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612 lines
15 KiB
612 lines
15 KiB
/****************************************************************************** |
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* gntalloc.c |
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* |
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* Device for creating grant references (in user-space) that may be shared |
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* with other domains. |
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* |
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* This program is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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* GNU General Public License for more details. |
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* |
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* You should have received a copy of the GNU General Public License |
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* along with this program; if not, write to the Free Software |
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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*/ |
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|
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/* |
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* This driver exists to allow userspace programs in Linux to allocate kernel |
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* memory that will later be shared with another domain. Without this device, |
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* Linux userspace programs cannot create grant references. |
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* |
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* How this stuff works: |
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* X -> granting a page to Y |
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* Y -> mapping the grant from X |
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* |
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* 1. X uses the gntalloc device to allocate a page of kernel memory, P. |
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* 2. X creates an entry in the grant table that says domid(Y) can access P. |
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* This is done without a hypercall unless the grant table needs expansion. |
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* 3. X gives the grant reference identifier, GREF, to Y. |
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* 4. Y maps the page, either directly into kernel memory for use in a backend |
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* driver, or via a the gntdev device to map into the address space of an |
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* application running in Y. This is the first point at which Xen does any |
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* tracking of the page. |
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* 5. A program in X mmap()s a segment of the gntalloc device that corresponds |
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* to the shared page, and can now communicate with Y over the shared page. |
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* |
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* |
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* NOTE TO USERSPACE LIBRARIES: |
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* The grant allocation and mmap()ing are, naturally, two separate operations. |
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* You set up the sharing by calling the create ioctl() and then the mmap(). |
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* Teardown requires munmap() and either close() or ioctl(). |
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* |
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* WARNING: Since Xen does not allow a guest to forcibly end the use of a grant |
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* reference, this device can be used to consume kernel memory by leaving grant |
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* references mapped by another domain when an application exits. Therefore, |
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* there is a global limit on the number of pages that can be allocated. When |
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* all references to the page are unmapped, it will be freed during the next |
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* grant operation. |
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*/ |
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|
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#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt |
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#include <linux/atomic.h> |
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#include <linux/module.h> |
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#include <linux/miscdevice.h> |
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#include <linux/kernel.h> |
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#include <linux/init.h> |
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#include <linux/slab.h> |
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#include <linux/fs.h> |
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#include <linux/device.h> |
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#include <linux/mm.h> |
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#include <linux/uaccess.h> |
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#include <linux/types.h> |
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#include <linux/list.h> |
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#include <linux/highmem.h> |
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#include <xen/xen.h> |
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#include <xen/page.h> |
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#include <xen/grant_table.h> |
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#include <xen/gntalloc.h> |
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#include <xen/events.h> |
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static int limit = 1024; |
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module_param(limit, int, 0644); |
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MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by " |
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"the gntalloc device"); |
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static LIST_HEAD(gref_list); |
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static DEFINE_MUTEX(gref_mutex); |
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static int gref_size; |
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struct notify_info { |
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uint16_t pgoff:12; /* Bits 0-11: Offset of the byte to clear */ |
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uint16_t flags:2; /* Bits 12-13: Unmap notification flags */ |
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int event; /* Port (event channel) to notify */ |
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}; |
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/* Metadata on a grant reference. */ |
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struct gntalloc_gref { |
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struct list_head next_gref; /* list entry gref_list */ |
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struct list_head next_file; /* list entry file->list, if open */ |
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struct page *page; /* The shared page */ |
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uint64_t file_index; /* File offset for mmap() */ |
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unsigned int users; /* Use count - when zero, waiting on Xen */ |
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grant_ref_t gref_id; /* The grant reference number */ |
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struct notify_info notify; /* Unmap notification */ |
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}; |
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struct gntalloc_file_private_data { |
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struct list_head list; |
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uint64_t index; |
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}; |
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struct gntalloc_vma_private_data { |
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struct gntalloc_gref *gref; |
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int users; |
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int count; |
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}; |
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static void __del_gref(struct gntalloc_gref *gref); |
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|
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static void do_cleanup(void) |
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{ |
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struct gntalloc_gref *gref, *n; |
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list_for_each_entry_safe(gref, n, &gref_list, next_gref) { |
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if (!gref->users) |
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__del_gref(gref); |
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} |
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} |
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static int add_grefs(struct ioctl_gntalloc_alloc_gref *op, |
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uint32_t *gref_ids, struct gntalloc_file_private_data *priv) |
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{ |
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int i, rc, readonly; |
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LIST_HEAD(queue_gref); |
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LIST_HEAD(queue_file); |
