grant-table.c

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/******************************************************************************
 * grant_table.c
 *
 * Granting foreign access to our memory reservation.
 *
 * Copyright (c) 2005-2006, Christopher Clark
 * Copyright (c) 2004-2005, K A Fraser
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>
#include <linux/io.h>
#include <linux/delay.h>
#include <linux/hardirq.h>

#include <xen/xen.h>
#include <xen/interface/xen.h>
#include <xen/page.h>
#include <xen/grant_table.h>
#include <xen/interface/memory.h>
#include <xen/hvc-console.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/interface.h>

#include <asm/pgtable.h>
#include <asm/sync_bitops.h>

/* External tools reserve first few grant table entries. */
#define NR_RESERVED_ENTRIES 8
#define GNTTAB_LIST_END 0xffffffff
#define GREFS_PER_GRANT_FRAME \
(grant_table_version == 1 ?                      \
(PAGE_SIZE / sizeof(struct grant_entry_v1)) :   \
(PAGE_SIZE / sizeof(union grant_entry_v2)))

static grant_ref_t **gnttab_list;
static unsigned int nr_grant_frames;
static unsigned int boot_max_nr_grant_frames;
static int gnttab_free_count;
static grant_ref_t gnttab_free_head;
static DEFINE_SPINLOCK(gnttab_list_lock);
unsigned long xen_hvm_resume_frames;
EXPORT_SYMBOL_GPL(xen_hvm_resume_frames);

static union {
    struct grant_entry_v1 *v1;
    union grant_entry_v2 *v2;
    void *addr;
} gnttab_shared;

/*This is a structure of function pointers for grant table*/
struct gnttab_ops {
    /*
     * Mapping a list of frames for storing grant entries. Frames parameter
     * is used to store grant table address when grant table being setup,
     * nr_gframes is the number of frames to map grant table. Returning
     * GNTST_okay means success and negative value means failure.
     */
    int (*map_frames)(xen_pfn_t *frames, unsigned int nr_gframes);
    /*
     * Release a list of frames which are mapped in map_frames for grant
     * entry status.
     */
    void (*unmap_frames)(void);
    /*
     * Introducing a valid entry into the grant table, granting the frame of
     * this grant entry to domain for accessing or transfering. Ref
     * parameter is reference of this introduced grant entry, domid is id of
     * granted domain, frame is the page frame to be granted, and flags is
     * status of the grant entry to be updated.
     */
    void (*update_entry)(grant_ref_t ref, domid_t domid,
                 unsigned long frame, unsigned flags);
    /*
     * Stop granting a grant entry to domain for accessing. Ref parameter is
     * reference of a grant entry whose grant access will be stopped,
     * readonly is not in use in this function. If the grant entry is
     * currently mapped for reading or writing, just return failure(==0)
     * directly and don't tear down the grant access. Otherwise, stop grant
     * access for this entry and return success(==1).
     */
    int (*end_foreign_access_ref)(grant_ref_t ref, int readonly);
    /*
     * Stop granting a grant entry to domain for transfer. Ref parameter is
     * reference of a grant entry whose grant transfer will be stopped. If
     * tranfer has not started, just reclaim the grant entry and return
     * failure(==0). Otherwise, wait for the transfer to complete and then
     * return the frame.
     */
    unsigned long (*end_foreign_transfer_ref)(grant_ref_t ref);
    /*
     * Query the status of a grant entry. Ref parameter is reference of
     * queried grant entry, return value is the status of queried entry.
     * Detailed status(writing/reading) can be gotten from the return value
     * by bit operations.
     */
    int (*query_foreign_access)(grant_ref_t ref);
    /*
     * Grant a domain to access a range of bytes within the page referred by
     * an available grant entry. Ref parameter is reference of a grant entry
     * which will be sub-page accessed, domid is id of grantee domain, frame
     * is frame address of subpage grant, flags is grant type and flag
     * information, page_off is offset of the range of bytes, and length is
     * length of bytes to be accessed.
     */
    void (*update_subpage_entry)(grant_ref_t ref, domid_t domid,
                     unsigned long frame, int flags,
                     unsigned page_off, unsigned length);
    /*
     * Redirect an available grant entry on domain A to another grant
     * reference of domain B, then allow domain C to use grant reference
     * of domain B transitively. Ref parameter is an available grant entry
     * reference on domain A, domid is id of domain C which accesses grant
     * entry transitively, flags is grant type and flag information,
     * trans_domid is id of domain B whose grant entry is finally accessed
     * transitively, trans_gref is grant entry transitive reference of
     * domain B.
     */
    void (*update_trans_entry)(grant_ref_t ref, domid_t domid, int flags,
                   domid_t trans_domid, grant_ref_t trans_gref);
};

static struct gnttab_ops *gnttab_interface;

