diff options
Diffstat (limited to 'drivers/xen/gntalloc.c')
| -rw-r--r-- | drivers/xen/gntalloc.c | 486 |
1 files changed, 486 insertions, 0 deletions
diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c new file mode 100644 index 00000000000..d06bf2b4cd0 --- /dev/null +++ b/drivers/xen/gntalloc.c @@ -0,0 +1,486 @@ +/****************************************************************************** + * 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 <xen/xen.h> +#include <xen/page.h> +#include <xen/grant_table.h> +#include <xen/gntalloc.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; + +/* 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 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->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(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); + + default: + return -ENOIOCTLCMD; + } + + return 0; +} + +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 = { + .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_flags |= VM_DONTCOPY; + vma->vm_flags |= VM_PFNMAP | VM_PFN_AT_MMAP; + + 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"); |