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struct gntalloc_gref *gref, *next; |
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readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE); |
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for (i = 0; i < op->count; i++) { |
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gref = kzalloc(sizeof(*gref), GFP_KERNEL); |
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if (!gref) { |
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rc = -ENOMEM; |
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goto undo; |
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} |
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list_add_tail(&gref->next_gref, &queue_gref); |
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list_add_tail(&gref->next_file, &queue_file); |
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gref->users = 1; |
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gref->file_index = op->index + i * PAGE_SIZE; |
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gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO); |
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if (!gref->page) { |
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rc = -ENOMEM; |
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goto undo; |
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} |
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/* Grant foreign access to the page. */ |
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rc = gnttab_grant_foreign_access(op->domid, |
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xen_page_to_gfn(gref->page), |
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readonly); |
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if (rc < 0) |
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goto undo; |
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gref_ids[i] = gref->gref_id = rc; |
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} |
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/* Add to gref lists. */ |
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mutex_lock(&gref_mutex); |
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list_splice_tail(&queue_gref, &gref_list); |
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list_splice_tail(&queue_file, &priv->list); |
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mutex_unlock(&gref_mutex); |
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return 0; |
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undo: |
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mutex_lock(&gref_mutex); |
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gref_size -= (op->count - i); |
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list_for_each_entry_safe(gref, next, &queue_file, next_file) { |
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list_del(&gref->next_file); |
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__del_gref(gref); |
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} |
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/* It's possible for the target domain to map the just-allocated grant |
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* references by blindly guessing their IDs; if this is done, then |
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* __del_gref will leave them in the queue_gref list. They need to be |
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* added to the global list so that we can free them when they are no |
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* longer referenced. |
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*/ |
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if (unlikely(!list_empty(&queue_gref))) |
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list_splice_tail(&queue_gref, &gref_list); |
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mutex_unlock(&gref_mutex); |
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return rc; |
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} |
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static void __del_gref(struct gntalloc_gref *gref) |
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{ |
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if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) { |
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uint8_t *tmp = kmap(gref->page); |
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tmp[gref->notify.pgoff] = 0; |
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kunmap(gref->page); |
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} |
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if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) { |
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notify_remote_via_evtchn(gref->notify.event); |
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evtchn_put(gref->notify.event); |
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} |
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gref->notify.flags = 0; |
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if (gref->gref_id) { |
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if (gnttab_query_foreign_access(gref->gref_id)) |
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return; |
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if (!gnttab_end_foreign_access_ref(gref->gref_id, 0)) |
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return; |
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gnttab_free_grant_reference(gref->gref_id); |
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} |
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gref_size--; |
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list_del(&gref->next_gref); |
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if (gref->page) |
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__free_page(gref->page); |
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kfree(gref); |
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} |
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/* finds contiguous grant references in a file, returns the first */ |
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static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv, |
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uint64_t index, uint32_t count) |
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{ |
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struct gntalloc_gref *rv = NULL, *gref; |
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list_for_each_entry(gref, &priv->list, next_file) { |
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if (gref->file_index == index && !rv) |
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rv = gref; |
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if (rv) { |
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if (gref->file_index != index) |
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return NULL; |
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index += PAGE_SIZE; |
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count--; |
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if (count == 0) |
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return rv; |
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} |
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} |
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return NULL; |
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} |
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/* |
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* ------------------------------------- |
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* File operations. |
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* ------------------------------------- |
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*/ |
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static int gntalloc_open(struct inode *inode, struct file *filp) |
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{ |
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struct gntalloc_file_private_data *priv; |
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priv = kzalloc(sizeof(*priv), GFP_KERNEL); |
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if (!priv) |
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goto out_nomem; |
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INIT_LIST_HEAD(&priv->list); |
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filp->private_data = priv; |
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pr_debug("%s: priv %p\n", __func__, priv); |
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return 0; |
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out_nomem: |
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return -ENOMEM; |
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} |
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static int gntalloc_release(struct inode *inode, struct file *filp) |
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{ |
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struct gntalloc_file_private_data *priv = filp->private_data; |
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struct gntalloc_gref *gref; |
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pr_debug("%s: priv %p\n", __func__, priv); |
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mutex_lock(&gref_mutex); |
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while (!list_empty(&priv->list)) { |
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gref = list_entry(priv->list.next, |
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struct gntalloc_gref, next_file); |
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list_del(&gref->next_file); |
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gref->users--; |
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if (gref->users == 0) |
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__del_gref(gref); |
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} |
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kfree(priv); |
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mutex_unlock(&gref_mutex); |
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return 0; |