/*This reflects status of grant entries, so act as a global value*/
static grant_status_t *grstatus;

static int grant_table_version;

static struct gnttab_free_callback *gnttab_free_callback_list;

static int gnttab_expand(unsigned int req_entries);

#define RPP (PAGE_SIZE / sizeof(grant_ref_t))
#define SPP (PAGE_SIZE / sizeof(grant_status_t))

static inline grant_ref_t *__gnttab_entry(grant_ref_t entry)
{
    return &gnttab_list[(entry) / RPP][(entry) % RPP];
}
/* This can be used as an l-value */
#define gnttab_entry(entry) (*__gnttab_entry(entry))

static int get_free_entries(unsigned count)
{
    unsigned long flags;
    int ref, rc = 0;
    grant_ref_t head;

    spin_lock_irqsave(&gnttab_list_lock, flags);

    if ((gnttab_free_count < count) &&
        ((rc = gnttab_expand(count - gnttab_free_count)) < 0)) {
        spin_unlock_irqrestore(&gnttab_list_lock, flags);
        return rc;
    }

    ref = head = gnttab_free_head;
    gnttab_free_count -= count;
    while (count-- > 1)
        head = gnttab_entry(head);
    gnttab_free_head = gnttab_entry(head);
    gnttab_entry(head) = GNTTAB_LIST_END;

    spin_unlock_irqrestore(&gnttab_list_lock, flags);

    return ref;
}

static void do_free_callbacks(void)
{
    struct gnttab_free_callback *callback, *next;

    callback = gnttab_free_callback_list;
    gnttab_free_callback_list = NULL;

    while (callback != NULL) {
        next = callback->next;
        if (gnttab_free_count >= callback->count) {
            callback->next = NULL;
            callback->fn(callback->arg);
        } else {
            callback->next = gnttab_free_callback_list;
            gnttab_free_callback_list = callback;
        }
        callback = next;
    }
}

static inline void check_free_callbacks(void)
{
    if (unlikely(gnttab_free_callback_list))
        do_free_callbacks();
}

static void put_free_entry(grant_ref_t ref)
{
    unsigned long flags;
    spin_lock_irqsave(&gnttab_list_lock, flags);
    gnttab_entry(ref) = gnttab_free_head;
    gnttab_free_head = ref;
    gnttab_free_count++;
    check_free_callbacks();
    spin_unlock_irqrestore(&gnttab_list_lock, flags);
}

/*
 * Following applies to gnttab_update_entry_v1 and gnttab_update_entry_v2.
 * Introducing a valid entry into the grant table:
 *  1. Write ent->domid.
 *  2. Write ent->frame:
 *      GTF_permit_access:   Frame to which access is permitted.
 *      GTF_accept_transfer: Pseudo-phys frame slot being filled by new
 *                           frame, or zero if none.
 *  3. Write memory barrier (WMB).
 *  4. Write ent->flags, inc. valid type.
 */
static void gnttab_update_entry_v1(grant_ref_t ref, domid_t domid,
                   unsigned long frame, unsigned flags)
{
    gnttab_shared.v1[ref].domid = domid;
    gnttab_shared.v1[ref].frame = frame;
    wmb();
    gnttab_shared.v1[ref].flags = flags;
}

static void gnttab_update_entry_v2(grant_ref_t ref, domid_t domid,
                   unsigned long frame, unsigned flags)
{
    gnttab_shared.v2[ref].hdr.domid = domid;
    gnttab_shared.v2[ref].full_page.frame = frame;
    wmb();
    gnttab_shared.v2[ref].hdr.flags = GTF_permit_access | flags;
}

/*
 * Public grant-issuing interface functions
 */
void gnttab_grant_foreign_access_ref(grant_ref_t ref, domid_t domid,
                     unsigned long frame, int readonly)
{
    gnttab_interface->update_entry(ref, domid, frame,
               GTF_permit_access | (readonly ? GTF_readonly : 0));
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_ref);

int gnttab_grant_foreign_access(domid_t domid, unsigned long frame,
                int readonly)
{
    int ref;

    ref = get_free_entries(1);
    if (unlikely(ref < 0))
        return -ENOSPC;

    gnttab_grant_foreign_access_ref(ref, domid, frame, readonly);

    return ref;
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access);

static void gnttab_update_subpage_entry_v2(grant_ref_t ref, domid_t domid,
                       unsigned long frame, int flags,
                       unsigned page_off, unsigned length)
{
    gnttab_shared.v2[ref].sub_page.frame = frame;
    gnttab_shared.v2[ref].sub_page.page_off = page_off;
    gnttab_shared.v2[ref].sub_page.length = length;
    gnttab_shared.v2[ref].hdr.domid = domid;
    wmb();
    gnttab_shared.v2[ref].hdr.flags =
                GTF_permit_access | GTF_sub_page | flags;
}

