[PATCH v1 01/14] vfio: Create vfio_fs_type with inode per device

[Alex Williamson]

By linking all the device fds we provide to userspace to an
address space through a new pseudo fs, we can use tools like
unmap_mapping_range() to zap all vmas associated with a device.

Suggested-by: Jason Gunthorpe <j...@nvidia.com>
Signed-off-by: Alex Williamson <alex.william...@redhat.com>
---
 drivers/vfio/vfio.c |   54 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 38779e6fd80c..abdf8d52a911 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -32,11 +32,18 @@
 #include <linux/vfio.h>
 #include <linux/wait.h>
 #include <linux/sched/signal.h>
+#include <linux/pseudo_fs.h>
+#include <linux/mount.h>
 
 #define DRIVER_VERSION "0.3"
 #define DRIVER_AUTHOR  "Alex Williamson <alex.william...@redhat.com>"
 #define DRIVER_DESC    "VFIO - User Level meta-driver"
 
+#define VFIO_MAGIC 0x5646494f /* "VFIO" */
+
+static int vfio_fs_cnt;
+static struct vfsmount *vfio_fs_mnt;
+
 static struct vfio {
        struct class                    *class;
        struct list_head                iommu_drivers_list;
@@ -97,6 +104,7 @@ struct vfio_device {
        struct vfio_group               *group;
        struct list_head                group_next;
        void                            *device_data;
+       struct inode                    *inode;
 };
 
 #ifdef CONFIG_VFIO_NOIOMMU
@@ -529,6 +537,34 @@ static struct vfio_group *vfio_group_get_from_dev(struct 
device *dev)
        return group;
 }
 
+static int vfio_fs_init_fs_context(struct fs_context *fc)
+{
+       return init_pseudo(fc, VFIO_MAGIC) ? 0 : -ENOMEM;
+}
+
+static struct file_system_type vfio_fs_type = {
+       .name = "vfio",
+       .owner = THIS_MODULE,
+       .init_fs_context = vfio_fs_init_fs_context,
+       .kill_sb = kill_anon_super,
+};
+
+static struct inode *vfio_fs_inode_new(void)
+{
+       struct inode *inode;
+       int ret;
+
+       ret = simple_pin_fs(&vfio_fs_type, &vfio_fs_mnt, &vfio_fs_cnt);
+       if (ret)
+               return ERR_PTR(ret);
+
+       inode = alloc_anon_inode(vfio_fs_mnt->mnt_sb);
+       if (IS_ERR(inode))
+               simple_release_fs(&vfio_fs_mnt, &vfio_fs_cnt);
+
+       return inode;
+}
+
 /**
  * Device objects - create, release, get, put, search
  */
@@ -539,11 +575,19 @@ struct vfio_device *vfio_group_create_device(struct 
vfio_group *group,
                                             void *device_data)
 {
        struct vfio_device *device;
+       struct inode *inode;
 
        device = kzalloc(sizeof(*device), GFP_KERNEL);
        if (!device)
                return ERR_PTR(-ENOMEM);
 
+       inode = vfio_fs_inode_new();
+       if (IS_ERR(inode)) {
+               kfree(device);
+               return ERR_CAST(inode);
+       }
+       device->inode = inode;
+
        kref_init(&device->kref);
        device->dev = dev;
        device->group = group;
@@ -574,6 +618,9 @@ static void vfio_device_release(struct kref *kref)
 
        dev_set_drvdata(device->dev, NULL);
 
+       iput(device->inode);
+       simple_release_fs(&vfio_fs_mnt, &vfio_fs_cnt);
+
        kfree(device);
 
        /* vfio_del_group_dev may be waiting for this device */
@@ -1488,6 +1535,13 @@ static int vfio_group_get_device_fd(struct vfio_group 
*group, char *buf)
         */
        filep->f_mode |= (FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE);
 
+       /*
+        * Use the pseudo fs inode on the device to link all mmaps
+        * to the same address space, allowing us to unmap all vmas
+        * associated to this device using unmap_mapping_range().
+        */
+       filep->f_mapping = device->inode->i_mapping;
+
        atomic_inc(&group->container_users);
 
        fd_install(ret, filep);