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@xxxxxxxxxxxxx>
---
drivers/xen/Kconfig | 7 +
drivers/xen/Makefile | 2 +
drivers/xen/gntalloc.c | 456 ++++++++++++++++++++++++++++++++++++++++++++++++
include/xen/gntalloc.h | 68 +++++++
4 files changed, 533 insertions(+), 0 deletions(-)
create mode 100644 drivers/xen/gntalloc.c
create mode 100644 include/xen/gntalloc.h
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index fa9982e..8398cb0 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -180,6 +180,13 @@ config XEN_GNTDEV
help
Allows userspace processes use grants.
+config XEN_GRANT_DEV_ALLOC
+ tristate "User-space grant reference allocator driver"
+ depends on XEN
+ help
+ Allows userspace processes to create pages with access granted
+ to other domains.
+
config XEN_S3
def_bool y
depends on XEN_DOM0 && ACPI
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index ef1ea63..9814c1d 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -10,6 +10,7 @@ obj-$(CONFIG_XEN_XENCOMM) += xencomm.o
obj-$(CONFIG_XEN_BALLOON) += balloon.o
obj-$(CONFIG_XEN_DEV_EVTCHN) += xen-evtchn.o
obj-$(CONFIG_XEN_GNTDEV) += xen-gntdev.o
+obj-$(CONFIG_XEN_GRANT_DEV_ALLOC) += xen-gntalloc.o
obj-$(CONFIG_XEN_PCIDEV_BACKEND) += pciback/
obj-$(CONFIG_XEN_BLKDEV_BACKEND) += blkback/
obj-$(CONFIG_XEN_BLKDEV_TAP) += blktap/
@@ -25,3 +26,4 @@ obj-$(CONFIG_XEN_PLATFORM_PCI) += platform-pci.o
xen-evtchn-y := evtchn.o
xen-gntdev-y := gntdev.o
+xen-gntalloc-y := gntalloc.o
diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
new file mode 100644
index 0000000..f26adfd
--- /dev/null
+++ b/drivers/xen/gntalloc.c
@@ -0,0 +1,456 @@
+/******************************************************************************
+ * 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.
+ * 3. X gives the grant reference identifier, GREF, to Y.
+ * 4. A program in Y uses the gntdev device to map the page (owned by X
+ * and identified by GREF) into domain(Y) and then into the address
+ * space of the program. Behind the scenes, this requires a
+ * hypercall in which Xen modifies the host CPU page tables to
+ * perform the sharing -- that's where the actual cross-domain mapping
+ * occurs.
+ * 5. A program in X mmap()s a segment of the gntalloc device that
+ * corresponds to the shared page.
+ * 6. The two userspace programs can now communicate 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(). You must tear down the sharing in the reverse order
+ * (munmap() and then the destroy 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 <asm/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 <asm/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 debug = 0;
+module_param(debug, int, 0644);
+
+static int limit = 1024;
+module_param(limit, int, 0644);
+
+static LIST_HEAD(gref_list);
+static DEFINE_SPINLOCK(gref_lock);
+static int gref_size = 0;
+
+/* Metadata on a grant reference. */
+struct gntalloc_gref {
+ struct list_head next_all; /* list entry gref_list */
+ struct list_head next_file; /* list entry file->list, if open */
+ domid_t foreign_domid; /* The ID of the domain to share with. */
+ grant_ref_t gref_id; /* The grant reference number. */
+ unsigned int users; /* Use count - when zero, waiting on Xen */
+ struct page* page; /* The shared page. */
+};
+
+struct gntalloc_file_private_data {
+ struct list_head list;
+};
+
+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_all) {
+ if (!gref->users)
+ __del_gref(gref);
+ }
+}
+
+
+static int add_gref(domid_t foreign_domid, uint32_t readonly,
+ struct gntalloc_file_private_data *priv)
+{
+ int rc;
+ struct gntalloc_gref *gref;
+
+ rc = -ENOMEM;
+ spin_lock(&gref_lock);
+ do_cleanup();
+ if (gref_size >= limit) {
+ spin_unlock(&gref_lock);
+ rc = -ENOSPC;
+ goto out;
+ }
+ gref_size++;
