/******************************************************************************
   * gntalloc.c
   *
   * Device for creating grant references (in user-space) that may be shared
   * with other domains.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   */
  
  /*
   * This driver exists to allow userspace programs in Linux to allocate kernel
   * memory that will later be shared with another domain.  Without this device,
   * Linux userspace programs cannot create grant references.
   *
   * How this stuff works:
   *   X -> granting a page to Y
   *   Y -> mapping the grant from X
   *
   *   1. X uses the gntalloc device to allocate a page of kernel memory, P.
   *   2. X creates an entry in the grant table that says domid(Y) can access P.
   *      This is done without a hypercall unless the grant table needs expansion.
   *   3. X gives the grant reference identifier, GREF, to Y.
   *   4. Y maps the page, either directly into kernel memory for use in a backend
   *      driver, or via a the gntdev device to map into the address space of an
   *      application running in Y. This is the first point at which Xen does any
   *      tracking of the page.
   *   5. A program in X mmap()s a segment of the gntalloc device that corresponds
   *      to the shared page, and can now communicate with Y over the shared page.
   *
   *
   * NOTE TO USERSPACE LIBRARIES:
   *   The grant allocation and mmap()ing are, naturally, two separate operations.
   *   You set up the sharing by calling the create ioctl() and then the mmap().
   *   Teardown requires munmap() and either close() or ioctl().
   *
   * WARNING: Since Xen does not allow a guest to forcibly end the use of a grant
   * reference, this device can be used to consume kernel memory by leaving grant
   * references mapped by another domain when an application exits. Therefore,
   * there is a global limit on the number of pages that can be allocated. When
   * all references to the page are unmapped, it will be freed during the next
   * grant operation.
   */

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

  #include <linux/atomic.h>
  #include <linux/module.h>
  #include <linux/miscdevice.h>
  #include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/slab.h>
  #include <linux/fs.h>
  #include <linux/device.h>
  #include <linux/mm.h>
  #include <linux/uaccess.h>
  #include <linux/types.h>
  #include <linux/list.h>

  #include <linux/highmem.h>

  
  #include <xen/xen.h>
  #include <xen/page.h>
  #include <xen/grant_table.h>
  #include <xen/gntalloc.h>

  #include <xen/events.h>

  
  static int limit = 1024;
  module_param(limit, int, 0644);
  MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
  		"the gntalloc device");
  
  static LIST_HEAD(gref_list);

  static DEFINE_MUTEX(gref_mutex);

  static int gref_size;

  struct notify_info {
  	uint16_t pgoff:12;    /* Bits 0-11: Offset of the byte to clear */
  	uint16_t flags:2;     /* Bits 12-13: Unmap notification flags */
  	int event;            /* Port (event channel) to notify */
  };

  /* Metadata on a grant reference. */
  struct gntalloc_gref {
  	struct list_head next_gref;  /* list entry gref_list */
  	struct list_head next_file;  /* list entry file->list, if open */
  	struct page *page;	     /* The shared page */
  	uint64_t file_index;         /* File offset for mmap() */
  	unsigned int users;          /* Use count - when zero, waiting on Xen */
  	grant_ref_t gref_id;         /* The grant reference number */

  	struct notify_info notify;   /* Unmap notification */

  };
  
  struct gntalloc_file_private_data {
  	struct list_head list;
  	uint64_t index;
  };

  struct gntalloc_vma_private_data {
  	struct gntalloc_gref *gref;
  	int users;
  	int count;
  };

  static void __del_gref(struct gntalloc_gref *gref);
  
  static void do_cleanup(void)
  {
  	struct gntalloc_gref *gref, *n;
  	list_for_each_entry_safe(gref, n, &gref_list, next_gref) {
  		if (!gref->users)
  			__del_gref(gref);
  	}
  }
  
  static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
  	uint32_t *gref_ids, struct gntalloc_file_private_data *priv)
  {
  	int i, rc, readonly;
  	LIST_HEAD(queue_gref);
  	LIST_HEAD(queue_file);

  	struct gntalloc_gref *gref, *next;

  
  	readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
  	rc = -ENOMEM;
  	for (i = 0; i < op->count; i++) {
  		gref = kzalloc(sizeof(*gref), GFP_KERNEL);
  		if (!gref)
  			goto undo;
  		list_add_tail(&gref->next_gref, &queue_gref);
  		list_add_tail(&gref->next_file, &queue_file);
  		gref->users = 1;
  		gref->file_index = op->index + i * PAGE_SIZE;
  		gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
  		if (!gref->page)
  			goto undo;
  
