/******************************************************************************
 * 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.
 */

#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt

#include <linux/memblock.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 <linux/workqueue.h>
#include <linux/ratelimit.h>
#include <linux/moduleparam.h>
#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
#include <linux/dma-mapping.h>
#endif

#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 <xen/swiotlb-xen.h>
#include <xen/balloon.h>
#ifdef CONFIG_X86
#include <asm/xen/cpuid.h>
#endif
#include <xen/mem-reservation.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/interface.h>

#include <asm/sync_bitops.h>

/* External tools reserve first few grant table entries. */
#define NR_RESERVED_ENTRIES 8
#define GNTTAB_LIST_END 0xffffffff

static grant_ref_t **gnttab_list;
static unsigned int nr_grant_frames;
static int gnttab_free_count;
static grant_ref_t gnttab_free_head;
static DEFINE_SPINLOCK(gnttab_list_lock);
struct grant_frames xen_auto_xlat_grant_frames;
static unsigned int xen_gnttab_version;
module_param_named(version, xen_gnttab_version, uint, 0);

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 {
        /*
         * Version of the grant interface.
         */
        unsigned int version;
        /*
         * Grant refs per grant frame.
         */
        unsigned int grefs_per_grant_frame;
        /*
         * 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);
};

struct unmap_refs_callback_data {
        struct completion completion;
        int result;
};

static const struct gnttab_ops *gnttab_interface;

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

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 int flags)
{
        gnttab_shared.v2[ref].hdr.domid = domid;
        gnttab_shared.v2[ref].full_page.frame = frame;
        wmb();  /* Hypervisor concurrent accesses. */
        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 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();   /* Concurrent access by hypervisor. */
        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(struct timer_list *);
static DEFINE_TIMER(deferred_timer, gnttab_handle_deferred);

static void gnttab_handle_deferred(struct timer_list *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));
                                put_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)
                        put_page(virt_to_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;
        struct gnttab_free_callback *cb;

        spin_lock_irqsave(&gnttab_list_lock, flags);

        /* Check if the callback is already on the list */
        cb = gnttab_free_callback_list;
        while (cb) {
                if (cb == callback)
                        goto out;
                cb = cb->next;
        }

        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 unsigned int gnttab_frames(unsigned int frames, unsigned int align)
{
        return (frames * gnttab_interface->grefs_per_grant_frame + align - 1) /
               align;
}

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;
        unsigned int grefs_per_frame;

        grefs_per_frame = gnttab_interface->grefs_per_grant_frame;

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

        nr_glist_frames = gnttab_frames(nr_grant_frames, RPP);
        new_nr_glist_frames = gnttab_frames(new_nr_grant_frames, 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_frame * nr_grant_frames;
             i < grefs_per_frame * new_nr_grant_frames - 1; i++)
                gnttab_entry(i) = i + 1;

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

        nr_grant_frames = new_nr_grant_frames;

        check_free_callbacks();

        return 0;

grow_nomem:
        while (i-- > nr_glist_frames)
                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();
        static unsigned int boot_max_nr_grant_frames;

        /* First time, initialize it properly. */
        if (!boot_max_nr_grant_frames)
                boot_max_nr_grant_frames = __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);

int gnttab_setup_auto_xlat_frames(phys_addr_t addr)
{
        xen_pfn_t *pfn;
        unsigned int max_nr_gframes = __max_nr_grant_frames();
        unsigned int i;
        void *vaddr;

        if (xen_auto_xlat_grant_frames.count)
                return -EINVAL;

        vaddr = xen_remap(addr, XEN_PAGE_SIZE * max_nr_gframes);
        if (vaddr == NULL) {
                pr_warn("Failed to ioremap gnttab share frames (addr=%pa)!\n",
                        &addr);
                return -ENOMEM;
        }
        pfn = kcalloc(max_nr_gframes, sizeof(pfn[0]), GFP_KERNEL);
        if (!pfn) {
                xen_unmap(vaddr);
                return -ENOMEM;
        }
        for (i = 0; i < max_nr_gframes; i++)
                pfn[i] = XEN_PFN_DOWN(addr) + i;

        xen_auto_xlat_grant_frames.vaddr = vaddr;
        xen_auto_xlat_grant_frames.pfn = pfn;
        xen_auto_xlat_grant_frames.count = max_nr_gframes;

        return 0;
}
EXPORT_SYMBOL_GPL(gnttab_setup_auto_xlat_frames);

void gnttab_free_auto_xlat_frames(void)
{
        if (!xen_auto_xlat_grant_frames.count)
                return;
        kfree(xen_auto_xlat_grant_frames.pfn);
        xen_unmap(xen_auto_xlat_grant_frames.vaddr);