int gnttab_grant_foreign_access_subpage_ref(grant_ref_t ref, domid_t domid,
                        unsigned long frame, int flags,
                        unsigned page_off,
                        unsigned length)
{
    if (flags & (GTF_accept_transfer | GTF_reading |
             GTF_writing | GTF_transitive))
        return -EPERM;

    if (gnttab_interface->update_subpage_entry == NULL)
        return -ENOSYS;

    gnttab_interface->update_subpage_entry(ref, domid, frame, flags,
                           page_off, length);

    return 0;
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_subpage_ref);

int gnttab_grant_foreign_access_subpage(domid_t domid, unsigned long frame,
                    int flags, unsigned page_off,
                    unsigned length)
{
    int ref, rc;

    ref = get_free_entries(1);
    if (unlikely(ref < 0))
        return -ENOSPC;

    rc = gnttab_grant_foreign_access_subpage_ref(ref, domid, frame, flags,
                             page_off, length);
    if (rc < 0) {
        put_free_entry(ref);
        return rc;
    }

    return ref;
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_subpage);

bool gnttab_subpage_grants_available(void)
{
    return gnttab_interface->update_subpage_entry != NULL;
}
EXPORT_SYMBOL_GPL(gnttab_subpage_grants_available);

static void gnttab_update_trans_entry_v2(grant_ref_t ref, domid_t domid,
                     int flags, domid_t trans_domid,
                     grant_ref_t trans_gref)
{
    gnttab_shared.v2[ref].transitive.trans_domid = trans_domid;
    gnttab_shared.v2[ref].transitive.gref = trans_gref;
    gnttab_shared.v2[ref].hdr.domid = domid;
    wmb();
    gnttab_shared.v2[ref].hdr.flags =
                GTF_permit_access | GTF_transitive | flags;
}

int gnttab_grant_foreign_access_trans_ref(grant_ref_t ref, domid_t domid,
                      int flags, domid_t trans_domid,
                      grant_ref_t trans_gref)
{
    if (flags & (GTF_accept_transfer | GTF_reading |
             GTF_writing | GTF_sub_page))
        return -EPERM;

    if (gnttab_interface->update_trans_entry == NULL)
        return -ENOSYS;

    gnttab_interface->update_trans_entry(ref, domid, flags, trans_domid,
                         trans_gref);

    return 0;
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_trans_ref);

int gnttab_grant_foreign_access_trans(domid_t domid, int flags,
                      domid_t trans_domid,
                      grant_ref_t trans_gref)
{
    int ref, rc;

    ref = get_free_entries(1);
    if (unlikely(ref < 0))
        return -ENOSPC;

    rc = gnttab_grant_foreign_access_trans_ref(ref, domid, flags,
                           trans_domid, trans_gref);
    if (rc < 0) {
        put_free_entry(ref);
        return rc;
    }

    return ref;
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_trans);

bool gnttab_trans_grants_available(void)
{
    return gnttab_interface->update_trans_entry != NULL;
}
EXPORT_SYMBOL_GPL(gnttab_trans_grants_available);

static int gnttab_query_foreign_access_v1(grant_ref_t ref)
{
    return gnttab_shared.v1[ref].flags & (GTF_reading|GTF_writing);
}

static int gnttab_query_foreign_access_v2(grant_ref_t ref)
{
    return grstatus[ref] & (GTF_reading|GTF_writing);
}

int gnttab_query_foreign_access(grant_ref_t ref)
{
    return gnttab_interface->query_foreign_access(ref);
}
EXPORT_SYMBOL_GPL(gnttab_query_foreign_access);

static int gnttab_end_foreign_access_ref_v1(grant_ref_t ref, int readonly)
{
    u16 flags, nflags;
    u16 *pflags;

    pflags = &gnttab_shared.v1[ref].flags;
    nflags = *pflags;
    do {
        flags = nflags;
        if (flags & (GTF_reading|GTF_writing))
            return 0;
    } while ((nflags = sync_cmpxchg(pflags, flags, 0)) != flags);

    return 1;
}

static int gnttab_end_foreign_access_ref_v2(grant_ref_t ref, int readonly)
{
    gnttab_shared.v2[ref].hdr.flags = 0;
    mb();
    if (grstatus[ref] & (GTF_reading|GTF_writing)) {
        return 0;
    } else {
        /* The read of grstatus needs to have acquire
        semantics.  On x86, reads already have
        that, and we just need to protect against
        compiler reorderings.  On other
        architectures we may need a full
        barrier. */
#ifdef CONFIG_X86
        barrier();
#else
        mb();
#endif
    }

    return 1;
}

static inline int _gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
{
    return gnttab_interface->end_foreign_access_ref(ref, readonly);
}

