xen/gntdev: allow usermode to map granted pages

The gntdev driver allows usermode to map granted pages from other
domains.  This is typically used to implement a Xen backend driver
in user mode.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

3 files changed, 644 insertions, 0 deletions

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 6e6180ccd726..bd3095f0dff2 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -62,6 +62,13 @@ config XEN_SYS_HYPERVISOR
          virtual environment, /sys/hypervisor will still be present,
          but will have no xen contents.
 
+config XEN_GNTDEV
+        tristate "userspace grant access device driver"
+        depends on XEN
+        select MMU_NOTIFIER
+        help
+          Allows userspace processes to use grants.
+
 config XEN_PLATFORM_PCI
         tristate "xen platform pci device driver"
         depends on XEN_PVHVM
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 533a199e7a3f..674fdb5fee49 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_HOTPLUG_CPU)	+= cpu_hotplug.o
 obj-$(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_XENFS)             += xenfs/
 obj-$(CONFIG_XEN_SYS_HYPERVISOR)        += sys-hypervisor.o
 obj-$(CONFIG_XEN_PLATFORM_PCI)  += platform-pci.o
@@ -16,4 +17,5 @@ obj-$(CONFIG_SWIOTLB_XEN)	+= swiotlb-xen.o
 obj-$(CONFIG_XEN_DOM0)          += pci.o
 
 xen-evtchn-y                    := evtchn.o
+xen-gntdev-y                            := gntdev.o
 
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
new file mode 100644
index 000000000000..cfe063372aa4
--- /dev/null
+++ b/drivers/xen/gntdev.c
@@ -0,0 +1,635 @@
+/******************************************************************************
+ * gntdev.c
+ *
+ * Device for accessing (in user-space) pages that have been granted by other
+ * domains.
+ *
+ * Copyright (c) 2006-2007, D G Murray.
+ *           (c) 2009 Gerd Hoffmann <kraxel@redhat.com>
+ *
+ * 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
+ */
+
+#undef DEBUG
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/miscdevice.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/mmu_notifier.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/slab.h>
+
+#include <xen/xen.h>
+#include <xen/grant_table.h>
+#include <xen/gntdev.h>
+#include <asm/xen/hypervisor.h>
+#include <asm/xen/hypercall.h>
+#include <asm/xen/page.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Derek G. Murray <Derek.Murray@cl.cam.ac.uk>, "
+              "Gerd Hoffmann <kraxel@redhat.com>");
+MODULE_DESCRIPTION("User-space granted page access driver");
+
+static int limit = 1024;
+module_param(limit, int, 0644);
+MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped at "
+                "once by a gntdev instance");
+
+struct gntdev_priv {
+        struct list_head maps;
+        uint32_t used;
+        uint32_t limit;
+        /* lock protects maps from concurrent changes */
+        spinlock_t lock;
+        struct mm_struct *mm;
+        struct mmu_notifier mn;
+};
+
+struct grant_map {
+        struct list_head next;
+        struct gntdev_priv *priv;
+        struct vm_area_struct *vma;
+        int index;
+        int count;
+        int flags;
+        int is_mapped;
+        struct ioctl_gntdev_grant_ref *grants;
+        struct gnttab_map_grant_ref   *map_ops;
+        struct gnttab_unmap_grant_ref *unmap_ops;
+};
+
+/* ------------------------------------------------------------------ */
+
+static void gntdev_print_maps(struct gntdev_priv *priv,
+                              char *text, int text_index)
+{
+#ifdef DEBUG
+        struct grant_map *map;
+
+        pr_debug("maps list (priv %p, usage %d/%d)\n",
+               priv, priv->used, priv->limit);
+
+        list_for_each_entry(map, &priv->maps, next)
+                pr_debug("  index %2d, count %2d %s\n",
+                       map->index, map->count,
+                       map->index == text_index && text ? text : "");
+#endif
+}
+
+static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
+{
+        struct grant_map *add;
+
+        add = kzalloc(sizeof(struct grant_map), GFP_KERNEL);
+        if (NULL == add)
+                return NULL;
+
