/******************************************************************************
* 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.
*/
#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_SPINLOCK(gref_lock);
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;
};
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;
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. */
gref->gref_id = gnttab_grant_foreign_access(op->domid,
pfn_to_mfn(page_to_pfn(gref->page)), readonly);
if (gref->gref_id < 0) {
rc = gref->gref_id;
goto undo;
}
gref_ids[i] = gref->gref_id;
}
/* Add to gref lists. */
spin_lock(&gref_lock);
list_splice_tail(&queue_gref, &gref_list);
list_splice_tail(&queue_file, &priv->list);
spin_unlock(&gref_lock);
return 0;
undo:
spin_lock(&gref_lock);
gref_size -= (op->count - i);
list_for_each_entry(gref, &queue_file, next_file) {
/* __del_gref does not remove from queue_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);
spin_unlock(&gref_lock);
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);
gref->notify.flags = 0;
if (gref->gref_id > 0) {
if (gnttab_query_foreign_access(gref->gref_id))
return;
if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
return;
}
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\n", __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\n", __func__, priv);
spin_lock(&gref_lock);
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);
spin_unlock(&gref_lock);
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\n", __func__, priv);
if (copy_from_user(&op, arg, sizeof(op))) {
rc = -EFAULT;
goto out;
}
gref_ids = kzalloc(sizeof(gref_ids[0]) * op.count, GFP_TEMPORARY);
if (!gref_ids) {
rc = -ENOMEM;
goto out;
}
spin_lock(&gref_lock);
/* 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) {
spin_unlock(&gref_lock);
rc = -ENOSPC;
goto out_free;
}
gref_size += op.count;
op.index = priv->index;
priv->index += op.count * PAGE_SIZE;
spin_unlock(&gref_lock);
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\n", __func__, priv);
if (copy_from_user(&op, arg, sizeof(op))) {
rc = -EFAULT;
goto dealloc_grant_out;
}
spin_lock(&gref_lock);
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();
spin_unlock(&gref_lock);
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);
spin_lock(&gref_lock);
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;
}
gref->notify.flags = op.action;
gref->notify.pgoff = pgoff;
gref->notify.event = op.event_channel_port;
rc = 0;
unlock_out:
spin_unlock(&gref_lock);
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_gref *gref = vma->vm_private_data;
if (!gref)
return;
spin_lock(&gref_lock);
gref->users++;
spin_unlock(&gref_lock);
}
static void gntalloc_vma_close(struct vm_area_struct *vma)
{
struct gntalloc_gref *gref = vma->vm_private_data;
if (!gref)
return;
spin_lock(&gref_lock);
gref->users--;
if (gref->users == 0)
__del_gref(gref);
spin_unlock(&gref_lock);
}
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_gref *gref;
int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
int rv, i;
pr_debug("%s: priv %p, page %lu+%d\n", __func__,
priv, vma->vm_pgoff, count);
if (!(vma->vm_flags & VM_SHARED)) {
printk(KERN_ERR "%s: Mapping must be shared.\n", __func__);
return -EINVAL;
}
spin_lock(&gref_lock);
gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
if (gref == NULL) {
rv = -ENOENT;
pr_debug("%s: Could not find grant reference",
__func__);
goto out_unlock;
}
vma->vm_private_data = gref;
vma->vm_flags |= VM_RESERVED;
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:
spin_unlock(&gref_lock);
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) {
printk(KERN_ERR "Could not register misc gntalloc device\n");
return err;
}
pr_debug("Created grant allocation device at %d,%d\n",
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");