int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
{
    if (_gnttab_end_foreign_access_ref(ref, readonly))
        return 1;
    pr_warn("WARNING: g.e. %#x still in use!\n", ref);
    return 0;
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_access_ref);

struct deferred_entry {
    struct list_head list;
    grant_ref_t ref;
    bool ro;
    uint16_t warn_delay;
    struct page *page;
};
static LIST_HEAD(deferred_list);
static void gnttab_handle_deferred(unsigned long);
static DEFINE_TIMER(deferred_timer, gnttab_handle_deferred, 0, 0);

static void gnttab_handle_deferred(unsigned long unused)
{
    unsigned int nr = 10;
    struct deferred_entry *first = NULL;
    unsigned long flags;

    spin_lock_irqsave(&gnttab_list_lock, flags);
    while (nr--) {
        struct deferred_entry *entry
            = list_first_entry(&deferred_list,
                       struct deferred_entry, list);

        if (entry == first)
            break;
        list_del(&entry->list);
        spin_unlock_irqrestore(&gnttab_list_lock, flags);
        if (_gnttab_end_foreign_access_ref(entry->ref, entry->ro)) {
            put_free_entry(entry->ref);
            if (entry->page) {
                pr_debug("freeing g.e. %#x (pfn %#lx)\n",
                     entry->ref, page_to_pfn(entry->page));
                __free_page(entry->page);
            } else
                pr_info("freeing g.e. %#x\n", entry->ref);
            kfree(entry);
            entry = NULL;
        } else {
            if (!--entry->warn_delay)
                pr_info("g.e. %#x still pending\n",
                    entry->ref);
            if (!first)
                first = entry;
        }
        spin_lock_irqsave(&gnttab_list_lock, flags);
        if (entry)
            list_add_tail(&entry->list, &deferred_list);
        else if (list_empty(&deferred_list))
            break;
    }
    if (!list_empty(&deferred_list) && !timer_pending(&deferred_timer)) {
        deferred_timer.expires = jiffies + HZ;
        add_timer(&deferred_timer);
    }
    spin_unlock_irqrestore(&gnttab_list_lock, flags);
}

static void gnttab_add_deferred(grant_ref_t ref, bool readonly,
                struct page *page)
{
    struct deferred_entry *entry = kmalloc(sizeof(*entry), GFP_ATOMIC);
    const char *what = KERN_WARNING "leaking";

    if (entry) {
        unsigned long flags;

        entry->ref = ref;
        entry->ro = readonly;
        entry->page = page;
        entry->warn_delay = 60;
        spin_lock_irqsave(&gnttab_list_lock, flags);
        list_add_tail(&entry->list, &deferred_list);
        if (!timer_pending(&deferred_timer)) {
            deferred_timer.expires = jiffies + HZ;
            add_timer(&deferred_timer);
        }
        spin_unlock_irqrestore(&gnttab_list_lock, flags);
        what = KERN_DEBUG "deferring";
    }
    printk("%s g.e. %#x (pfn %#lx)\n",
           what, ref, page ? page_to_pfn(page) : -1);
}

void gnttab_end_foreign_access(grant_ref_t ref, int readonly,
                   unsigned long page)
{
    if (gnttab_end_foreign_access_ref(ref, readonly)) {
        put_free_entry(ref);
        if (page != 0)
            free_page(page);
    } else
        gnttab_add_deferred(ref, readonly,
                    page ? virt_to_page(page) : NULL);
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_access);

int gnttab_grant_foreign_transfer(domid_t domid, unsigned long pfn)
{
    int ref;

    ref = get_free_entries(1);
    if (unlikely(ref < 0))
        return -ENOSPC;
    gnttab_grant_foreign_transfer_ref(ref, domid, pfn);

    return ref;
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_transfer);

void gnttab_grant_foreign_transfer_ref(grant_ref_t ref, domid_t domid,
                       unsigned long pfn)
{
    gnttab_interface->update_entry(ref, domid, pfn, GTF_accept_transfer);
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_transfer_ref);

static unsigned long gnttab_end_foreign_transfer_ref_v1(grant_ref_t ref)
{
    unsigned long frame;
    u16           flags;
    u16          *pflags;

    pflags = &gnttab_shared.v1[ref].flags;

    /*
     * If a transfer is not even yet started, try to reclaim the grant
     * reference and return failure (== 0).
     */
    while (!((flags = *pflags) & GTF_transfer_committed)) {
        if (sync_cmpxchg(pflags, flags, 0) == flags)
            return 0;
        cpu_relax();
    }

    /* If a transfer is in progress then wait until it is completed. */
    while (!(flags & GTF_transfer_completed)) {
        flags = *pflags;
        cpu_relax();
    }

    rmb();  /* Read the frame number /after/ reading completion status. */
    frame = gnttab_shared.v1[ref].frame;
    BUG_ON(frame == 0);

    return frame;
}

static unsigned long gnttab_end_foreign_transfer_ref_v2(grant_ref_t ref)
{
    unsigned long frame;
    u16           flags;
    u16          *pflags;

    pflags = &gnttab_shared.v2[ref].hdr.flags;