+        add->grants    = kzalloc(sizeof(add->grants[0])    * count, GFP_KERNEL);
+        add->map_ops   = kzalloc(sizeof(add->map_ops[0])   * count, GFP_KERNEL);
+        add->unmap_ops = kzalloc(sizeof(add->unmap_ops[0]) * count, GFP_KERNEL);
+        if (NULL == add->grants  ||
+            NULL == add->map_ops ||
+            NULL == add->unmap_ops)
+                goto err;
+
+        add->index = 0;
+        add->count = count;
+        add->priv  = priv;
+
+        if (add->count + priv->used > priv->limit)
+                goto err;
+
+        return add;
+
+err:
+        kfree(add->grants);
+        kfree(add->map_ops);
+        kfree(add->unmap_ops);
+        kfree(add);
+        return NULL;
+}
+
+static void gntdev_add_map(struct gntdev_priv *priv, struct grant_map *add)
+{
+        struct grant_map *map;
+
+        list_for_each_entry(map, &priv->maps, next) {
+                if (add->index + add->count < map->index) {
+                        list_add_tail(&add->next, &map->next);
+                        goto done;
+                }
+                add->index = map->index + map->count;
+        }
+        list_add_tail(&add->next, &priv->maps);
+
+done:
+        priv->used += add->count;
+        gntdev_print_maps(priv, "[new]", add->index);
+}
+
+static struct grant_map *gntdev_find_map_index(struct gntdev_priv *priv,
+                int index, int count)
+{
+        struct grant_map *map;
+
+        list_for_each_entry(map, &priv->maps, next) {
+                if (map->index != index)
+                        continue;
+                if (map->count != count)
+                        continue;
+                return map;
+        }
+        return NULL;
+}
+
+static struct grant_map *gntdev_find_map_vaddr(struct gntdev_priv *priv,
+                                               unsigned long vaddr)
+{
+        struct grant_map *map;
+
+        list_for_each_entry(map, &priv->maps, next) {
+                if (!map->vma)
+                        continue;
+                if (vaddr < map->vma->vm_start)
+                        continue;
+                if (vaddr >= map->vma->vm_end)
+                        continue;
+                return map;
+        }
+        return NULL;
+}
+
+static int gntdev_del_map(struct grant_map *map)
+{
+        int i;
+
+        if (map->vma)
+                return -EBUSY;
+        for (i = 0; i < map->count; i++)
+                if (map->unmap_ops[i].handle)
+                        return -EBUSY;
+
+        map->priv->used -= map->count;
+        list_del(&map->next);
+        return 0;
+}
+
+static void gntdev_free_map(struct grant_map *map)
+{
+        if (!map)
+                return;
+        kfree(map->grants);
+        kfree(map->map_ops);
+        kfree(map->unmap_ops);
+        kfree(map);
+}
+
+/* ------------------------------------------------------------------ */
+
+static int find_grant_ptes(pte_t *pte, pgtable_t token,
+                unsigned long addr, void *data)
+{
+        struct grant_map *map = data;
+        unsigned int pgnr = (addr - map->vma->vm_start) >> PAGE_SHIFT;
+        u64 pte_maddr;
+
+        BUG_ON(pgnr >= map->count);
+        pte_maddr  = (u64)pfn_to_mfn(page_to_pfn(token)) << PAGE_SHIFT;
+        pte_maddr += (unsigned long)pte & ~PAGE_MASK;
+        gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr, map->flags,
+                          map->grants[pgnr].ref,
+                          map->grants[pgnr].domid);
+        gnttab_set_unmap_op(&map->unmap_ops[pgnr], pte_maddr, map->flags,
+                            0 /* handle */);
+        return 0;
+}
+
+static int map_grant_pages(struct grant_map *map)
+{
+        int i, err = 0;
+
+        pr_debug("map %d+%d\n", map->index, map->count);
+        err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
+                                        map->map_ops, map->count);
+        if (err)
+                return err;
+
+        for (i = 0; i < map->count; i++) {
+                if (map->map_ops[i].status)
+                        err = -EINVAL;
+                map->unmap_ops[i].handle = map->map_ops[i].handle;
+        }
+        return err;
+}
+
