p2m.c

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/*
 * 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/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;

    /* 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)
{
    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 *)xen_start_info->mfn_list;
    unsigned long max_pfn = min(MAX_DOMAIN_PAGES, xen_start_info->nr_pages);
    unsigned long pfn;

    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!\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];
            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)!\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;

    /* 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!\n",
        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!\n",
        (pfn_e - pfn_s) - (pfn - pfn_s)))
        printk(KERN_DEBUG "1-1 mapping on %lx->%lx\n", 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;

    if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
        BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
        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;
    int ret = 0;

    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. */
    ret = __get_user(pfn, &machine_to_phys_mapping[mfn]);
    if (ret == 0 && 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;
    int ret = 0;

    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_grant_ref *unmap_op;

            /*
             * 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);
                return -1;
            }

            mcs = xen_mc_entry(
                    sizeof(struct gnttab_unmap_grant_ref));
            unmap_op = mcs.args;
            unmap_op->host_addr = kmap_op->host_addr;
            unmap_op->handle = kmap_op->handle;
            unmap_op->dev_bus_addr = 0;

            MULTI_grant_table_op(mcs.mc,
                    GNTTABOP_unmap_grant_ref, unmap_op, 1);

            xen_mc_issue(PARAVIRT_LAZY_MMU);

            set_pte_at(&init_mm, address, ptep,
                    pfn_pte(pfn, PAGE_KERNEL));
            __flush_tlb_single(address);
            kmap_op->host_addr = 0;
        }
    }

    /* 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;
    ret = __get_user(pfn, &machine_to_phys_mapping[mfn]);
    if (ret == 0 && 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 */