    /*
     * If a transfer is not even yet started, try to reclaim the grant
     * reference and return failure (== 0).
     */
    while (!((flags = *pflags) & GTF_transfer_committed)) {
        if (sync_cmpxchg(pflags, flags, 0) == flags)
            return 0;
        cpu_relax();
    }

    /* If a transfer is in progress then wait until it is completed. */
    while (!(flags & GTF_transfer_completed)) {
        flags = *pflags;
        cpu_relax();
    }

    rmb();  /* Read the frame number /after/ reading completion status. */
    frame = gnttab_shared.v2[ref].full_page.frame;
    BUG_ON(frame == 0);

    return frame;
}

unsigned long gnttab_end_foreign_transfer_ref(grant_ref_t ref)
{
    return gnttab_interface->end_foreign_transfer_ref(ref);
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_transfer_ref);

unsigned long gnttab_end_foreign_transfer(grant_ref_t ref)
{
    unsigned long frame = gnttab_end_foreign_transfer_ref(ref);
    put_free_entry(ref);
    return frame;
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_transfer);

void gnttab_free_grant_reference(grant_ref_t ref)
{
    put_free_entry(ref);
}
EXPORT_SYMBOL_GPL(gnttab_free_grant_reference);

void gnttab_free_grant_references(grant_ref_t head)
{
    grant_ref_t ref;
    unsigned long flags;
    int count = 1;
    if (head == GNTTAB_LIST_END)
        return;
    spin_lock_irqsave(&gnttab_list_lock, flags);
    ref = head;
    while (gnttab_entry(ref) != GNTTAB_LIST_END) {
        ref = gnttab_entry(ref);
        count++;
    }
    gnttab_entry(ref) = gnttab_free_head;
    gnttab_free_head = head;
    gnttab_free_count += count;
    check_free_callbacks();
    spin_unlock_irqrestore(&gnttab_list_lock, flags);
}
EXPORT_SYMBOL_GPL(gnttab_free_grant_references);

int gnttab_alloc_grant_references(u16 count, grant_ref_t *head)
{
    int h = get_free_entries(count);

    if (h < 0)
        return -ENOSPC;

    *head = h;

    return 0;
}
EXPORT_SYMBOL_GPL(gnttab_alloc_grant_references);

int gnttab_empty_grant_references(const grant_ref_t *private_head)
{
    return (*private_head == GNTTAB_LIST_END);
}
EXPORT_SYMBOL_GPL(gnttab_empty_grant_references);

int gnttab_claim_grant_reference(grant_ref_t *private_head)
{
    grant_ref_t g = *private_head;
    if (unlikely(g == GNTTAB_LIST_END))
        return -ENOSPC;
    *private_head = gnttab_entry(g);
    return g;
}
EXPORT_SYMBOL_GPL(gnttab_claim_grant_reference);

void gnttab_release_grant_reference(grant_ref_t *private_head,
                    grant_ref_t release)
{
    gnttab_entry(release) = *private_head;
    *private_head = release;
}
EXPORT_SYMBOL_GPL(gnttab_release_grant_reference);

void gnttab_request_free_callback(struct gnttab_free_callback *callback,
                  void (*fn)(void *), void *arg, u16 count)
{
    unsigned long flags;
    spin_lock_irqsave(&gnttab_list_lock, flags);
    if (callback->next)
        goto out;
    callback->fn = fn;
    callback->arg = arg;
    callback->count = count;
    callback->next = gnttab_free_callback_list;
    gnttab_free_callback_list = callback;
    check_free_callbacks();
out:
    spin_unlock_irqrestore(&gnttab_list_lock, flags);
}
EXPORT_SYMBOL_GPL(gnttab_request_free_callback);

void gnttab_cancel_free_callback(struct gnttab_free_callback *callback)
{
    struct gnttab_free_callback **pcb;
    unsigned long flags;

    spin_lock_irqsave(&gnttab_list_lock, flags);
    for (pcb = &gnttab_free_callback_list; *pcb; pcb = &(*pcb)->next) {
        if (*pcb == callback) {
            *pcb = callback->next;
            break;
        }
    }
    spin_unlock_irqrestore(&gnttab_list_lock, flags);
}
EXPORT_SYMBOL_GPL(gnttab_cancel_free_callback);

static int grow_gnttab_list(unsigned int more_frames)
{
    unsigned int new_nr_grant_frames, extra_entries, i;
    unsigned int nr_glist_frames, new_nr_glist_frames;

    new_nr_grant_frames = nr_grant_frames + more_frames;
    extra_entries       = more_frames * GREFS_PER_GRANT_FRAME;

    nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
    new_nr_glist_frames =
        (new_nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
    for (i = nr_glist_frames; i < new_nr_glist_frames; i++) {
        gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_ATOMIC);
        if (!gnttab_list[i])
            goto grow_nomem;
    }


    for (i = GREFS_PER_GRANT_FRAME * nr_grant_frames;
         i < GREFS_PER_GRANT_FRAME * new_nr_grant_frames - 1; i++)
        gnttab_entry(i) = i + 1;

    gnttab_entry(i) = gnttab_free_head;
    gnttab_free_head = GREFS_PER_GRANT_FRAME * nr_grant_frames;
    gnttab_free_count += extra_entries;

    nr_grant_frames = new_nr_grant_frames;

    check_free_callbacks();

    return 0;

grow_nomem:
    for ( ; i >= nr_glist_frames; i--)
        free_page((unsigned long) gnttab_list[i]);
    return -ENOMEM;
}

static unsigned int __max_nr_grant_frames(void)
{
    struct gnttab_query_size query;
    int rc;

    query.dom = DOMID_SELF;

    rc = HYPERVISOR_grant_table_op(GNTTABOP_query_size, &query, 1);
    if ((rc < 0) || (query.status != GNTST_okay))
        return 4; /* Legacy max supported number of frames */

    return query.max_nr_frames;
}

unsigned int gnttab_max_grant_frames(void)
{
    unsigned int xen_max = __max_nr_grant_frames();

    if (xen_max > boot_max_nr_grant_frames)
        return boot_max_nr_grant_frames;
    return xen_max;
}
EXPORT_SYMBOL_GPL(gnttab_max_grant_frames);

/* Handling of paged out grant targets (GNTST_eagain) */
#define MAX_DELAY 256
static inline void
gnttab_retry_eagain_gop(unsigned int cmd, void *gop, int16_t *status,
                        const char *func)
{
    unsigned delay = 1;

    do {
        BUG_ON(HYPERVISOR_grant_table_op(cmd, gop, 1));
        if (*status == GNTST_eagain)
            msleep(delay++);
    } while ((*status == GNTST_eagain) && (delay < MAX_DELAY));

    if (delay >= MAX_DELAY) {
        printk(KERN_ERR "%s: %s eagain grant\n", func, current->comm);
        *status = GNTST_bad_page;
    }
}

void gnttab_batch_map(struct gnttab_map_grant_ref *batch, unsigned count)
{
    struct gnttab_map_grant_ref *op;

    if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, batch, count))
        BUG();
    for (op = batch; op < batch + count; op++)
        if (op->status == GNTST_eagain)
            gnttab_retry_eagain_gop(GNTTABOP_map_grant_ref, op,
                        &op->status, __func__);
}
EXPORT_SYMBOL_GPL(gnttab_batch_map);

void gnttab_batch_copy(struct gnttab_copy *batch, unsigned count)
{
    struct gnttab_copy *op;

    if (HYPERVISOR_grant_table_op(GNTTABOP_copy, batch, count))
        BUG();
    for (op = batch; op < batch + count; op++)
        if (op->status == GNTST_eagain)
            gnttab_retry_eagain_gop(GNTTABOP_copy, op,
                        &op->status, __func__);
}
EXPORT_SYMBOL_GPL(gnttab_batch_copy);

int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
            struct gnttab_map_grant_ref *kmap_ops,
            struct page **pages, unsigned int count)
{
    int i, ret;
    bool lazy = false;
    pte_t *pte;
    unsigned long mfn;

    ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map_ops, count);
    if (ret)
        return ret;

    /* Retry eagain maps */
    for (i = 0; i < count; i++)
        if (map_ops[i].status == GNTST_eagain)
            gnttab_retry_eagain_gop(GNTTABOP_map_grant_ref, map_ops + i,
                        &map_ops[i].status, __func__);

    if (xen_feature(XENFEAT_auto_translated_physmap))
        return ret;

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

    for (i = 0; i < count; i++) {
        /* 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);
        }
        ret = m2p_add_override(mfn, pages[i], kmap_ops ?
                       &kmap_ops[i] : NULL);
        if (ret)
            return ret;
    }

    if (lazy)
        arch_leave_lazy_mmu_mode();

    return ret;
}
EXPORT_SYMBOL_GPL(gnttab_map_refs);

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

    ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap_ops, count);
    if (ret)
        return ret;

    if (xen_feature(XENFEAT_auto_translated_physmap))
        return ret;