+static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
+{
+        int i, err = 0;
+
+        pr_debug("map %d+%d [%d+%d]\n", map->index, map->count, offset, pages);
+        err = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
+                                        map->unmap_ops + offset, pages);
+        if (err)
+                return err;
+
+        for (i = 0; i < pages; i++) {
+                if (map->unmap_ops[offset+i].status)
+                        err = -EINVAL;
+                map->unmap_ops[offset+i].handle = 0;
+        }
+        return err;
+}
+
+/* ------------------------------------------------------------------ */
+
+static void gntdev_vma_close(struct vm_area_struct *vma)
+{
+        struct grant_map *map = vma->vm_private_data;
+
+        pr_debug("close %p\n", vma);
+        map->is_mapped = 0;
+        map->vma = NULL;
+        vma->vm_private_data = NULL;
+}
+
+static int gntdev_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+        pr_debug("vaddr %p, pgoff %ld (shouldn't happen)\n",
+                        vmf->virtual_address, vmf->pgoff);
+        vmf->flags = VM_FAULT_ERROR;
+        return 0;
+}
+
+static struct vm_operations_struct gntdev_vmops = {
+        .close = gntdev_vma_close,
+        .fault = gntdev_vma_fault,
+};
+
+/* ------------------------------------------------------------------ */
+
+static void mn_invl_range_start(struct mmu_notifier *mn,
+                                struct mm_struct *mm,
+                                unsigned long start, unsigned long end)
+{
+        struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
+        struct grant_map *map;
+        unsigned long mstart, mend;
+        int err;
+
+        spin_lock(&priv->lock);
+        list_for_each_entry(map, &priv->maps, next) {
+                if (!map->vma)
+                        continue;
+                if (!map->is_mapped)
+                        continue;
+                if (map->vma->vm_start >= end)
+                        continue;
+                if (map->vma->vm_end <= start)
+                        continue;
+                mstart = max(start, map->vma->vm_start);
+                mend   = min(end,   map->vma->vm_end);
+                pr_debug("map %d+%d (%lx %lx), range %lx %lx, mrange %lx %lx\n",
+                                map->index, map->count,
+                                map->vma->vm_start, map->vma->vm_end,
+                                start, end, mstart, mend);
+                err = unmap_grant_pages(map,
+                                        (mstart - map->vma->vm_start) >> PAGE_SHIFT,
+                                        (mend - mstart) >> PAGE_SHIFT);
+                WARN_ON(err);
+        }
+        spin_unlock(&priv->lock);
+}
+
+static void mn_invl_page(struct mmu_notifier *mn,
+                         struct mm_struct *mm,
+                         unsigned long address)
+{
+        mn_invl_range_start(mn, mm, address, address + PAGE_SIZE);
+}
+
+static void mn_release(struct mmu_notifier *mn,
+                       struct mm_struct *mm)
+{
+        struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
+        struct grant_map *map;
+        int err;
+
+        spin_lock(&priv->lock);
+        list_for_each_entry(map, &priv->maps, next) {
+                if (!map->vma)
+                        continue;
+                pr_debug("map %d+%d (%lx %lx)\n",
+                                map->index, map->count,
+                                map->vma->vm_start, map->vma->vm_end);
+                err = unmap_grant_pages(map, /* offset */ 0, map->count);
+                WARN_ON(err);
+        }
+        spin_unlock(&priv->lock);
+}
+
+struct mmu_notifier_ops gntdev_mmu_ops = {
+        .release                = mn_release,
+        .invalidate_page        = mn_invl_page,
+        .invalidate_range_start = mn_invl_range_start,
+};
+
+/* ------------------------------------------------------------------ */
+
+static int gntdev_open(struct inode *inode, struct file *flip)
+{
+        struct gntdev_priv *priv;
+        int ret = 0;
+
+        priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+        if (!priv)
