| /****************************************************************************** |
| * 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 = kcalloc(op.count, sizeof(gref_ids[0]), 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"); |