  		/* Grant foreign access to the page. */

  		rc = gnttab_grant_foreign_access(op->domid,

  			pfn_to_mfn(page_to_pfn(gref->page)), readonly);

  		if (rc < 0)

  			goto undo;

  		gref_ids[i] = gref->gref_id = rc;

  	}
  
  	/* Add to gref lists. */

  	mutex_lock(&gref_mutex);

  	list_splice_tail(&queue_gref, &gref_list);
  	list_splice_tail(&queue_file, &priv->list);

  	mutex_unlock(&gref_mutex);

  
  	return 0;
  
  undo:

  	mutex_lock(&gref_mutex);

  	gref_size -= (op->count - i);

  	list_for_each_entry_safe(gref, next, &queue_file, next_file) {
  		list_del(&gref->next_file);

  		__del_gref(gref);
  	}
  
  	/* It's possible for the target domain to map the just-allocated grant
  	 * references by blindly guessing their IDs; if this is done, then
  	 * __del_gref will leave them in the queue_gref list. They need to be
  	 * added to the global list so that we can free them when they are no
  	 * longer referenced.
  	 */
  	if (unlikely(!list_empty(&queue_gref)))
  		list_splice_tail(&queue_gref, &gref_list);

  	mutex_unlock(&gref_mutex);

  	return rc;
  }
  
  static void __del_gref(struct gntalloc_gref *gref)
  {

  	if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
  		uint8_t *tmp = kmap(gref->page);
  		tmp[gref->notify.pgoff] = 0;
  		kunmap(gref->page);
  	}

  	if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {

  		notify_remote_via_evtchn(gref->notify.event);

  		evtchn_put(gref->notify.event);
  	}

  
  	gref->notify.flags = 0;

  	if (gref->gref_id) {

  		if (gnttab_query_foreign_access(gref->gref_id))
  			return;
  
  		if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
  			return;

  
  		gnttab_free_grant_reference(gref->gref_id);

  	}
  
  	gref_size--;
  	list_del(&gref->next_gref);
  
  	if (gref->page)
  		__free_page(gref->page);
  
  	kfree(gref);
  }
  
  /* finds contiguous grant references in a file, returns the first */
  static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,
  		uint64_t index, uint32_t count)
  {
  	struct gntalloc_gref *rv = NULL, *gref;
  	list_for_each_entry(gref, &priv->list, next_file) {
  		if (gref->file_index == index && !rv)
  			rv = gref;
  		if (rv) {
  			if (gref->file_index != index)
  				return NULL;
  			index += PAGE_SIZE;
  			count--;
  			if (count == 0)
  				return rv;
  		}
  	}
  	return NULL;
  }
  
  /*
   * -------------------------------------
   *  File operations.
   * -------------------------------------
   */
  static int gntalloc_open(struct inode *inode, struct file *filp)
  {
  	struct gntalloc_file_private_data *priv;
  
  	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
  	if (!priv)
  		goto out_nomem;
  	INIT_LIST_HEAD(&priv->list);
  
  	filp->private_data = priv;
  
  	pr_debug("%s: priv %p
  ", __func__, priv);
  
  	return 0;
  
  out_nomem:
  	return -ENOMEM;
  }
  
  static int gntalloc_release(struct inode *inode, struct file *filp)
  {
  	struct gntalloc_file_private_data *priv = filp->private_data;
  	struct gntalloc_gref *gref;
  
  	pr_debug("%s: priv %p
  ", __func__, priv);

  	mutex_lock(&gref_mutex);

  	while (!list_empty(&priv->list)) {
  		gref = list_entry(priv->list.next,
  			struct gntalloc_gref, next_file);
  		list_del(&gref->next_file);
  		gref->users--;
  		if (gref->users == 0)
  			__del_gref(gref);
  	}
  	kfree(priv);

  	mutex_unlock(&gref_mutex);

  
  	return 0;
  }
  
  static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
  		struct ioctl_gntalloc_alloc_gref __user *arg)
  {
  	int rc = 0;
  	struct ioctl_gntalloc_alloc_gref op;
  	uint32_t *gref_ids;
  
  	pr_debug("%s: priv %p
  ", __func__, priv);
  
  	if (copy_from_user(&op, arg, sizeof(op))) {
  		rc = -EFAULT;
  		goto out;
  	}

  	gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_TEMPORARY);

  	if (!gref_ids) {
  		rc = -ENOMEM;
  		goto out;
  	}

  	mutex_lock(&gref_mutex);