        xen_auto_xlat_grant_frames.pfn = NULL;
        xen_auto_xlat_grant_frames.count = 0;
        xen_auto_xlat_grant_frames.vaddr = NULL;
}
EXPORT_SYMBOL_GPL(gnttab_free_auto_xlat_frames);

int gnttab_pages_set_private(int nr_pages, struct page **pages)
{
        int i;

        for (i = 0; i < nr_pages; i++) {
#if BITS_PER_LONG < 64
                struct xen_page_foreign *foreign;

                foreign = kzalloc(sizeof(*foreign), GFP_KERNEL);
                if (!foreign)
                        return -ENOMEM;

                set_page_private(pages[i], (unsigned long)foreign);
#endif
                SetPagePrivate(pages[i]);
        }

        return 0;
}
EXPORT_SYMBOL_GPL(gnttab_pages_set_private);

/**
 * gnttab_alloc_pages - alloc pages suitable for grant mapping into
 * @nr_pages: number of pages to alloc
 * @pages: returns the pages
 */
int gnttab_alloc_pages(int nr_pages, struct page **pages)
{
        int ret;

        ret = xen_alloc_unpopulated_pages(nr_pages, pages);
        if (ret < 0)
                return ret;

        ret = gnttab_pages_set_private(nr_pages, pages);
        if (ret < 0)
                gnttab_free_pages(nr_pages, pages);

        return ret;
}
EXPORT_SYMBOL_GPL(gnttab_alloc_pages);

#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
static inline void cache_init(struct gnttab_page_cache *cache)
{
        cache->pages = NULL;
}

static inline bool cache_empty(struct gnttab_page_cache *cache)
{
        return !cache->pages;
}

static inline struct page *cache_deq(struct gnttab_page_cache *cache)
{
        struct page *page;

        page = cache->pages;
        cache->pages = page->zone_device_data;

        return page;
}

static inline void cache_enq(struct gnttab_page_cache *cache, struct page *page)
{
        page->zone_device_data = cache->pages;
        cache->pages = page;
}
#else
static inline void cache_init(struct gnttab_page_cache *cache)
{
        INIT_LIST_HEAD(&cache->pages);
}

static inline bool cache_empty(struct gnttab_page_cache *cache)
{
        return list_empty(&cache->pages);
}

static inline struct page *cache_deq(struct gnttab_page_cache *cache)
{
        struct page *page;

        page = list_first_entry(&cache->pages, struct page, lru);
        list_del(&page->lru);

        return page;
}

static inline void cache_enq(struct gnttab_page_cache *cache, struct page *page)
{
        list_add(&page->lru, &cache->pages);
}
#endif

void gnttab_page_cache_init(struct gnttab_page_cache *cache)
{
        spin_lock_init(&cache->lock);
        cache_init(cache);
        cache->num_pages = 0;
}
EXPORT_SYMBOL_GPL(gnttab_page_cache_init);

int gnttab_page_cache_get(struct gnttab_page_cache *cache, struct page **page)
{
        unsigned long flags;

        spin_lock_irqsave(&cache->lock, flags);

        if (cache_empty(cache)) {
                spin_unlock_irqrestore(&cache->lock, flags);
                return gnttab_alloc_pages(1, page);
        }

        page[0] = cache_deq(cache);
        cache->num_pages--;

        spin_unlock_irqrestore(&cache->lock, flags);

        return 0;
}
EXPORT_SYMBOL_GPL(gnttab_page_cache_get);

void gnttab_page_cache_put(struct gnttab_page_cache *cache, struct page **page,
                           unsigned int num)
{
        unsigned long flags;
        unsigned int i;

        spin_lock_irqsave(&cache->lock, flags);

        for (i = 0; i < num; i++)
                cache_enq(cache, page[i]);
        cache->num_pages += num;

        spin_unlock_irqrestore(&cache->lock, flags);
}
EXPORT_SYMBOL_GPL(gnttab_page_cache_put);

void gnttab_page_cache_shrink(struct gnttab_page_cache *cache, unsigned int num)
{
        struct page *page[10];
        unsigned int i = 0;
        unsigned long flags;

        spin_lock_irqsave(&cache->lock, flags);

        while (cache->num_pages > num) {
                page[i] = cache_deq(cache);
                cache->num_pages--;
                if (++i == ARRAY_SIZE(page)) {
                        spin_unlock_irqrestore(&cache->lock, flags);
                        gnttab_free_pages(i, page);
                        i = 0;
                        spin_lock_irqsave(&cache->lock, flags);
                }
        }

        spin_unlock_irqrestore(&cache->lock, flags);

        if (i != 0)
                gnttab_free_pages(i, page);
}
EXPORT_SYMBOL_GPL(gnttab_page_cache_shrink);

void gnttab_pages_clear_private(int nr_pages, struct page **pages)
{
        int i;

        for (i = 0; i < nr_pages; i++) {
                if (PagePrivate(pages[i])) {
#if BITS_PER_LONG < 64
                        kfree((void *)page_private(pages[i]));
#endif
                        ClearPagePrivate(pages[i]);
                }
        }
}
EXPORT_SYMBOL_GPL(gnttab_pages_clear_private);