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} |
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static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv, |
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struct ioctl_gntalloc_alloc_gref __user *arg) |
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{ |
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int rc = 0; |
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struct ioctl_gntalloc_alloc_gref op; |
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uint32_t *gref_ids; |
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pr_debug("%s: priv %p\n", __func__, priv); |
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if (copy_from_user(&op, arg, sizeof(op))) { |
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rc = -EFAULT; |
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goto out; |
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} |
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gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_KERNEL); |
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if (!gref_ids) { |
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rc = -ENOMEM; |
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goto out; |
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} |
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mutex_lock(&gref_mutex); |
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/* Clean up pages that were at zero (local) users but were still mapped |
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* by remote domains. Since those pages count towards the limit that we |
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* are about to enforce, removing them here is a good idea. |
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*/ |
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do_cleanup(); |
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if (gref_size + op.count > limit) { |
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mutex_unlock(&gref_mutex); |
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rc = -ENOSPC; |
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goto out_free; |
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} |
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gref_size += op.count; |
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op.index = priv->index; |
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priv->index += op.count * PAGE_SIZE; |
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mutex_unlock(&gref_mutex); |
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rc = add_grefs(&op, gref_ids, priv); |
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if (rc < 0) |
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goto out_free; |
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/* Once we finish add_grefs, it is unsafe to touch the new reference, |
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* since it is possible for a concurrent ioctl to remove it (by guessing |
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* its index). If the userspace application doesn't provide valid memory |
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* to write the IDs to, then it will need to close the file in order to |
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* release - which it will do by segfaulting when it tries to access the |
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* IDs to close them. |
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*/ |
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if (copy_to_user(arg, &op, sizeof(op))) { |
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rc = -EFAULT; |
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goto out_free; |
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} |
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if (copy_to_user(arg->gref_ids, gref_ids, |
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sizeof(gref_ids[0]) * op.count)) { |
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rc = -EFAULT; |
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goto out_free; |
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} |
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out_free: |
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kfree(gref_ids); |
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out: |
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return rc; |
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} |
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static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv, |
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void __user *arg) |
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{ |
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int i, rc = 0; |
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struct ioctl_gntalloc_dealloc_gref op; |
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struct gntalloc_gref *gref, *n; |
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pr_debug("%s: priv %p\n", __func__, priv); |
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if (copy_from_user(&op, arg, sizeof(op))) { |
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rc = -EFAULT; |
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goto dealloc_grant_out; |
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} |
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mutex_lock(&gref_mutex); |
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gref = find_grefs(priv, op.index, op.count); |
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if (gref) { |
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/* Remove from the file list only, and decrease reference count. |
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* The later call to do_cleanup() will remove from gref_list and |
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* free the memory if the pages aren't mapped anywhere. |
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*/ |
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for (i = 0; i < op.count; i++) { |
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n = list_entry(gref->next_file.next, |
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struct gntalloc_gref, next_file); |
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list_del(&gref->next_file); |
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gref->users--; |
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gref = n; |
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} |
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} else { |
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rc = -EINVAL; |
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} |
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do_cleanup(); |
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mutex_unlock(&gref_mutex); |
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dealloc_grant_out: |
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return rc; |
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} |
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static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv, |
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void __user *arg) |
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{ |
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struct ioctl_gntalloc_unmap_notify op; |
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struct gntalloc_gref *gref; |
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uint64_t index; |
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int pgoff; |
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int rc; |
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if (copy_from_user(&op, arg, sizeof(op))) |
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return -EFAULT; |
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index = op.index & ~(PAGE_SIZE - 1); |
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pgoff = op.index & (PAGE_SIZE - 1); |
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mutex_lock(&gref_mutex); |
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gref = find_grefs(priv, index, 1); |
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if (!gref) { |
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rc = -ENOENT; |
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goto unlock_out; |
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} |
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if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) { |
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rc = -EINVAL; |
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goto unlock_out; |
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} |
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|
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/* We need to grab a reference to the event channel we are going to use |
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* to send the notify before releasing the reference we may already have |
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* (if someone has called this ioctl twice). This is required so that |
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* it is possible to change the clear_byte part of the notification |
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* without disturbing the event channel part, which may now be the last |
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* reference to that event channel. |
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*/ |
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if (op.action & UNMAP_NOTIFY_SEND_EVENT) { |
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if (evtchn_get(op.event_channel_port)) { |
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rc = -EINVAL; |
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goto unlock_out; |
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} |
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} |
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if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) |
