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[Xen-devel] [PATCH 5/6] xen-gntalloc: Userspace grant allocation driver

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] [PATCH 5/6] xen-gntalloc: Userspace grant allocation driver
From: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
Date: Thu, 3 Feb 2011 12:19:03 -0500
Cc: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>, jeremy@xxxxxxxx, Ian.Campbell@xxxxxxxxxx, konrad.wilk@xxxxxxxxxx
Delivery-date: Thu, 03 Feb 2011 09:22:50 -0800
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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    |    8 +
 drivers/xen/Makefile   |    2 +
 drivers/xen/gntalloc.c |  486 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/xen/gntalloc.h |   50 +++++
 4 files changed, 546 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 19f1f3c..69d2cd5 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -142,6 +142,14 @@ config XEN_GNTDEV
        help
          Allows userspace processes to 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. This can be used to implement frontend drivers
+         or as part of an inter-domain shared memory channel.
+
 config XEN_PLATFORM_PCI
        tristate "xen platform pci device driver"
        depends on XEN_PVHVM && PCI
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 5c3b031..09364b9 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-$(CONFIG_XENFS)            += xenfs/
 obj-$(CONFIG_XEN_SYS_HYPERVISOR)       += sys-hypervisor.o
@@ -19,5 +20,6 @@ obj-$(CONFIG_XEN_DOM0)                += pci.o
 
 xen-evtchn-y                   := evtchn.o
 xen-gntdev-y                           := gntdev.o
+xen-gntalloc-y                         := gntalloc.o
 
 xen-platform-pci-y             := platform-pci.o
diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
new file mode 100644
index 0000000..d06bf2b
--- /dev/null
+++ b/drivers/xen/gntalloc.c
@@ -0,0 +1,486 @@
+/******************************************************************************
+ * gntalloc.c
+ *
+ * Device for creating grant references (in user-space) that may be shared
+ * with other domains.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+/*
+ * This driver exists to allow userspace programs in Linux to allocate kernel
+ * memory that will later be shared with another domain.  Without this device,
+ * Linux userspace programs cannot create grant references.
+ *
+ * How this stuff works:
+ *   X -> granting a page to Y
+ *   Y -> mapping the grant from X
+ *
+ *   1. X uses the gntalloc device to allocate a page of kernel memory, P.
+ *   2. X creates an entry in the grant table that says domid(Y) can access P.
+ *      This is done without a hypercall unless the grant table needs 
expansion.
+ *   3. X gives the grant reference identifier, GREF, to Y.
+ *   4. Y maps the page, either directly into kernel memory for use in a 
backend
+ *      driver, or via a the gntdev device to map into the address space of an
+ *      application running in Y. This is the first point at which Xen does any
+ *      tracking of the page.
+ *   5. A program in X mmap()s a segment of the gntalloc device that 
corresponds
+ *      to the shared page, and can now communicate with Y over the shared 
page.
+ *
+ *
+ * NOTE TO USERSPACE LIBRARIES:
+ *   The grant allocation and mmap()ing are, naturally, two separate 
operations.
+ *   You set up the sharing by calling the create ioctl() and then the mmap().
+ *   Teardown requires munmap() and either close() or ioctl().
+ *
+ * WARNING: Since Xen does not allow a guest to forcibly end the use of a grant
+ * reference, this device can be used to consume kernel memory by leaving grant
+ * references mapped by another domain when an application exits. Therefore,
+ * there is a global limit on the number of pages that can be allocated. When
+ * all references to the page are unmapped, it will be freed during the next
+ * grant operation.