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

    for (i = 0; i < count; i++) {
        ret = m2p_remove_override(pages[i], kmap_ops ?
                       &kmap_ops[i] : NULL);
        if (ret)
            return ret;
    }

    if (lazy)
        arch_leave_lazy_mmu_mode();

    return ret;
}
EXPORT_SYMBOL_GPL(gnttab_unmap_refs);

static unsigned nr_status_frames(unsigned nr_grant_frames)
{
    return (nr_grant_frames * GREFS_PER_GRANT_FRAME + SPP - 1) / SPP;
}

static int gnttab_map_frames_v1(xen_pfn_t *frames, unsigned int nr_gframes)
{
    int rc;

    rc = arch_gnttab_map_shared(frames, nr_gframes,
                    gnttab_max_grant_frames(),
                    &gnttab_shared.addr);
    BUG_ON(rc);

    return 0;
}

static void gnttab_unmap_frames_v1(void)
{
    arch_gnttab_unmap(gnttab_shared.addr, nr_grant_frames);
}

static int gnttab_map_frames_v2(xen_pfn_t *frames, unsigned int nr_gframes)
{
    uint64_t *sframes;
    unsigned int nr_sframes;
    struct gnttab_get_status_frames getframes;
    int rc;

    nr_sframes = nr_status_frames(nr_gframes);

    /* No need for kzalloc as it is initialized in following hypercall
     * GNTTABOP_get_status_frames.
     */
    sframes = kmalloc(nr_sframes  * sizeof(uint64_t), GFP_ATOMIC);
    if (!sframes)
        return -ENOMEM;

    getframes.dom        = DOMID_SELF;
    getframes.nr_frames  = nr_sframes;
    set_xen_guest_handle(getframes.frame_list, sframes);

    rc = HYPERVISOR_grant_table_op(GNTTABOP_get_status_frames,
                       &getframes, 1);
    if (rc == -ENOSYS) {
        kfree(sframes);
        return -ENOSYS;
    }

    BUG_ON(rc || getframes.status);

    rc = arch_gnttab_map_status(sframes, nr_sframes,
                    nr_status_frames(gnttab_max_grant_frames()),
                    &grstatus);
    BUG_ON(rc);
    kfree(sframes);

    rc = arch_gnttab_map_shared(frames, nr_gframes,
                    gnttab_max_grant_frames(),
                    &gnttab_shared.addr);
    BUG_ON(rc);

    return 0;
}

static void gnttab_unmap_frames_v2(void)
{
    arch_gnttab_unmap(gnttab_shared.addr, nr_grant_frames);
    arch_gnttab_unmap(grstatus, nr_status_frames(nr_grant_frames));
}

static int gnttab_map(unsigned int start_idx, unsigned int end_idx)
{
    struct gnttab_setup_table setup;
    xen_pfn_t *frames;
    unsigned int nr_gframes = end_idx + 1;
    int rc;

    if (xen_hvm_domain()) {
        struct xen_add_to_physmap xatp;
        unsigned int i = end_idx;
        rc = 0;
        /*
         * Loop backwards, so that the first hypercall has the largest
         * index, ensuring that the table will grow only once.
         */
        do {
            xatp.domid = DOMID_SELF;
            xatp.idx = i;
            xatp.space = XENMAPSPACE_grant_table;
            xatp.gpfn = (xen_hvm_resume_frames >> PAGE_SHIFT) + i;
            rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp);
            if (rc != 0) {
                printk(KERN_WARNING
                        "grant table add_to_physmap failed, err=%d\n", rc);
                break;
            }
        } while (i-- > start_idx);

        return rc;
    }

    /* No need for kzalloc as it is initialized in following hypercall
     * GNTTABOP_setup_table.
     */
    frames = kmalloc(nr_gframes * sizeof(unsigned long), GFP_ATOMIC);
    if (!frames)
        return -ENOMEM;

    setup.dom        = DOMID_SELF;
    setup.nr_frames  = nr_gframes;
    set_xen_guest_handle(setup.frame_list, frames);

    rc = HYPERVISOR_grant_table_op(GNTTABOP_setup_table, &setup, 1);
    if (rc == -ENOSYS) {
        kfree(frames);
        return -ENOSYS;
    }

    BUG_ON(rc || setup.status);

    rc = gnttab_interface->map_frames(frames, nr_gframes);

    kfree(frames);

    return rc;
}

static struct gnttab_ops gnttab_v1_ops = {
    .map_frames         = gnttab_map_frames_v1,
    .unmap_frames           = gnttab_unmap_frames_v1,
    .update_entry           = gnttab_update_entry_v1,
    .end_foreign_access_ref     = gnttab_end_foreign_access_ref_v1,
    .end_foreign_transfer_ref   = gnttab_end_foreign_transfer_ref_v1,
    .query_foreign_access       = gnttab_query_foreign_access_v1,
};

