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

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>

#include <xen/interface/xen.h>
#include <xen/page.h>
#include <xen/grant_table.h>
#include <asm/xen/hypercall.h>

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


/* External tools reserve first few grant table entries. */
#define NR_RESERVED_ENTRIES 8
#define GNTTAB_LIST_END 0xffffffff
#define GREFS_PER_GRANT_FRAME (PAGE_SIZE / sizeof(struct grant_entry))

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);

static struct grant_entry *shared;

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))

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;
        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);
}

static void update_grant_entry(grant_ref_t ref, domid_t domid,
                               unsigned long frame, unsigned flags)
{
        /*
         * 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.
         */
        shared[ref].frame = frame;
        shared[ref].domid = domid;
        wmb();
        shared[ref].flags = flags;
}

/*
 * Public grant-issuing interface functions
 */
void gnttab_grant_foreign_access_ref(grant_ref_t ref, domid_t domid,
                                     unsigned long frame, int readonly)
{
        update_grant_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);

int gnttab_query_foreign_access(grant_ref_t ref)
{
        u16 nflags;

        nflags = shared[ref].flags;

        return (nflags & (GTF_reading|GTF_writing));
}
EXPORT_SYMBOL_GPL(gnttab_query_foreign_access);

int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
{
        u16 flags, nflags;

        nflags = shared[ref].flags;
        do {
                flags = nflags;
                if (flags & (GTF_reading|GTF_writing)) {
                        printk(KERN_ALERT "WARNING: g.e. still in use!\n");
                        return 0;
                }
        } while ((nflags = sync_cmpxchg(&shared[ref].flags, flags, 0)) != flags);

        return 1;
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_access_ref);

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 {
                /* XXX This needs to be fixed so that the ref and page are
                   placed on a list to be freed up later. */
                printk(KERN_WARNING
                       "WARNING: leaking g.e. and page still in use!\n");
        }
}
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)
{
        update_grant_entry(ref, domid, pfn, GTF_accept_transfer);
}
EXPORT_SYMBOL_GPL(gnttab_grant_foreign_transfer_ref);

unsigned long gnttab_end_foreign_transfer_ref(grant_ref_t ref)
{
        unsigned long frame;
        u16           flags;

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

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

        return frame;
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_transfer_ref);

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

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

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

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

        if (h < 0)
                return -ENOSPC;

        *head = h;

        return 0;
}
EXPORT_SYMBOL_GPL(gnttab_alloc_grant_references);

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

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

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

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

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

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

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

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

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


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

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

        nr_grant_frames = new_nr_grant_frames;

        check_free_callbacks();

        return 0;

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

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

        query.dom = DOMID_SELF;

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

        return query.max_nr_frames;
}

static inline unsigned int max_nr_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;
}

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

        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 = arch_gnttab_map_shared(frames, nr_gframes, max_nr_grant_frames(),
                                    &shared);
        BUG_ON(rc);

        kfree(frames);

        return 0;
}

int gnttab_resume(void)
{
        if (max_nr_grant_frames() < nr_grant_frames)
                return -ENOSYS;
        return gnttab_map(0, nr_grant_frames - 1);
}

int gnttab_suspend(void)
{
        arch_gnttab_unmap_shared(shared, nr_grant_frames);
        return 0;
}

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

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

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

        return rc;
}

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

        if (!xen_domain())
                return -ENODEV;

        nr_grant_frames = 1;
        boot_max_nr_grant_frames = __max_nr_grant_frames();

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

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

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

        if (gnttab_resume() < 0)
                return -ENODEV;

        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 -ENOMEM;
}

core_initcall(gnttab_init);