+ */
+
+#include <linux/atomic.h>
+#include <linux/module.h>
+#include <linux/miscdevice.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/device.h>
+#include <linux/mm.h>
+#include <linux/uaccess.h>
+#include <linux/types.h>
+#include <linux/list.h>
+
+#include <xen/xen.h>
+#include <xen/page.h>
+#include <xen/grant_table.h>
+#include <xen/gntalloc.h>
+
+static int limit = 1024;
+module_param(limit, int, 0644);
+MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
+               "the gntalloc device");
+
+static LIST_HEAD(gref_list);
+static DEFINE_SPINLOCK(gref_lock);
+static int gref_size;
+
+/* Metadata on a grant reference. */
+struct gntalloc_gref {
+       struct list_head next_gref;  /* list entry gref_list */
+       struct list_head next_file;  /* list entry file->list, if open */
+       struct page *page;           /* The shared page */
+       uint64_t file_index;         /* File offset for mmap() */
+       unsigned int users;          /* Use count - when zero, waiting on Xen */
+       grant_ref_t gref_id;         /* The grant reference number */
+};
+
+struct gntalloc_file_private_data {
+       struct list_head list;
+       uint64_t index;
+};
+
+static void __del_gref(struct gntalloc_gref *gref);
+
+static void do_cleanup(void)
+{
+       struct gntalloc_gref *gref, *n;
+       list_for_each_entry_safe(gref, n, &gref_list, next_gref) {
+               if (!gref->users)
+                       __del_gref(gref);
+       }
+}
+
+static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
+       uint32_t *gref_ids, struct gntalloc_file_private_data *priv)
+{
+       int i, rc, readonly;
+       LIST_HEAD(queue_gref);
+       LIST_HEAD(queue_file);
+       struct gntalloc_gref *gref;
+
+       readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
+       rc = -ENOMEM;
+       for (i = 0; i < op->count; i++) {
+               gref = kzalloc(sizeof(*gref), GFP_KERNEL);
+               if (!gref)
+                       goto undo;
+               list_add_tail(&gref->next_gref, &queue_gref);
+               list_add_tail(&gref->next_file, &queue_file);
+               gref->users = 1;
+               gref->file_index = op->index + i * PAGE_SIZE;
+               gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
+               if (!gref->page)
+                       goto undo;
+
+               /* Grant foreign access to the page. */
+               gref->gref_id = gnttab_grant_foreign_access(op->domid,
+                       pfn_to_mfn(page_to_pfn(gref->page)), readonly);
+               if (gref->gref_id < 0) {
+                       rc = gref->gref_id;
+                       goto undo;
+               }
+               gref_ids[i] = gref->gref_id;
+       }
+
+       /* Add to gref lists. */
+       spin_lock(&gref_lock);
+       list_splice_tail(&queue_gref, &gref_list);
+       list_splice_tail(&queue_file, &priv->list);
+       spin_unlock(&gref_lock);
+
+       return 0;
+
+undo:
+       spin_lock(&gref_lock);
+       gref_size -= (op->count - i);
+
+       list_for_each_entry(gref, &queue_file, next_file) {
+               /* __del_gref does not remove from queue_file */
+               __del_gref(gref);
+       }
+
+       /* It's possible for the target domain to map the just-allocated grant
+        * references by blindly guessing their IDs; if this is done, then
+        * __del_gref will leave them in the queue_gref list. They need to be
+        * added to the global list so that we can free them when they are no
+        * longer referenced.
+        */
+       if (unlikely(!list_empty(&queue_gref)))
+               list_splice_tail(&queue_gref, &gref_list);
+       spin_unlock(&gref_lock);
+       return rc;
+}
+
+static void __del_gref(struct gntalloc_gref *gref)
+{
+       if (gref->gref_id > 0) {
+               if (gnttab_query_foreign_access(gref->gref_id))
+                       return;
+
+               if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
+                       return;
+       }
+
+       gref_size--;
+       list_del(&gref->next_gref);
+
+       if (gref->page)
+               __free_page(gref->page);
+
+       kfree(gref);
+}
+
+/* finds contiguous grant references in a file, returns the first */
+static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data 
*priv,
+               uint64_t index, uint32_t count)
+{
+       struct gntalloc_gref *rv = NULL, *gref;
+       list_for_each_entry(gref, &priv->list, next_file) {
+               if (gref->file_index == index && !rv)
+                       rv = gref;
+               if (rv) {
+                       if (gref->file_index != index)
+                               return NULL;
+                       index += PAGE_SIZE;
+                       count--;
+                       if (count == 0)
+                               return rv;
+               }
+       }
+       return NULL;
+}
+
+/*
+ * -------------------------------------
+ *  File operations.