static struct gnttab_ops gnttab_v2_ops = {
    .map_frames         = gnttab_map_frames_v2,
    .unmap_frames           = gnttab_unmap_frames_v2,
    .update_entry           = gnttab_update_entry_v2,
    .end_foreign_access_ref     = gnttab_end_foreign_access_ref_v2,
    .end_foreign_transfer_ref   = gnttab_end_foreign_transfer_ref_v2,
    .query_foreign_access       = gnttab_query_foreign_access_v2,
    .update_subpage_entry       = gnttab_update_subpage_entry_v2,
    .update_trans_entry     = gnttab_update_trans_entry_v2,
};

static void gnttab_request_version(void)
{
    int rc;
    struct gnttab_set_version gsv;

    if (xen_hvm_domain())
        gsv.version = 1;
    else
        gsv.version = 2;
    rc = HYPERVISOR_grant_table_op(GNTTABOP_set_version, &gsv, 1);
    if (rc == 0 && gsv.version == 2) {
        grant_table_version = 2;
        gnttab_interface = &gnttab_v2_ops;
    } else if (grant_table_version == 2) {
        /*
         * If we've already used version 2 features,
         * but then suddenly discover that they're not
         * available (e.g. migrating to an older
         * version of Xen), almost unbounded badness
         * can happen.
         */
        panic("we need grant tables version 2, but only version 1 is available");
    } else {
        grant_table_version = 1;
        gnttab_interface = &gnttab_v1_ops;
    }
    printk(KERN_INFO "Grant tables using version %d layout.\n",
        grant_table_version);
}

int gnttab_resume(void)
{
    unsigned int max_nr_gframes;

    gnttab_request_version();
    max_nr_gframes = gnttab_max_grant_frames();
    if (max_nr_gframes < nr_grant_frames)
        return -ENOSYS;

    if (xen_pv_domain())
        return gnttab_map(0, nr_grant_frames - 1);

    if (gnttab_shared.addr == NULL) {
        gnttab_shared.addr = ioremap(xen_hvm_resume_frames,
                        PAGE_SIZE * max_nr_gframes);
        if (gnttab_shared.addr == NULL) {
            printk(KERN_WARNING
                    "Failed to ioremap gnttab share frames!");
            return -ENOMEM;
        }
    }

    gnttab_map(0, nr_grant_frames - 1);

    return 0;
}

int gnttab_suspend(void)
{
    gnttab_interface->unmap_frames();
    return 0;
}

static int gnttab_expand(unsigned int req_entries)
{
    int rc;
    unsigned int cur, extra;

    cur = nr_grant_frames;
    extra = ((req_entries + (GREFS_PER_GRANT_FRAME-1)) /
         GREFS_PER_GRANT_FRAME);
    if (cur + extra > gnttab_max_grant_frames())
        return -ENOSPC;

    rc = gnttab_map(cur, cur + extra - 1);
    if (rc == 0)
        rc = grow_gnttab_list(extra);

    return rc;
}

int gnttab_init(void)
{
    int i;
    unsigned int max_nr_glist_frames, nr_glist_frames;
    unsigned int nr_init_grefs;
    int ret;

    nr_grant_frames = 1;
    boot_max_nr_grant_frames = __max_nr_grant_frames();

    /* Determine the maximum number of frames required for the
     * grant reference free list on the current hypervisor.
     */
    max_nr_glist_frames = (boot_max_nr_grant_frames *
                   GREFS_PER_GRANT_FRAME / RPP);

    gnttab_list = kmalloc(max_nr_glist_frames * sizeof(grant_ref_t *),
                  GFP_KERNEL);
    if (gnttab_list == NULL)
        return -ENOMEM;

    nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
    for (i = 0; i < nr_glist_frames; i++) {
        gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_KERNEL);
        if (gnttab_list[i] == NULL) {
            ret = -ENOMEM;
            goto ini_nomem;
        }
    }

    if (gnttab_resume() < 0) {
        ret = -ENODEV;
        goto ini_nomem;
    }

    nr_init_grefs = nr_grant_frames * GREFS_PER_GRANT_FRAME;

    for (i = NR_RESERVED_ENTRIES; i < nr_init_grefs - 1; i++)
        gnttab_entry(i) = i + 1;

    gnttab_entry(nr_init_grefs - 1) = GNTTAB_LIST_END;
    gnttab_free_count = nr_init_grefs - NR_RESERVED_ENTRIES;
    gnttab_free_head  = NR_RESERVED_ENTRIES;

    printk("Grant table initialized\n");
    return 0;

 ini_nomem:
    for (i--; i >= 0; i--)
        free_page((unsigned long)gnttab_list[i]);
    kfree(gnttab_list);
    return ret;
}
EXPORT_SYMBOL_GPL(gnttab_init);

static int __devinit __gnttab_init(void)
{
    /* Delay grant-table initialization in the PV on HVM case */
    if (xen_hvm_domain())
        return 0;

    if (!xen_pv_domain())
        return -ENODEV;

    return gnttab_init();
}

core_initcall(__gnttab_init);