+ spin_unlock(&gref_lock);
+
+ gref = kzalloc(sizeof(*gref), GFP_KERNEL);
+ if (!gref)
+ goto out;
+
+ gref->foreign_domid = foreign_domid;
+ gref->users = 1;
+
+ /* Allocate the page to share. */
+ gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
+ if (!gref->page)
+ goto out_nopage;
+
+ /* Grant foreign access to the page. */
+ gref->gref_id = gnttab_grant_foreign_access(foreign_domid,
+ pfn_to_mfn(page_to_pfn(gref->page)), readonly);
+ if (gref->gref_id < 0) {
+ printk(KERN_ERR "%s: failed to grant foreign access for mfn "
+ "%lu to domain %u\n", __func__,
+ pfn_to_mfn(page_to_pfn(gref->page)), foreign_domid);
+ rc = -EFAULT;
+ goto out_no_foreign_gref;
+ }
+
+ /* Add to gref lists. */
+ spin_lock(&gref_lock);
+ list_add_tail(&gref->next_all, &gref_list);
+ list_add_tail(&gref->next_file, &priv->list);
+ spin_unlock(&gref_lock);
+
+ return gref->gref_id;
+
+out_no_foreign_gref:
+ __free_page(gref->page);
+out_nopage:
+ kfree(gref);
+out:
+ return rc;
+}
+
+static void __del_gref(struct gntalloc_gref *gref)
+{
+ 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_all);
+
+ __free_page(gref->page);
+ kfree(gref);
+}
+
+static struct gntalloc_gref* find_gref(struct gntalloc_file_private_data *priv,
+ grant_ref_t gref_id)
+{
+ struct gntalloc_gref *gref;
+ list_for_each_entry(gref, &priv->list, next_file) {
+ if (gref->gref_id == gref_id)
+ return gref;
+ }
+ return NULL;
+}
+
+/*
+ * -------------------------------------
+ * File operations.
+ * -------------------------------------
+ */
+static int gntalloc_open(struct inode *inode, struct file *filp)
+{
+ struct gntalloc_file_private_data *priv;
+
+ try_module_get(THIS_MODULE);
+
+ priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+ if (!priv)
+ goto out_nomem;
+ INIT_LIST_HEAD(&priv->list);
+
+ filp->private_data = priv;
+
+ if (debug)
+ printk("%s: priv %p\n", __FUNCTION__, 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;
+
+ if (debug)
+ printk("%s: priv %p\n", __FUNCTION__, 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);
+
+ module_put(THIS_MODULE);
+
+ return 0;
+}
+
+static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
+ void __user *arg)
+{
+ int rc = 0;
+ struct ioctl_gntalloc_alloc_gref op;
+
+ if (debug)
+ printk("%s: priv %p\n", __FUNCTION__, priv);
+
+ if (copy_from_user(&op, arg, sizeof(op))) {
+ rc = -EFAULT;
+ goto alloc_grant_out;
+ }
+ rc = add_gref(op.foreign_domid, op.readonly, priv);
+ if (rc < 0)
+ goto alloc_grant_out;
+
+ op.gref_id = rc;
+ op.page_idx = rc;
+
+ rc = 0;
+
+ if (copy_to_user((void __user *)arg, &op, sizeof(op))) {
+ rc = -EFAULT;
+ goto alloc_grant_out;
+ }
+
+alloc_grant_out:
+ return rc;
+}
+
+static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
+ void __user *arg)
+{
+ int rc = 0;
+ struct ioctl_gntalloc_dealloc_gref op;
+ struct gntalloc_gref *gref;
+
+ if (debug)
+ printk("%s: priv %p\n", __FUNCTION__, priv);
+
+ if (copy_from_user(&op, arg, sizeof(op))) {
+ rc = -EFAULT;
+ goto dealloc_grant_out;
+ }
+
+ spin_lock(&gref_lock);
+ gref = find_gref(priv, op.gref_id);
+ if (gref) {
+ list_del(&gref->next_file);
+ gref->users--;
+ rc = 0;
+ } 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 int gntalloc_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+ struct gntalloc_gref *gref = vma->vm_private_data;
+ if (!gref)
+ return VM_FAULT_SIGBUS;
+
+ vmf->page = gref->page;
+ get_page(vmf->page);
+
+ 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 = {
+ .fault = gntalloc_vma_fault,
+ .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;
+
+ if (debug)
+ printk("%s: priv %p, page %lu\n", __func__,
+ priv, vma->vm_pgoff);
+
+ /*
+ * There is a 1-to-1 correspondence of grant references to shared
+ * pages, so it only makes sense to map exactly one page per
+ * call to mmap().