+ * -------------------------------------
+ */
+static int gntalloc_open(struct inode *inode, struct file *filp)
+{
+       struct gntalloc_file_private_data *priv;
+
+       priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+       if (!priv)
+               goto out_nomem;
+       INIT_LIST_HEAD(&priv->list);
+
+       filp->private_data = priv;
+
+       pr_debug("%s: priv %p\n", __func__, priv);
+
+       return 0;
+
+out_nomem:
+       return -ENOMEM;
+}
+
+static int gntalloc_release(struct inode *inode, struct file *filp)
+{
+       struct gntalloc_file_private_data *priv = filp->private_data;
+       struct gntalloc_gref *gref;
+
+       pr_debug("%s: priv %p\n", __func__, priv);
+
+       spin_lock(&gref_lock);
+       while (!list_empty(&priv->list)) {
+               gref = list_entry(priv->list.next,
+                       struct gntalloc_gref, next_file);
+               list_del(&gref->next_file);
+               gref->users--;
+               if (gref->users == 0)
+                       __del_gref(gref);
+       }
+       kfree(priv);
+       spin_unlock(&gref_lock);
+
+       return 0;
+}
+
+static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
+               struct ioctl_gntalloc_alloc_gref __user *arg)
+{
+       int rc = 0;
+       struct ioctl_gntalloc_alloc_gref op;
+       uint32_t *gref_ids;
+
+       pr_debug("%s: priv %p\n", __func__, priv);
+
+       if (copy_from_user(&op, arg, sizeof(op))) {
+               rc = -EFAULT;
+               goto out;
+       }
+
+       gref_ids = kzalloc(sizeof(gref_ids[0]) * op.count, GFP_TEMPORARY);
+       if (!gref_ids) {
+               rc = -ENOMEM;
+               goto out;
+       }
+
+       spin_lock(&gref_lock);
+       /* Clean up pages that were at zero (local) users but were still mapped
+        * by remote domains. Since those pages count towards the limit that we
+        * are about to enforce, removing them here is a good idea.
+        */
+       do_cleanup();
+       if (gref_size + op.count > limit) {
+               spin_unlock(&gref_lock);
+               rc = -ENOSPC;
+               goto out_free;
+       }
+       gref_size += op.count;
+       op.index = priv->index;
+       priv->index += op.count * PAGE_SIZE;
+       spin_unlock(&gref_lock);
+
+       rc = add_grefs(&op, gref_ids, priv);
+       if (rc < 0)
+               goto out_free;
+
+       /* Once we finish add_grefs, it is unsafe to touch the new reference,
+        * since it is possible for a concurrent ioctl to remove it (by guessing
+        * its index). If the userspace application doesn't provide valid memory
+        * to write the IDs to, then it will need to close the file in order to
+        * release - which it will do by segfaulting when it tries to access the
+        * IDs to close them.
+        */
+       if (copy_to_user(arg, &op, sizeof(op))) {
+               rc = -EFAULT;
+               goto out_free;
+       }
+       if (copy_to_user(arg->gref_ids, gref_ids,
+                       sizeof(gref_ids[0]) * op.count)) {
+               rc = -EFAULT;
+               goto out_free;
+       }
+
+out_free:
+       kfree(gref_ids);
+out:
+       return rc;
+}
+
+static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
+               void __user *arg)
+{
+       int i, rc = 0;
+       struct ioctl_gntalloc_dealloc_gref op;
+       struct gntalloc_gref *gref, *n;
+
+       pr_debug("%s: priv %p\n", __func__, priv);
+
+       if (copy_from_user(&op, arg, sizeof(op))) {
+               rc = -EFAULT;
+               goto dealloc_grant_out;
+       }
+
+       spin_lock(&gref_lock);
+       gref = find_grefs(priv, op.index, op.count);
+       if (gref) {
+               /* Remove from the file list only, and decrease reference count.
+                * The later call to do_cleanup() will remove from gref_list and
+                * free the memory if the pages aren't mapped anywhere.
