPL(set_foreign_p2m_mapping);

/* 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;
	}

	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 clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref *unmap_ops,
			      struct gnttab_map_grant_ref *kmap_ops,
			      struct page **pages, unsigned int count)
{
	int i, ret = 0;
	bool lazy = false;

	if (xen_feature(XENFEAT_auto_translated_physmap))
		return 0;

	if (kmap_ops &&
	    !in_interrupt() &&
	    paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
		arch_enter_lazy_mmu_mode();
		lazy = true;
	}

	for (i = 0; i < count; i++) {
		unsigned long mfn = get_phys_to_machine(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_page_private(pages[i], INVALID_P2M_ENTRY);
		WARN_ON(!PagePrivate(pages[i]));
		ClearPagePrivate(pages[i]);
		set_phys_to_machine(pfn, pages[i]->index);

		if (kmap_ops)
			ret = m2p_remove_override(pages[i], &kmap_ops[i], mfn);
		if (ret)
			goto out;
	}

out:
	if (lazy)
		arch_leave_lazy_mmu_mode();
	return ret;
}
EXPORT_SYMBOL_GPL(clear_foreign_p2m_mapping);

int m2p_remove_override(struct page *page,
			struct gnttab_map_grant_ref *kmap_op,
			unsigned long mfn)
{
	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_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);

	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\n",
				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\n",
				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 */