+ */
+ if (((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) != 1) {
+ printk(KERN_ERR "%s: Only one page can be memory-mapped "
+ "per grant reference.\n", __func__);
+ return -EINVAL;
+ }
+
+ if (!(vma->vm_flags & VM_SHARED)) {
+ printk(KERN_ERR "%s: Mapping must be shared.\n",
+ __func__);
+ return -EINVAL;
+ }
+
+ spin_lock(&gref_lock);
+ gref = find_gref(priv, vma->vm_pgoff);
+ if (gref == NULL) {
+ spin_unlock(&gref_lock);
+ printk(KERN_ERR "%s: Could not find a grant reference with "
+ "page index %lu.\n", __func__, vma->vm_pgoff);
+ return -ENOENT;
+ }
+ gref->users++;
+ spin_unlock(&gref_lock);
+
+ vma->vm_private_data = gref;
+
+ /* This flag prevents Bad PTE errors when the memory is unmapped. */
+ vma->vm_flags |= VM_RESERVED;
+ vma->vm_flags |= VM_DONTCOPY;
+ vma->vm_flags |= VM_IO;
+
+ vma->vm_ops = &gntalloc_vmops;
+
+ return 0;
+}
+
+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()) {
+ if (debug)
+ printk(KERN_ERR "gntalloc: You must be running Xen\n");
+ return -ENODEV;
+ }
+
+ err = misc_register(&gntalloc_miscdev);
+ if (err != 0) {
+ printk(KERN_ERR "Could not register misc gntalloc device\n");
+ return err;
+ }
+
+ if (debug)
+ printk(KERN_INFO "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@xxxxxxxxxx>, "
+ "Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("User-space grant reference allocator driver");
diff --git a/include/xen/gntalloc.h b/include/xen/gntalloc.h
new file mode 100644
index 0000000..76b70d7
--- /dev/null
+++ b/include/xen/gntalloc.h
@@ -0,0 +1,68 @@
+/******************************************************************************
+ * gntalloc.h
+ *
+ * Interface to /dev/xen/gntalloc.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#ifndef __LINUX_PUBLIC_GNTALLOC_H__
+#define __LINUX_PUBLIC_GNTALLOC_H__
+
+/*
+ * Allocates a new page and creates a new grant reference.
+ *
+ * N.B. The page_idx is really the address >> PAGE_SHIFT, meaning it's the
+ * page number and not an actual address. It must be shifted again prior
+ * to feeding it to mmap() (i.e. page_idx << PAGE_SHIFT).
+ */
+#define IOCTL_GNTALLOC_ALLOC_GREF \
+_IOC(_IOC_NONE, 'G', 1, sizeof(struct ioctl_gntalloc_alloc_gref))
+struct ioctl_gntalloc_alloc_gref {
+ /* IN parameters */
+ /* The ID of the domain creating the grant reference. */
+ domid_t owner_domid;
+ /* The ID of the domain to be given access to the grant. */
+ domid_t foreign_domid;
+ /* The type of access given to domid. */
+ uint32_t readonly;
+ /* OUT parameters */
+ /* The grant reference of the newly created grant. */
+ grant_ref_t gref_id;
+ /* The page index (page number, NOT address) for grant mmap(). */
+ uint32_t page_idx;
+};
+
+/*
+ * Deallocates the grant reference, freeing the associated page.
+ */
+#define IOCTL_GNTALLOC_DEALLOC_GREF \
+_IOC(_IOC_NONE, 'G', 2, sizeof(struct ioctl_gntalloc_dealloc_gref))
+struct ioctl_gntalloc_dealloc_gref {
+ /* IN parameter */
+ /* The grant reference to deallocate. */
+ grant_ref_t gref_id;
+};
+#endif /* __LINUX_PUBLIC_GNTALLOC_H__ */
--
1.7.2.3
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