/**
 * gnttab_free_pages - free pages allocated by gnttab_alloc_pages()
 * @nr_pages; number of pages to free
 * @pages: the pages
 */
void gnttab_free_pages(int nr_pages, struct page **pages)
{
        gnttab_pages_clear_private(nr_pages, pages);
        xen_free_unpopulated_pages(nr_pages, pages);
}
EXPORT_SYMBOL_GPL(gnttab_free_pages);

#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
/**
 * gnttab_dma_alloc_pages - alloc DMAable pages suitable for grant mapping into
 * @args: arguments to the function
 */
int gnttab_dma_alloc_pages(struct gnttab_dma_alloc_args *args)
{
        unsigned long pfn, start_pfn;
        size_t size;
        int i, ret;

        size = args->nr_pages << PAGE_SHIFT;
        if (args->coherent)
                args->vaddr = dma_alloc_coherent(args->dev, size,
                                                 &args->dev_bus_addr,
                                                 GFP_KERNEL | __GFP_NOWARN);
        else
                args->vaddr = dma_alloc_wc(args->dev, size,
                                           &args->dev_bus_addr,
                                           GFP_KERNEL | __GFP_NOWARN);
        if (!args->vaddr) {
                pr_debug("Failed to allocate DMA buffer of size %zu\n", size);
                return -ENOMEM;
        }

        start_pfn = __phys_to_pfn(args->dev_bus_addr);
        for (pfn = start_pfn, i = 0; pfn < start_pfn + args->nr_pages;
                        pfn++, i++) {
                struct page *page = pfn_to_page(pfn);

                args->pages[i] = page;
                args->frames[i] = xen_page_to_gfn(page);
                xenmem_reservation_scrub_page(page);
        }

        xenmem_reservation_va_mapping_reset(args->nr_pages, args->pages);

        ret = xenmem_reservation_decrease(args->nr_pages, args->frames);
        if (ret != args->nr_pages) {
                pr_debug("Failed to decrease reservation for DMA buffer\n");
                ret = -EFAULT;
                goto fail;
        }

        ret = gnttab_pages_set_private(args->nr_pages, args->pages);
        if (ret < 0)
                goto fail;

        return 0;

fail:
        gnttab_dma_free_pages(args);
        return ret;
}
EXPORT_SYMBOL_GPL(gnttab_dma_alloc_pages);

/**
 * gnttab_dma_free_pages - free DMAable pages
 * @args: arguments to the function
 */
int gnttab_dma_free_pages(struct gnttab_dma_alloc_args *args)
{
        size_t size;
        int i, ret;

        gnttab_pages_clear_private(args->nr_pages, args->pages);

        for (i = 0; i < args->nr_pages; i++)
                args->frames[i] = page_to_xen_pfn(args->pages[i]);

        ret = xenmem_reservation_increase(args->nr_pages, args->frames);
        if (ret != args->nr_pages) {
                pr_debug("Failed to increase reservation for DMA buffer\n");
                ret = -EFAULT;
        } else {
                ret = 0;
        }

        xenmem_reservation_va_mapping_update(args->nr_pages, args->pages,
                                             args->frames);

        size = args->nr_pages << PAGE_SHIFT;
        if (args->coherent)
                dma_free_coherent(args->dev, size,
                                  args->vaddr, args->dev_bus_addr);
        else
                dma_free_wc(args->dev, size,
                            args->vaddr, args->dev_bus_addr);
        return ret;
}
EXPORT_SYMBOL_GPL(gnttab_dma_free_pages);
#endif