+                return -ENOMEM;
+
+        INIT_LIST_HEAD(&priv->maps);
+        spin_lock_init(&priv->lock);
+        priv->limit = limit;
+
+        priv->mm = get_task_mm(current);
+        if (!priv->mm) {
+                kfree(priv);
+                return -ENOMEM;
+        }
+        priv->mn.ops = &gntdev_mmu_ops;
+        ret = mmu_notifier_register(&priv->mn, priv->mm);
+        mmput(priv->mm);
+
+        if (ret) {
+                kfree(priv);
+                return ret;
+        }
+
+        flip->private_data = priv;
+        pr_debug("priv %p\n", priv);
+
+        return 0;
+}
+
+static int gntdev_release(struct inode *inode, struct file *flip)
+{
+        struct gntdev_priv *priv = flip->private_data;
+        struct grant_map *map;
+        int err;
+
+        pr_debug("priv %p\n", priv);
+
+        spin_lock(&priv->lock);
+        while (!list_empty(&priv->maps)) {
+                map = list_entry(priv->maps.next, struct grant_map, next);
+                err = gntdev_del_map(map);
+                if (WARN_ON(err))
+                        gntdev_free_map(map);
+
+        }
+        spin_unlock(&priv->lock);
+
+        mmu_notifier_unregister(&priv->mn, priv->mm);
+        kfree(priv);
+        return 0;
+}
+
+static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv,
+                                       struct ioctl_gntdev_map_grant_ref __user *u)
+{
+        struct ioctl_gntdev_map_grant_ref op;
+        struct grant_map *map;
+        int err;
+
+        if (copy_from_user(&op, u, sizeof(op)) != 0)
+                return -EFAULT;
+        pr_debug("priv %p, add %d\n", priv, op.count);
+        if (unlikely(op.count <= 0))
+                return -EINVAL;
+        if (unlikely(op.count > priv->limit))
+                return -EINVAL;
+
+        err = -ENOMEM;
+        map = gntdev_alloc_map(priv, op.count);
+        if (!map)
+                return err;
+        if (copy_from_user(map->grants, &u->refs,
+                           sizeof(map->grants[0]) * op.count) != 0) {
+                gntdev_free_map(map);
+                return err;
+        }
+
+        spin_lock(&priv->lock);
+        gntdev_add_map(priv, map);
+        op.index = map->index << PAGE_SHIFT;
+        spin_unlock(&priv->lock);
+
+        if (copy_to_user(u, &op, sizeof(op)) != 0) {
+                spin_lock(&priv->lock);
+                gntdev_del_map(map);
+                spin_unlock(&priv->lock);
+                gntdev_free_map(map);
+                return err;
+        }
+        return 0;
+}
+
+static long gntdev_ioctl_unmap_grant_ref(struct gntdev_priv *priv,
+                                         struct ioctl_gntdev_unmap_grant_ref __user *u)
+{
+        struct ioctl_gntdev_unmap_grant_ref op;
+        struct grant_map *map;
+        int err = -ENOENT;
+
+        if (copy_from_user(&op, u, sizeof(op)) != 0)
+                return -EFAULT;
+        pr_debug("priv %p, del %d+%d\n", priv, (int)op.index, (int)op.count);
+
+        spin_lock(&priv->lock);
+        map = gntdev_find_map_index(priv, op.index >> PAGE_SHIFT, op.count);
+        if (map)
+                err = gntdev_del_map(map);
+        spin_unlock(&priv->lock);
+        if (!err)
+                gntdev_free_map(map);
+        return err;
+}
+
+static long gntdev_ioctl_get_offset_for_vaddr(struct gntdev_priv *priv,
+                                              struct ioctl_gntdev_get_offset_for_vaddr __user *u)
+{
+        struct ioctl_gntdev_get_offset_for_vaddr op;
+        struct grant_map *map;
+
+        if (copy_from_user(&op, u, sizeof(op)) != 0)
+                return -EFAULT;
+        pr_debug("priv %p, offset for vaddr %lx\n", priv, (unsigned long)op.vaddr);
+
+        spin_lock(&priv->lock);
+        map = gntdev_find_map_vaddr(priv, op.vaddr);
+        if (map == NULL ||
+            map->vma->vm_start != op.vaddr) {
+                spin_unlock(&priv->lock);
+                return -EINVAL;
+        }
+        op.offset = map->index << PAGE_SHIFT;
+        op.count = map->count;
+        spin_unlock(&priv->lock);
+
+        if (copy_to_user(u, &op, sizeof(op)) != 0)
+                return -EFAULT;
+        return 0;
+}
+