  	/* Clean up pages that were at zero (local) users but were still mapped
  	 * by remote domains. Since those pages count towards the limit that we
  	 * are about to enforce, removing them here is a good idea.
  	 */
  	do_cleanup();
  	if (gref_size + op.count > limit) {

  		mutex_unlock(&gref_mutex);

  		rc = -ENOSPC;
  		goto out_free;
  	}
  	gref_size += op.count;
  	op.index = priv->index;
  	priv->index += op.count * PAGE_SIZE;

  	mutex_unlock(&gref_mutex);

  
  	rc = add_grefs(&op, gref_ids, priv);
  	if (rc < 0)
  		goto out_free;
  
  	/* Once we finish add_grefs, it is unsafe to touch the new reference,
  	 * since it is possible for a concurrent ioctl to remove it (by guessing
  	 * its index). If the userspace application doesn't provide valid memory
  	 * to write the IDs to, then it will need to close the file in order to
  	 * release - which it will do by segfaulting when it tries to access the
  	 * IDs to close them.
  	 */
  	if (copy_to_user(arg, &op, sizeof(op))) {
  		rc = -EFAULT;
  		goto out_free;
  	}
  	if (copy_to_user(arg->gref_ids, gref_ids,
  			sizeof(gref_ids[0]) * op.count)) {
  		rc = -EFAULT;
  		goto out_free;
  	}
  
  out_free:
  	kfree(gref_ids);
  out:
  	return rc;
  }
  
  static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
  		void __user *arg)
  {
  	int i, rc = 0;
  	struct ioctl_gntalloc_dealloc_gref op;
  	struct gntalloc_gref *gref, *n;
  
  	pr_debug("%s: priv %p
  ", __func__, priv);
  
  	if (copy_from_user(&op, arg, sizeof(op))) {
  		rc = -EFAULT;
  		goto dealloc_grant_out;
  	}

  	mutex_lock(&gref_mutex);

  	gref = find_grefs(priv, op.index, op.count);
  	if (gref) {
  		/* Remove from the file list only, and decrease reference count.
  		 * The later call to do_cleanup() will remove from gref_list and
  		 * free the memory if the pages aren't mapped anywhere.
  		 */
  		for (i = 0; i < op.count; i++) {
  			n = list_entry(gref->next_file.next,
  				struct gntalloc_gref, next_file);
  			list_del(&gref->next_file);
  			gref->users--;
  			gref = n;
  		}
  	} else {
  		rc = -EINVAL;
  	}
  
  	do_cleanup();

  	mutex_unlock(&gref_mutex);

  dealloc_grant_out:
  	return rc;
  }

  static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv,
  		void __user *arg)
  {
  	struct ioctl_gntalloc_unmap_notify op;
  	struct gntalloc_gref *gref;
  	uint64_t index;
  	int pgoff;
  	int rc;
  
  	if (copy_from_user(&op, arg, sizeof(op)))
  		return -EFAULT;
  
  	index = op.index & ~(PAGE_SIZE - 1);
  	pgoff = op.index & (PAGE_SIZE - 1);

  	mutex_lock(&gref_mutex);

  
  	gref = find_grefs(priv, index, 1);
  	if (!gref) {
  		rc = -ENOENT;
  		goto unlock_out;
  	}
  
  	if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) {
  		rc = -EINVAL;
  		goto unlock_out;
  	}

  	/* We need to grab a reference to the event channel we are going to use
  	 * to send the notify before releasing the reference we may already have
  	 * (if someone has called this ioctl twice). This is required so that
  	 * it is possible to change the clear_byte part of the notification
  	 * without disturbing the event channel part, which may now be the last
  	 * reference to that event channel.
  	 */
  	if (op.action & UNMAP_NOTIFY_SEND_EVENT) {
  		if (evtchn_get(op.event_channel_port)) {
  			rc = -EINVAL;
  			goto unlock_out;
  		}
  	}
  
  	if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT)
  		evtchn_put(gref->notify.event);

  	gref->notify.flags = op.action;
  	gref->notify.pgoff = pgoff;
  	gref->notify.event = op.event_channel_port;
  	rc = 0;

   unlock_out:

  	mutex_unlock(&gref_mutex);

  	return rc;
  }

  static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
  		unsigned long arg)
  {
  	struct gntalloc_file_private_data *priv = filp->private_data;
  
  	switch (cmd) {
  	case IOCTL_GNTALLOC_ALLOC_GREF:
  		return gntalloc_ioctl_alloc(priv, (void __user *)arg);
  
  	case IOCTL_GNTALLOC_DEALLOC_GREF:
  		return gntalloc_ioctl_dealloc(priv, (void __user *)arg);

  	case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY:
  		return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);

  	default:
  		return -ENOIOCTLCMD;
  	}
  
  	return 0;
  }

  static void gntalloc_vma_open(struct vm_area_struct *vma)
  {

  	struct gntalloc_vma_private_data *priv = vma->vm_private_data;
  
  	if (!priv)

  		return;

  	mutex_lock(&gref_mutex);

  	priv->users++;

  	mutex_unlock(&gref_mutex);