/* 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) {
                pr_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);

void gnttab_foreach_grant_in_range(struct page *page,
                                   unsigned int offset,
                                   unsigned int len,
                                   xen_grant_fn_t fn,
                                   void *data)
{
        unsigned int goffset;
        unsigned int glen;
        unsigned long xen_pfn;

        len = min_t(unsigned int, PAGE_SIZE - offset, len);
        goffset = xen_offset_in_page(offset);

        xen_pfn = page_to_xen_pfn(page) + XEN_PFN_DOWN(offset);

        while (len) {
                glen = min_t(unsigned int, XEN_PAGE_SIZE - goffset, len);
                fn(pfn_to_gfn(xen_pfn), goffset, glen, data);

                goffset = 0;
                xen_pfn++;
                len -= glen;
        }
}
EXPORT_SYMBOL_GPL(gnttab_foreach_grant_in_range);

void gnttab_foreach_grant(struct page **pages,
                          unsigned int nr_grefs,
                          xen_grant_fn_t fn,
                          void *data)
{
        unsigned int goffset = 0;
        unsigned long xen_pfn = 0;
        unsigned int i;

        for (i = 0; i < nr_grefs; i++) {
                if ((i % XEN_PFN_PER_PAGE) == 0) {
                        xen_pfn = page_to_xen_pfn(pages[i / XEN_PFN_PER_PAGE]);
                        goffset = 0;
                }

                fn(pfn_to_gfn(xen_pfn), goffset, XEN_PAGE_SIZE, data);

                goffset += XEN_PAGE_SIZE;
                xen_pfn++;
        }
}

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;

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

        for (i = 0; i < count; i++) {
                switch (map_ops[i].status) {
                case GNTST_okay:
                {
                        struct xen_page_foreign *foreign;

                        SetPageForeign(pages[i]);
                        foreign = xen_page_foreign(pages[i]);
                        foreign->domid = map_ops[i].dom;
                        foreign->gref = map_ops[i].ref;
                        break;
                }

                case GNTST_no_device_space:
                        pr_warn_ratelimited("maptrack limit reached, can't map all guest pages\n");
                        break;

                case GNTST_eagain:
                        /* Retry eagain maps */
                        gnttab_retry_eagain_gop(GNTTABOP_map_grant_ref,
                                                map_ops + i,
                                                &map_ops[i].status, __func__);
                        /* Test status in next loop iteration. */
                        i--;
                        break;

                default:
                        break;
                }
        }

        return set_foreign_p2m_mapping(map_ops, kmap_ops, pages, count);
}
EXPORT_SYMBOL_GPL(gnttab_map_refs);

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

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

        for (i = 0; i < count; i++)
                ClearPageForeign(pages[i]);

        return clear_foreign_p2m_mapping(unmap_ops, kunmap_ops, pages, count);
}
EXPORT_SYMBOL_GPL(gnttab_unmap_refs);

#define GNTTAB_UNMAP_REFS_DELAY 5

static void __gnttab_unmap_refs_async(struct gntab_unmap_queue_data* item);

static void gnttab_unmap_work(struct work_struct *work)
{
        struct gntab_unmap_queue_data
                *unmap_data = container_of(work, 
                                           struct gntab_unmap_queue_data,
                                           gnttab_work.work);
        if (unmap_data->age != UINT_MAX)
                unmap_data->age++;
        __gnttab_unmap_refs_async(unmap_data);
}

static void __gnttab_unmap_refs_async(struct gntab_unmap_queue_data* item)
{
        int ret;
        int pc;

        for (pc = 0; pc < item->count; pc++) {
                if (page_count(item->pages[pc]) > 1) {
                        unsigned long delay = GNTTAB_UNMAP_REFS_DELAY * (item->age + 1);
                        schedule_delayed_work(&item->gnttab_work,
                                              msecs_to_jiffies(delay));
                        return;
                }
        }

        ret = gnttab_unmap_refs(item->unmap_ops, item->kunmap_ops,
                                item->pages, item->count);
        item->done(ret, item);
}

void gnttab_unmap_refs_async(struct gntab_unmap_queue_data* item)
{
        INIT_DELAYED_WORK(&item->gnttab_work, gnttab_unmap_work);
        item->age = 0;

        __gnttab_unmap_refs_async(item);
}
EXPORT_SYMBOL_GPL(gnttab_unmap_refs_async);

static void unmap_refs_callback(int result,
                struct gntab_unmap_queue_data *data)
{
        struct unmap_refs_callback_data *d = data->data;

        d->result = result;
        complete(&d->completion);
}

int gnttab_unmap_refs_sync(struct gntab_unmap_queue_data *item)
{
        struct unmap_refs_callback_data data;

        init_completion(&data.completion);
        item->data = &data;
        item->done = &unmap_refs_callback;
        gnttab_unmap_refs_async(item);
        wait_for_completion(&data.completion);

        return data.result;
}
EXPORT_SYMBOL_GPL(gnttab_unmap_refs_sync);

