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|
/******************************************************************************
* 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.
*/
#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
#include <linux/atomic.h>
#include <linux/module.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/highmem.h>
#include <xen/xen.h>
#include <xen/page.h>
#include <xen/grant_table.h>
#include <xen/gntalloc.h>
#include <xen/events.h>
static int limit = 1024;
module_param(limit, int, 0644);
MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
"the gntalloc device");
static LIST_HEAD(gref_list);
static DEFINE_MUTEX(gref_mutex);
static int gref_size;
struct notify_info {
uint16_t pgoff:12; /* Bits 0-11: Offset of the byte to clear */
uint16_t flags:2; /* Bits 12-13: Unmap notification flags */
int event; /* Port (event channel) to notify */
};
/* Metadata on a grant reference. */
struct gntalloc_gref {
struct list_head next_gref; /* list entry gref_list */
struct list_head next_file; /* list entry file->list, if open */
struct page *page; /* The shared page */
uint64_t file_index; /* File offset for mmap() */
unsigned int users; /* Use count - when zero, waiting on Xen */
grant_ref_t gref_id; /* The grant reference number */
struct notify_info notify; /* Unmap notification */
};
struct gntalloc_file_private_data {
struct list_head list;
uint64_t index;
};
struct gntalloc_vma_private_data {
struct gntalloc_gref *gref;
int users;
int count;
};
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, *next;
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. */
rc = gnttab_grant_foreign_access(op->domid,
pfn_to_mfn(page_to_pfn(gref->page)), readonly);
if (rc < 0)
goto undo;
gref_ids[i] = gref->gref_id = rc;
}
/* Add to gref lists. */
mutex_lock(&gref_mutex);
list_splice_tail(&queue_gref, &gref_list);
list_splice_tail(&queue_file, &priv->list);
mutex_unlock(&gref_mutex);
return 0;
undo:
mutex_lock(&gref_mutex);
gref_size -= (op->count - i);
list_for_each_entry_safe(gref, next, &queue_file, next_file) {
list_del(&gref->next_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);
mutex_unlock(&gref_mutex);
return rc;
}
static void __del_gref(struct gntalloc_gref *gref)
{
if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
uint8_t *tmp = kmap(gref->page);
tmp[gref->notify.pgoff] = 0;
kunmap(gref->page);
}
if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
notify_remote_via_evtchn(gref->notify.event);
evtchn_put(gref->notify.event);
}
gref->notify.flags = 0;
if (gref->gref_id) {
if (gnttab_query_foreign_access(gref->gref_id))
return;
if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
return;
gnttab_free_grant_reference(gref->gref_id);
}
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
|