  }

  static void gntalloc_vma_close(struct vm_area_struct *vma)
  {

  	struct gntalloc_vma_private_data *priv = vma->vm_private_data;
  	struct gntalloc_gref *gref, *next;
  	int i;
  
  	if (!priv)

  		return;

  	mutex_lock(&gref_mutex);

  	priv->users--;
  	if (priv->users == 0) {
  		gref = priv->gref;
  		for (i = 0; i < priv->count; i++) {
  			gref->users--;
  			next = list_entry(gref->next_gref.next,
  					  struct gntalloc_gref, next_gref);
  			if (gref->users == 0)
  				__del_gref(gref);
  			gref = next;
  		}
  		kfree(priv);
  	}

  	mutex_unlock(&gref_mutex);

  }
  
  static struct vm_operations_struct gntalloc_vmops = {

  	.open = gntalloc_vma_open,

  	.close = gntalloc_vma_close,
  };
  
  static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
  {
  	struct gntalloc_file_private_data *priv = filp->private_data;

  	struct gntalloc_vma_private_data *vm_priv;

  	struct gntalloc_gref *gref;
  	int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
  	int rv, i;

  	if (!(vma->vm_flags & VM_SHARED)) {

  		pr_err("%s: Mapping must be shared
  ", __func__);

  		return -EINVAL;
  	}

  	vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL);
  	if (!vm_priv)
  		return -ENOMEM;

  	mutex_lock(&gref_mutex);

  
  	pr_debug("%s: priv %p,%p, page %lu+%d
  ", __func__,
  		       priv, vm_priv, vma->vm_pgoff, count);

  	gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
  	if (gref == NULL) {
  		rv = -ENOENT;
  		pr_debug("%s: Could not find grant reference",
  				__func__);

  		kfree(vm_priv);

  		goto out_unlock;
  	}

  	vm_priv->gref = gref;
  	vm_priv->users = 1;
  	vm_priv->count = count;
  
  	vma->vm_private_data = vm_priv;

  	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;

  
  	vma->vm_ops = &gntalloc_vmops;
  
  	for (i = 0; i < count; i++) {
  		gref->users++;
  		rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
  				gref->page);
  		if (rv)
  			goto out_unlock;
  
  		gref = list_entry(gref->next_file.next,
  				struct gntalloc_gref, next_file);
  	}
  	rv = 0;
  
  out_unlock:

  	mutex_unlock(&gref_mutex);

  	return rv;
  }
  
  static const struct file_operations gntalloc_fops = {
  	.owner = THIS_MODULE,
  	.open = gntalloc_open,
  	.release = gntalloc_release,
  	.unlocked_ioctl = gntalloc_ioctl,
  	.mmap = gntalloc_mmap
  };
  
  /*
   * -------------------------------------
   * Module creation/destruction.
   * -------------------------------------
   */
  static struct miscdevice gntalloc_miscdev = {
  	.minor	= MISC_DYNAMIC_MINOR,
  	.name	= "xen/gntalloc",
  	.fops	= &gntalloc_fops,
  };
  
  static int __init gntalloc_init(void)
  {
  	int err;
  
  	if (!xen_domain())
  		return -ENODEV;
  
  	err = misc_register(&gntalloc_miscdev);
  	if (err != 0) {

  		pr_err("Could not register misc gntalloc device
  ");

  		return err;
  	}
  
  	pr_debug("Created grant allocation device at %d,%d
  ",
  			MISC_MAJOR, gntalloc_miscdev.minor);
  
  	return 0;
  }
  
  static void __exit gntalloc_exit(void)
  {
  	misc_deregister(&gntalloc_miscdev);
  }
  
  module_init(gntalloc_init);
  module_exit(gntalloc_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
  		"Daniel De Graaf <dgdegra@tycho.nsa.gov>");
  MODULE_DESCRIPTION("User-space grant reference allocator driver");