On Mon, 13 Feb 2023 07:13:40 -0800 Yi Liu <[email protected]> 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. > > The reason for the inbetween state is that userspace only gets a FD but > doesn't gain access permission until binding the FD to an iommufd. So in > the blocked state, only the bind operation is 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. > > Following this lockless scheme, it can safely handle the device FD > unbound->bound but it cannot handle bound->unbound. To allow this we'd > need to add a lock on all the vfio ioctls which seems costly. So once > device FD is bound, it remains bound until the FD is closed. > > Suggested-by: Jason Gunthorpe <[email protected]> > Signed-off-by: Yi Liu <[email protected]> > Reviewed-by: Kevin Tian <[email protected]> > --- > drivers/vfio/vfio.h | 1 + > drivers/vfio/vfio_main.c | 34 +++++++++++++++++++++++++++++++++- > 2 files changed, 34 insertions(+), 1 deletion(-) > > diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h > index 11e56fe079a1..d56cdb114024 100644 > --- a/drivers/vfio/vfio.h > +++ b/drivers/vfio/vfio.h > @@ -18,6 +18,7 @@ struct vfio_container; > > struct vfio_device_file { > struct vfio_device *device; > + bool access_granted; > spinlock_t kvm_ref_lock; /* protect kvm field */ > struct kvm *kvm; > struct iommufd_ctx *iommufd; /* protected by struct > vfio_device_set::lock */ > diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c > index c517252aba19..2267057240bd 100644 > --- a/drivers/vfio/vfio_main.c > +++ b/drivers/vfio/vfio_main.c > @@ -476,7 +476,15 @@ int vfio_device_open(struct vfio_device_file *df) > device->open_count--; > } > > - return ret; > + if (ret) > + return ret; > + > + /* > + * Paired with smp_load_acquire() in vfio_device_fops::ioctl/ > + * read/write/mmap > + */ > + smp_store_release(&df->access_granted, true); > + return 0; > } > > void vfio_device_close(struct vfio_device_file *df) > @@ -1104,8 +1112,14 @@ 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; > + Nit, if (!smp_load_acquire(&df->access_granted)) ... Thanks, Alex > ret = vfio_device_pm_runtime_get(device); > if (ret) > return ret; > @@ -1132,6 +1146,12 @@ 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; > @@ -1145,6 +1165,12 @@ 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; > @@ -1156,6 +1182,12 @@ 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;