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evtchn_put(gref->notify.event); |
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gref->notify.flags = op.action; |
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gref->notify.pgoff = pgoff; |
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gref->notify.event = op.event_channel_port; |
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rc = 0; |
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unlock_out: |
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mutex_unlock(&gref_mutex); |
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return rc; |
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} |
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static long gntalloc_ioctl(struct file *filp, unsigned int cmd, |
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unsigned long arg) |
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{ |
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struct gntalloc_file_private_data *priv = filp->private_data; |
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switch (cmd) { |
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case IOCTL_GNTALLOC_ALLOC_GREF: |
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return gntalloc_ioctl_alloc(priv, (void __user *)arg); |
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|
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case IOCTL_GNTALLOC_DEALLOC_GREF: |
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return gntalloc_ioctl_dealloc(priv, (void __user *)arg); |
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case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY: |
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return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg); |
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default: |
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return -ENOIOCTLCMD; |
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} |
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return 0; |
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} |
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static void gntalloc_vma_open(struct vm_area_struct *vma) |
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{ |
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struct gntalloc_vma_private_data *priv = vma->vm_private_data; |
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if (!priv) |
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return; |
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mutex_lock(&gref_mutex); |
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priv->users++; |
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mutex_unlock(&gref_mutex); |
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} |
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static void gntalloc_vma_close(struct vm_area_struct *vma) |
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{ |
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struct gntalloc_vma_private_data *priv = vma->vm_private_data; |
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struct gntalloc_gref *gref, *next; |
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int i; |
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if (!priv) |
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return; |
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mutex_lock(&gref_mutex); |
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priv->users--; |
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if (priv->users == 0) { |
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gref = priv->gref; |
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for (i = 0; i < priv->count; i++) { |
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gref->users--; |
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next = list_entry(gref->next_gref.next, |
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struct gntalloc_gref, next_gref); |
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if (gref->users == 0) |
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__del_gref(gref); |
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gref = next; |
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} |
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kfree(priv); |
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} |
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mutex_unlock(&gref_mutex); |
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} |
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static const struct vm_operations_struct gntalloc_vmops = { |
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.open = gntalloc_vma_open, |
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.close = gntalloc_vma_close, |
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}; |
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|
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static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma) |
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{ |
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struct gntalloc_file_private_data *priv = filp->private_data; |
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struct gntalloc_vma_private_data *vm_priv; |
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struct gntalloc_gref *gref; |
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int count = vma_pages(vma); |
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int rv, i; |
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if (!(vma->vm_flags & VM_SHARED)) { |
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pr_err("%s: Mapping must be shared\n", __func__); |
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return -EINVAL; |
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} |
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vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL); |
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if (!vm_priv) |
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return -ENOMEM; |
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mutex_lock(&gref_mutex); |
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|
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pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__, |
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priv, vm_priv, vma->vm_pgoff, count); |
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|
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gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count); |
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if (gref == NULL) { |
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rv = -ENOENT; |
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pr_debug("%s: Could not find grant reference", |
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__func__); |
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kfree(vm_priv); |
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goto out_unlock; |
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} |
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vm_priv->gref = gref; |
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vm_priv->users = 1; |
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vm_priv->count = count; |
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vma->vm_private_data = vm_priv; |
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vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP; |
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vma->vm_ops = &gntalloc_vmops; |
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for (i = 0; i < count; i++) { |
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gref->users++; |
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rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE, |
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gref->page); |
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if (rv) |
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goto out_unlock; |
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gref = list_entry(gref->next_file.next, |
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struct gntalloc_gref, next_file); |
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} |
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rv = 0; |
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out_unlock: |
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mutex_unlock(&gref_mutex); |
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return rv; |
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} |
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static const struct file_operations gntalloc_fops = { |
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.owner = THIS_MODULE, |
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.open = gntalloc_open, |
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.release = gntalloc_release, |
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.unlocked_ioctl = gntalloc_ioctl, |
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.mmap = gntalloc_mmap |
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}; |
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|
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/* |
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* ------------------------------------- |
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* Module creation/destruction. |
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* ------------------------------------- |
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*/ |
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static struct miscdevice gntalloc_miscdev = { |
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.minor = MISC_DYNAMIC_MINOR, |
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.name = "xen/gntalloc", |
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.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\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 <[email protected]>, " |
|
"Daniel De Graaf <[email protected]>"); |
|
MODULE_DESCRIPTION("User-space grant reference allocator driver");
|
|
|