Hi Yi,
On 1/17/23 14:49, Yi Liu wrote:
> Allow the vfio_device file to be in a state where the device FD is
> opened but the device cannot be used by userspace (i.e. its .open_device()
> hasn't been called). This inbetween state is not used when the device
> FD is spawned from the group FD, however when we create the device FD
> directly by opening a cdev it will be opened in the blocked state.
Please explain why this is needed in the commit message (although you
evoked the rationale in the cover letter).
Eric
>
> In the blocked state, currently only the bind operation is allowed,
> other device accesses are not allowed. Completing bind will allow user
> to further access the device.
>
> This is implemented by adding a flag in struct vfio_device_file to mark
> the blocked state and using a simple smp_load_acquire() to obtain the
> flag value and serialize all the device setup with the thread accessing
> this device.
>
> Due to this scheme it is not possible to unbind the FD, once it is bound,
> it remains bound until the FD is closed.
>
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> ---
> drivers/vfio/vfio.h | 1 +
> drivers/vfio/vfio_main.c | 29 +++++++++++++++++++++++++++++
> 2 files changed, 30 insertions(+)
>
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index 3d8ba165146c..c69a9902ea84 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -20,6 +20,7 @@ struct vfio_device_file {
> struct vfio_device *device;
> struct kvm *kvm;
> struct iommufd_ctx *iommufd;
> + bool access_granted;
> };
>
> void vfio_device_put_registration(struct vfio_device *device);
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 3df71bd9cd1e..d442ebaa4b21 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -430,6 +430,11 @@ int vfio_device_open(struct vfio_device_file *df)
> }
> }
>
> + /*
> + * Paired with smp_load_acquire() in vfio_device_fops::ioctl/
> + * read/write/mmap
> + */
> + smp_store_release(&df->access_granted, true);
> return 0;
> }
>
> @@ -1058,8 +1063,14 @@ static long vfio_device_fops_unl_ioctl(struct file *filep,
> {
> struct vfio_device_file *df = filep->private_data;
> struct vfio_device *device = df->device;
> + bool access;
> int ret;
>
> + /* Paired with smp_store_release() in vfio_device_open() */
> + access = smp_load_acquire(&df->access_granted);
> + if (!access)
> + return -EINVAL;
> +
> ret = vfio_device_pm_runtime_get(device);
> if (ret)
> return ret;
> @@ -1086,6 +1097,12 @@ static ssize_t vfio_device_fops_read(struct file *filep, char __user *buf,
> {
> struct vfio_device_file *df = filep->private_data;
> struct vfio_device *device = df->device;
> + bool access;
> +
> + /* Paired with smp_store_release() in vfio_device_open() */
> + access = smp_load_acquire(&df->access_granted);
> + if (!access)
> + return -EINVAL;
>
> if (unlikely(!device->ops->read))
> return -EINVAL;
> @@ -1099,6 +1116,12 @@ static ssize_t vfio_device_fops_write(struct file *filep,
> {
> struct vfio_device_file *df = filep->private_data;
> struct vfio_device *device = df->device;
> + bool access;
> +
> + /* Paired with smp_store_release() in vfio_device_open() */
> + access = smp_load_acquire(&df->access_granted);
> + if (!access)
> + return -EINVAL;
>
> if (unlikely(!device->ops->write))
> return -EINVAL;
> @@ -1110,6 +1133,12 @@ static int vfio_device_fops_mmap(struct file *filep, struct vm_area_struct *vma)
> {
> struct vfio_device_file *df = filep->private_data;
> struct vfio_device *device = df->device;
> + bool access;
> +
> + /* Paired with smp_store_release() in vfio_device_open() */
> + access = smp_load_acquire(&df->access_granted);
> + if (!access)
> + return -EINVAL;
>
> if (unlikely(!device->ops->mmap))
> return -EINVAL;