static unsigned int nr_status_frames(unsigned int nr_grant_frames)
{
        return gnttab_frames(nr_grant_frames, 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_array(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_feature(XENFEAT_auto_translated_physmap)) {
                struct xen_add_to_physmap xatp;
                unsigned int i = end_idx;
                rc = 0;
                BUG_ON(xen_auto_xlat_grant_frames.count < nr_gframes);
                /*
                 * 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_auto_xlat_grant_frames.pfn[i];
                        rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp);
                        if (rc != 0) {
                                pr_warn("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_array(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 const struct gnttab_ops gnttab_v1_ops = {
        .version                        = 1,
        .grefs_per_grant_frame          = XEN_PAGE_SIZE /
                                          sizeof(struct grant_entry_v1),
        .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 const struct gnttab_ops gnttab_v2_ops = {
        .version                        = 2,
        .grefs_per_grant_frame          = XEN_PAGE_SIZE /
                                          sizeof(union grant_entry_v2),
        .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,
};

static bool gnttab_need_v2(void)
{
#ifdef CONFIG_X86
        uint32_t base, width;

        if (xen_pv_domain()) {
                base = xen_cpuid_base();
                if (cpuid_eax(base) < 5)
                        return false;   /* Information not available, use V1. */
                width = cpuid_ebx(base + 5) &
                        XEN_CPUID_MACHINE_ADDRESS_WIDTH_MASK;
                return width > 32 + PAGE_SHIFT;
        }
#endif
        return !!(max_possible_pfn >> 32);
}

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

        if (gnttab_need_v2())
                gsv.version = 2;
        else
                gsv.version = 1;

        /* Boot parameter overrides automatic selection. */
        if (xen_gnttab_version >= 1 && xen_gnttab_version <= 2)
                gsv.version = xen_gnttab_version;

        rc = HYPERVISOR_grant_table_op(GNTTABOP_set_version, &gsv, 1);
        if (rc == 0 && gsv.version == 2)
                gnttab_interface = &gnttab_v2_ops;
        else
                gnttab_interface = &gnttab_v1_ops;
        pr_info("Grant tables using version %d layout\n",
                gnttab_interface->version);
}

static int gnttab_setup(void)
{
        unsigned int max_nr_gframes;

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

        if (xen_feature(XENFEAT_auto_translated_physmap) && gnttab_shared.addr == NULL) {
                gnttab_shared.addr = xen_auto_xlat_grant_frames.vaddr;
                if (gnttab_shared.addr == NULL) {
                        pr_warn("gnttab share frames is not mapped!\n");
                        return -ENOMEM;
                }
        }
        return gnttab_map(0, nr_grant_frames - 1);
}

int gnttab_resume(void)
{
        gnttab_request_version();
        return gnttab_setup();
}

int gnttab_suspend(void)
{
        if (!xen_feature(XENFEAT_auto_translated_physmap))
                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 + gnttab_interface->grefs_per_grant_frame - 1) /
                 gnttab_interface->grefs_per_grant_frame);
        if (cur + extra > gnttab_max_grant_frames()) {
                pr_warn_ratelimited("xen/grant-table: max_grant_frames reached"
                                    " cur=%u extra=%u limit=%u"
                                    " gnttab_free_count=%u req_entries=%u\n",
                                    cur, extra, gnttab_max_grant_frames(),
                                    gnttab_free_count, req_entries);
                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 long max_nr_grant_frames;
        unsigned int max_nr_glist_frames, nr_glist_frames;
        unsigned int nr_init_grefs;
        int ret;

        gnttab_request_version();
        max_nr_grant_frames = gnttab_max_grant_frames();
        nr_grant_frames = 1;

        /* Determine the maximum number of frames required for the
         * grant reference free list on the current hypervisor.
         */
        max_nr_glist_frames = (max_nr_grant_frames *
                               gnttab_interface->grefs_per_grant_frame / RPP);

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

        nr_glist_frames = gnttab_frames(nr_grant_frames, 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;
                }
        }

        ret = arch_gnttab_init(max_nr_grant_frames,
                               nr_status_frames(max_nr_grant_frames));
        if (ret < 0)
                goto ini_nomem;

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

        nr_init_grefs = nr_grant_frames *
                        gnttab_interface->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 __gnttab_init(void)
{
        if (!xen_domain())
                return -ENODEV;

        /* Delay grant-table initialization in the PV on HVM case */
        if (xen_hvm_domain() && !xen_pvh_domain())
                return 0;

        return gnttab_init();
}
/* Starts after core_initcall so that xen_pvh_gnttab_setup can be called
 * beforehand to initialize xen_auto_xlat_grant_frames. */
core_initcall_sync(__gnttab_init);