xen-gntalloc: Userspace grant allocation driver
This allows a userspace application to allocate a shared page for implementing inter-domain communication or device drivers. These shared pages can be mapped using the gntdev device or by the kernel in another domain. Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Daniel De Graaf
Konrad Rzeszutek Wilk
parent
aab8f11a6b
commit
dd3140588d
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@ -80,6 +80,14 @@ config XEN_GNTDEV
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help
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Allows userspace processes to use grants.
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config XEN_GRANT_DEV_ALLOC
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tristate "User-space grant reference allocator driver"
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depends on XEN
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help
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Allows userspace processes to create pages with access granted
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to other domains. This can be used to implement frontend drivers
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or as part of an inter-domain shared memory channel.
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config XEN_PLATFORM_PCI
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tristate "xen platform pci device driver"
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depends on XEN_PVHVM && PCI
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@ -10,6 +10,7 @@ obj-$(CONFIG_XEN_XENCOMM) += xencomm.o
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obj-$(CONFIG_XEN_BALLOON) += balloon.o
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obj-$(CONFIG_XEN_DEV_EVTCHN) += xen-evtchn.o
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obj-$(CONFIG_XEN_GNTDEV) += xen-gntdev.o
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obj-$(CONFIG_XEN_GRANT_DEV_ALLOC) += xen-gntalloc.o
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obj-$(CONFIG_XENFS) += xenfs/
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obj-$(CONFIG_XEN_SYS_HYPERVISOR) += sys-hypervisor.o
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obj-$(CONFIG_XEN_PLATFORM_PCI) += xen-platform-pci.o
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@ -18,5 +19,6 @@ obj-$(CONFIG_XEN_DOM0) += pci.o
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xen-evtchn-y := evtchn.o
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xen-gntdev-y := gntdev.o
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xen-gntalloc-y := gntalloc.o
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xen-platform-pci-y := platform-pci.o
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@ -0,0 +1,486 @@
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/******************************************************************************
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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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* 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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#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 <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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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_SPINLOCK(gref_lock);
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static int gref_size;
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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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};
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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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static void __del_gref(struct gntalloc_gref *gref);
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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;
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readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
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rc = -ENOMEM;
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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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goto undo;
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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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goto undo;
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/* Grant foreign access to the page. */
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gref->gref_id = gnttab_grant_foreign_access(op->domid,
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pfn_to_mfn(page_to_pfn(gref->page)), readonly);
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if (gref->gref_id < 0) {
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rc = gref->gref_id;
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goto undo;
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}
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gref_ids[i] = gref->gref_id;
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}
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/* Add to gref lists. */
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spin_lock(&gref_lock);
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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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spin_unlock(&gref_lock);
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return 0;
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undo:
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spin_lock(&gref_lock);
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gref_size -= (op->count - i);
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list_for_each_entry(gref, &queue_file, next_file) {
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/* __del_gref does not remove from queue_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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spin_unlock(&gref_lock);
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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->gref_id > 0) {
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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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}
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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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spin_lock(&gref_lock);
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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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spin_unlock(&gref_lock);
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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 = kzalloc(sizeof(gref_ids[0]) * op.count, GFP_TEMPORARY);
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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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spin_lock(&gref_lock);
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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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spin_unlock(&gref_lock);
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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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spin_unlock(&gref_lock);
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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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spin_lock(&gref_lock);
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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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spin_unlock(&gref_lock);
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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(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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case IOCTL_GNTALLOC_DEALLOC_GREF:
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return gntalloc_ioctl_dealloc(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_close(struct vm_area_struct *vma)
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{
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struct gntalloc_gref *gref = vma->vm_private_data;
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if (!gref)
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return;
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spin_lock(&gref_lock);
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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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spin_unlock(&gref_lock);
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}
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static struct vm_operations_struct gntalloc_vmops = {
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.close = gntalloc_vma_close,
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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_gref *gref;
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int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
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int rv, i;
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pr_debug("%s: priv %p, page %lu+%d\n", __func__,
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priv, vma->vm_pgoff, count);
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if (!(vma->vm_flags & VM_SHARED)) {
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printk(KERN_ERR "%s: Mapping must be shared.\n", __func__);
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return -EINVAL;
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}
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spin_lock(&gref_lock);
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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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goto out_unlock;
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}
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vma->vm_private_data = gref;
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vma->vm_flags |= VM_RESERVED;
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vma->vm_flags |= VM_DONTCOPY;
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vma->vm_flags |= VM_PFNMAP | VM_PFN_AT_MMAP;
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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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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");
|
||||
|
|
@ -0,0 +1,50 @@
|
|||
/******************************************************************************
|
||||
* gntalloc.h
|
||||
*
|
||||
* Interface to /dev/xen/gntalloc.
|
||||
*
|
||||
* Author: Daniel De Graaf <dgdegra@tycho.nsa.gov>
|
||||
*
|
||||
* This file is in the public domain.
|
||||
*/
|
||||
|
||||
#ifndef __LINUX_PUBLIC_GNTALLOC_H__
|
||||
#define __LINUX_PUBLIC_GNTALLOC_H__
|
||||
|
||||
/*
|
||||
* Allocates a new page and creates a new grant reference.
|
||||
*/
|
||||
#define IOCTL_GNTALLOC_ALLOC_GREF \
|
||||
_IOC(_IOC_NONE, 'G', 5, sizeof(struct ioctl_gntalloc_alloc_gref))
|
||||
struct ioctl_gntalloc_alloc_gref {
|
||||
/* IN parameters */
|
||||
/* The ID of the domain to be given access to the grants. */
|
||||
uint16_t domid;
|
||||
/* Flags for this mapping */
|
||||
uint16_t flags;
|
||||
/* Number of pages to map */
|
||||
uint32_t count;
|
||||
/* OUT parameters */
|
||||
/* The offset to be used on a subsequent call to mmap(). */
|
||||
uint64_t index;
|
||||
/* The grant references of the newly created grant, one per page */
|
||||
/* Variable size, depending on count */
|
||||
uint32_t gref_ids[1];
|
||||
};
|
||||
|
||||
#define GNTALLOC_FLAG_WRITABLE 1
|
||||
|
||||
/*
|
||||
* Deallocates the grant reference, allowing the associated page to be freed if
|
||||
* no other domains are using it.
|
||||
*/
|
||||
#define IOCTL_GNTALLOC_DEALLOC_GREF \
|
||||
_IOC(_IOC_NONE, 'G', 6, sizeof(struct ioctl_gntalloc_dealloc_gref))
|
||||
struct ioctl_gntalloc_dealloc_gref {
|
||||
/* IN parameters */
|
||||
/* The offset returned in the map operation */
|
||||
uint64_t index;
|
||||
/* Number of references to unmap */
|
||||
uint32_t count;
|
||||
};
|
||||
#endif /* __LINUX_PUBLIC_GNTALLOC_H__ */
|
||||
Loading…
Reference in New Issue