+static long gntdev_ioctl_set_max_grants(struct gntdev_priv *priv,
+                                        struct ioctl_gntdev_set_max_grants __user *u)
+{
+        struct ioctl_gntdev_set_max_grants op;
+
+        if (copy_from_user(&op, u, sizeof(op)) != 0)
+                return -EFAULT;
+        pr_debug("priv %p, limit %d\n", priv, op.count);
+        if (op.count > limit)
+                return -E2BIG;
+
+        spin_lock(&priv->lock);
+        priv->limit = op.count;
+        spin_unlock(&priv->lock);
+        return 0;
+}
+
+static long gntdev_ioctl(struct file *flip,
+                         unsigned int cmd, unsigned long arg)
+{
+        struct gntdev_priv *priv = flip->private_data;
+        void __user *ptr = (void __user *)arg;
+
+        switch (cmd) {
+        case IOCTL_GNTDEV_MAP_GRANT_REF:
+                return gntdev_ioctl_map_grant_ref(priv, ptr);
+
+        case IOCTL_GNTDEV_UNMAP_GRANT_REF:
+                return gntdev_ioctl_unmap_grant_ref(priv, ptr);
+
+        case IOCTL_GNTDEV_GET_OFFSET_FOR_VADDR:
+                return gntdev_ioctl_get_offset_for_vaddr(priv, ptr);
+
+        case IOCTL_GNTDEV_SET_MAX_GRANTS:
+                return gntdev_ioctl_set_max_grants(priv, ptr);
+
+        default:
+                pr_debug("priv %p, unknown cmd %x\n", priv, cmd);
+                return -ENOIOCTLCMD;
+        }
+
+        return 0;
+}
+
+static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
+{
+        struct gntdev_priv *priv = flip->private_data;
+        int index = vma->vm_pgoff;
+        int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+        struct grant_map *map;
+        int err = -EINVAL;
+
+        if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
+                return -EINVAL;
+
+        pr_debug("map %d+%d at %lx (pgoff %lx)\n",
+                        index, count, vma->vm_start, vma->vm_pgoff);
+
+        spin_lock(&priv->lock);
+        map = gntdev_find_map_index(priv, index, count);
+        if (!map)
+                goto unlock_out;
+        if (map->vma)
+                goto unlock_out;
+        if (priv->mm != vma->vm_mm) {
+                printk(KERN_WARNING "Huh? Other mm?\n");
+                goto unlock_out;
+        }
+
+        vma->vm_ops = &gntdev_vmops;
+
+        vma->vm_flags |= VM_RESERVED|VM_DONTCOPY|VM_DONTEXPAND;
+
+        vma->vm_private_data = map;
+        map->vma = vma;
+
+        map->flags = GNTMAP_host_map | GNTMAP_application_map | GNTMAP_contains_pte;
+        if (!(vma->vm_flags & VM_WRITE))
+                map->flags |= GNTMAP_readonly;
+
+        err = apply_to_page_range(vma->vm_mm, vma->vm_start,
+                                  vma->vm_end - vma->vm_start,
+                                  find_grant_ptes, map);
+        if (err) {
+                printk(KERN_WARNING "find_grant_ptes() failure.\n");
+                goto unlock_out;
+        }
+
+        err = map_grant_pages(map);
+        if (err) {
+                printk(KERN_WARNING "map_grant_pages() failure.\n");
+                goto unlock_out;
+        }
+        map->is_mapped = 1;
+
+unlock_out:
+        spin_unlock(&priv->lock);
+        return err;
+}
+
+static const struct file_operations gntdev_fops = {
+        .owner = THIS_MODULE,
+        .open = gntdev_open,
+        .release = gntdev_release,
+        .mmap = gntdev_mmap,
+        .unlocked_ioctl = gntdev_ioctl
+};
+
+static struct miscdevice gntdev_miscdev = {
+        .minor        = MISC_DYNAMIC_MINOR,
+        .name         = "xen/gntdev",
+        .fops         = &gntdev_fops,
+};
+
+/* ------------------------------------------------------------------ */
+
+static int __init gntdev_init(void)
+{
+        int err;
+
+        if (!xen_domain())
+                return -ENODEV;
+
+        err = misc_register(&gntdev_miscdev);
+        if (err != 0) {
+                printk(KERN_ERR "Could not register gntdev device\n");
+                return err;
+        }
+        return 0;
+}
+
+static void __exit gntdev_exit(void)
+{
+        misc_deregister(&gntdev_miscdev);
+}
+
+module_init(gntdev_init);
+module_exit(gntdev_exit);
+
+/* ------------------------------------------------------------------ */