vfio: Use down_reads to protect iommu disconnects

If a group or device is released or a container is unset from a group
it can race against file ops on the container.  Protect these with
down_reads to allow concurrent users.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reported-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 46 insertions, 16 deletions

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 073788e50e4b..ac7423bfaa7d 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -704,9 +704,13 @@ EXPORT_SYMBOL_GPL(vfio_del_group_dev);
 static long vfio_ioctl_check_extension(struct vfio_container *container,
                                        unsigned long arg)
 {
-        struct vfio_iommu_driver *driver = container->iommu_driver;
+        struct vfio_iommu_driver *driver;
         long ret = 0;
 
+        down_read(&container->group_lock);
+
+        driver = container->iommu_driver;
+
         switch (arg) {
                 /* No base extensions yet */
         default:
@@ -736,6 +740,8 @@ static long vfio_ioctl_check_extension(struct vfio_container *container,
                                                  VFIO_CHECK_EXTENSION, arg);
         }
 
+        up_read(&container->group_lock);
+
         return ret;
 }
 
@@ -844,9 +850,6 @@ static long vfio_fops_unl_ioctl(struct file *filep,
         if (!container)
                 return ret;
 
-        driver = container->iommu_driver;
-        data = container->iommu_data;
-
         switch (cmd) {
         case VFIO_GET_API_VERSION:
                 ret = VFIO_API_VERSION;
@@ -858,8 +861,15 @@ static long vfio_fops_unl_ioctl(struct file *filep,
                 ret = vfio_ioctl_set_iommu(container, arg);
                 break;
         default:
+                down_read(&container->group_lock);
+
+                driver = container->iommu_driver;
+                data = container->iommu_data;
+
                 if (driver) /* passthrough all unrecognized ioctls */
                         ret = driver->ops->ioctl(data, cmd, arg);
+
+                up_read(&container->group_lock);
         }
 
         return ret;
@@ -910,35 +920,55 @@ static ssize_t vfio_fops_read(struct file *filep, char __user *buf,
                               size_t count, loff_t *ppos)
 {
         struct vfio_container *container = filep->private_data;
-        struct vfio_iommu_driver *driver = container->iommu_driver;
+        struct vfio_iommu_driver *driver;
+        ssize_t ret = -EINVAL;
 
-        if (unlikely(!driver || !driver->ops->read))
-                return -EINVAL;
+        down_read(&container->group_lock);
+
+        driver = container->iommu_driver;
+        if (likely(driver && driver->ops->read))
+                ret = driver->ops->read(container->iommu_data,
+                                        buf, count, ppos);
 
-        return driver->ops->read(container->iommu_data, buf, count, ppos);
+        up_read(&container->group_lock);
+
+        return ret;
 }
 
 static ssize_t vfio_fops_write(struct file *filep, const char __user *buf,
                                size_t count, loff_t *ppos)
 {
         struct vfio_container *container = filep->private_data;
-        struct vfio_iommu_driver *driver = container->iommu_driver;
+        struct vfio_iommu_driver *driver;
+        ssize_t ret = -EINVAL;
 
-        if (unlikely(!driver || !driver->ops->write))
-                return -EINVAL;
+        down_read(&container->group_lock);
+
+        driver = container->iommu_driver;
+        if (likely(driver && driver->ops->write))
+                ret = driver->ops->write(container->iommu_data,
+                                         buf, count, ppos);
+
+        up_read(&container->group_lock);
 
-        return driver->ops->write(container->iommu_data, buf, count, ppos);
+        return ret;
 }
 
 static int vfio_fops_mmap(struct file *filep, struct vm_area_struct *vma)
 {
         struct vfio_container *container = filep->private_data;
-        struct vfio_iommu_driver *driver = container->iommu_driver;
+        struct vfio_iommu_driver *driver;
+        int ret = -EINVAL;
 
-        if (unlikely(!driver || !driver->ops->mmap))
-                return -EINVAL;
+        down_read(&container->group_lock);
 
-        return driver->ops->mmap(container->iommu_data, vma);
+        driver = container->iommu_driver;
+        if (likely(driver && driver->ops->mmap))
+                ret = driver->ops->mmap(container->iommu_data, vma);
+
+        up_read(&container->group_lock);
+
+        return ret;
 }
 
 static const struct file_operations vfio_fops = {