+                */
+               for (i = 0; i < op.count; i++) {
+                       n = list_entry(gref->next_file.next,
+                               struct gntalloc_gref, next_file);
+                       list_del(&gref->next_file);
+                       gref->users--;
+                       gref = n;
+               }
+       } else {
+               rc = -EINVAL;
+       }
+
+       do_cleanup();
+
+       spin_unlock(&gref_lock);
+dealloc_grant_out:
+       return rc;
+}
+
+static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
+               unsigned long arg)
+{
+       struct gntalloc_file_private_data *priv = filp->private_data;
+
+       switch (cmd) {
+       case IOCTL_GNTALLOC_ALLOC_GREF:
+               return gntalloc_ioctl_alloc(priv, (void __user *)arg);
+
+       case IOCTL_GNTALLOC_DEALLOC_GREF:
+               return gntalloc_ioctl_dealloc(priv, (void __user *)arg);
+
+       default:
+               return -ENOIOCTLCMD;
+       }
+
+       return 0;
+}
+
+static void gntalloc_vma_close(struct vm_area_struct *vma)
+{
+       struct gntalloc_gref *gref = vma->vm_private_data;
+       if (!gref)
+               return;
+
+       spin_lock(&gref_lock);
+       gref->users--;
+       if (gref->users == 0)
+               __del_gref(gref);
+       spin_unlock(&gref_lock);
+}
+
+static struct vm_operations_struct gntalloc_vmops = {
+       .close = gntalloc_vma_close,
+};
+
+static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+       struct gntalloc_file_private_data *priv = filp->private_data;
+       struct gntalloc_gref *gref;
+       int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+       int rv, i;
+
+       pr_debug("%s: priv %p, page %lu+%d\n", __func__,
+                      priv, vma->vm_pgoff, count);
+
+       if (!(vma->vm_flags & VM_SHARED)) {
+               printk(KERN_ERR "%s: Mapping must be shared.\n", __func__);
+               return -EINVAL;
+       }
+
+       spin_lock(&gref_lock);
+       gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
+       if (gref == NULL) {
+               rv = -ENOENT;
+               pr_debug("%s: Could not find grant reference",
+                               __func__);
+               goto out_unlock;
+       }
+
+       vma->vm_private_data = gref;
+
+       vma->vm_flags |= VM_RESERVED;
+       vma->vm_flags |= VM_DONTCOPY;
+       vma->vm_flags |= VM_PFNMAP | VM_PFN_AT_MMAP;
+
+       vma->vm_ops = &gntalloc_vmops;
+
+       for (i = 0; i < count; i++) {
+               gref->users++;
+               rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
+                               gref->page);
+               if (rv)
+                       goto out_unlock;
+
+               gref = list_entry(gref->next_file.next,
+                               struct gntalloc_gref, next_file);
+       }
+       rv = 0;
+
+out_unlock:
+       spin_unlock(&gref_lock);
+       return rv;
+}
+
+static const struct file_operations gntalloc_fops = {
+       .owner = THIS_MODULE,
+       .open = gntalloc_open,
+       .release = gntalloc_release,
+       .unlocked_ioctl = gntalloc_ioctl,
+       .mmap = gntalloc_mmap
+};
+
+/*
+ * -------------------------------------
+ * Module creation/destruction.
+ * -------------------------------------
+ */
+static struct miscdevice gntalloc_miscdev = {
+       .minor  = MISC_DYNAMIC_MINOR,
+       .name   = "xen/gntalloc",
+       .fops   = &gntalloc_fops,
+};
+
+static int __init gntalloc_init(void)
+{
+       int err;
+
+       if (!xen_domain())
+               return -ENODEV;
+
+       err = misc_register(&gntalloc_miscdev);
+       if (err != 0) {
+               printk(KERN_ERR "Could not register misc gntalloc device\n");
+               return err;
+       }
+
+       pr_debug("Created grant allocation device at %d,%d\n",
+                       MISC_MAJOR, gntalloc_miscdev.minor);
+
+       return 0;
+}
+
+static void __exit gntalloc_exit(void)
+{
+       misc_deregister(&gntalloc_miscdev);
+}
+
+module_init(gntalloc_init);
+module_exit(gntalloc_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Carter Weatherly <carter.weatherly@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..bc3b85e
--- /dev/null
+++ b/include/xen/gntalloc.h
@@ -0,0 +1,50 @@
+/******************************************************************************
+ * gntalloc.h
+ *
+ * Interface to /dev/xen/gntalloc.
+ *
+ * Author: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
+ *
+ * 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__ */
-- 
1.7.3.4


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