Merge tag 'writeback-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg...

[mirror_ubuntu-artful-kernel.git] / drivers / xen / grant-table.c

/******************************************************************************
 * 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/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

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 int grefs_per_grant_frame;

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;
        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 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;

        BUG_ON(grefs_per_grant_frame == 0);

        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) {
                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);

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)
{
        BUG_ON(grefs_per_grant_frame == 0);
        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) {
                                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(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;
                grefs_per_grant_frame = PAGE_SIZE / sizeof(union grant_entry_v2);
                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;
                grefs_per_grant_frame = PAGE_SIZE / sizeof(struct grant_entry_v1);
                gnttab_interface = &gnttab_v1_ops;
        }
        pr_info("Grant tables using version %d layout\n", grant_table_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_pv_domain())
                return gnttab_map(0, nr_grant_frames - 1);

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

        gnttab_map(0, nr_grant_frames - 1);

        return 0;
}

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

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

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

        BUG_ON(grefs_per_grant_frame == 0);
        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;

        gnttab_request_version();
        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.
         */
        BUG_ON(grefs_per_grant_frame == 0);
        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_setup() < 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 __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);