[PATCH 1/7] vfio: Create vfio_fs_type with inode per device

Alex Williamson
2021-08-05T17:07:25Z

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 <jgg@nvidia.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
drivers/vfio/vfio.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/vfio.h | 1 +
2 files changed, 58 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 02cc51ce6891..b88de89bda31 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -21,8 +21,10 @@
#include <linux/list.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
+#include <linux/mount.h>
#include <linux/mutex.h>
#include <linux/pci.h>
+#include <linux/pseudo_fs.h>
#include <linux/rwsem.h>
#include <linux/sched.h>
#include <linux/slab.h>
@@ -37,6 +39,14 @@
#define DRIVER_AUTHOR "Alex Williamson <alex.williamson@redhat.com>"
#define DRIVER_DESC "VFIO - User Level meta-driver"

+/*
+ * Not exposed via UAPI
+ *
+ * XXX Adopt the following when available:
+ * https://lore.kernel.org/lkml/20210309155348.974875-1-hch@lst.de/
+ */
+#define VFIO_MAGIC 0x5646494f /* "VFIO" */
+
static struct vfio {
struct class *class;
struct list_head iommu_drivers_list;
@@ -46,6 +56,8 @@ static struct vfio {
struct mutex group_lock;
struct cdev group_cdev;
dev_t group_devt;
+ struct vfsmount *vfio_fs_mnt;
+ int vfio_fs_cnt;
} vfio;

struct vfio_iommu_driver {
@@ -519,6 +531,35 @@ 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.vfio_fs_mnt, &vfio.vfio_fs_cnt);
+ if (ret)
+ return ERR_PTR(ret);
+
+ inode = alloc_anon_inode(vfio.vfio_fs_mnt->mnt_sb);
+ if (IS_ERR(inode))
+ simple_release_fs(&vfio.vfio_fs_mnt, &vfio.vfio_fs_cnt);
+
+ return inode;
+}
+
/**
* Device objects - create, release, get, put, search
*/
@@ -783,6 +824,12 @@ int vfio_register_group_dev(struct vfio_device *device)
return -EBUSY;
}

+ device->inode = vfio_fs_inode_new();
+ if (IS_ERR(device->inode)) {
+ vfio_group_put(group);
+ return PTR_ERR(device->inode);
+ }
+
/* Our reference on group is moved to the device */
device->group = group;

@@ -907,6 +954,9 @@ void vfio_unregister_group_dev(struct vfio_device *device)
group->dev_counter--;
mutex_unlock(&group->device_lock);

+ iput(device->inode);
+ simple_release_fs(&vfio.vfio_fs_mnt, &vfio.vfio_fs_cnt);
+
/*
* In order to support multiple devices per group, devices can be
* plucked from the group while other devices in the group are still
@@ -1411,6 +1461,13 @@ 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);
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index a2c5b30e1763..90bcc2e9c8eb 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -24,6 +24,7 @@ struct vfio_device {
refcount_t refcount;
struct completion comp;
struct list_head group_next;
+ struct inode *inode;
};

/**