On Fri, 2 Jun 2023 05:16:36 -0700 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]> > Reviewed-by: Kevin Tian <[email protected]> > Reviewed-by: Jason Gunthorpe <[email protected]> > Reviewed-by: Eric Auger <[email protected]> > Tested-by: Terrence Xu <[email protected]> > Tested-by: Nicolin Chen <[email protected]> > Tested-by: Matthew Rosato <[email protected]> > Tested-by: Yanting Jiang <[email protected]> > Tested-by: Shameer Kolothum <[email protected]> > Signed-off-by: Yi Liu <[email protected]> > --- > drivers/vfio/group.c | 11 ++++++++++- > drivers/vfio/vfio.h | 1 + > drivers/vfio/vfio_main.c | 16 ++++++++++++++++ > 3 files changed, 27 insertions(+), 1 deletion(-) > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > index caf53716ddb2..088dd34c8931 100644 > --- a/drivers/vfio/group.c > +++ b/drivers/vfio/group.c > @@ -194,9 +194,18 @@ static int vfio_df_group_open(struct vfio_device_file > *df) > df->iommufd = device->group->iommufd; > > ret = vfio_df_open(df); > - if (ret) > + if (ret) { > df->iommufd = NULL; > + goto out_put_kvm; > + } > + > + /* > + * Paired with smp_load_acquire() in vfio_device_fops::ioctl/ > + * read/write/mmap and vfio_file_has_device_access() > + */ > + smp_store_release(&df->access_granted, true); > > +out_put_kvm: > if (device->open_count == 0) > vfio_device_put_kvm(device); > > diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h > index f9eb52eb9ed7..fdf2fc73f880 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; Should we make this a more strongly defined data type and later move devid (u32) here to partially fill the hole created? I think this is being placed towards the front of the data structure for cache line locality given this is a hot path for file operations. But bool types have an implementation dependent size, making them difficult to pack. Also there will be a tendency to want to make this a bit field, which is probably not compatible with the smp lockless operations being used here. We might get in front of these issues if we just define it as a u8 now. Thanks, Alex > 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 a3c5817fc545..4c8b7713dc3d 100644 > --- a/drivers/vfio/vfio_main.c > +++ b/drivers/vfio/vfio_main.c > @@ -1129,6 +1129,10 @@ static long vfio_device_fops_unl_ioctl(struct file > *filep, > struct vfio_device *device = df->device; > int ret; > > + /* Paired with smp_store_release() following vfio_df_open() */ > + if (!smp_load_acquire(&df->access_granted)) > + return -EINVAL; > + > ret = vfio_device_pm_runtime_get(device); > if (ret) > return ret; > @@ -1156,6 +1160,10 @@ 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; > > + /* Paired with smp_store_release() following vfio_df_open() */ > + if (!smp_load_acquire(&df->access_granted)) > + return -EINVAL; > + > if (unlikely(!device->ops->read)) > return -EINVAL; > > @@ -1169,6 +1177,10 @@ static ssize_t vfio_device_fops_write(struct file > *filep, > struct vfio_device_file *df = filep->private_data; > struct vfio_device *device = df->device; > > + /* Paired with smp_store_release() following vfio_df_open() */ > + if (!smp_load_acquire(&df->access_granted)) > + return -EINVAL; > + > if (unlikely(!device->ops->write)) > return -EINVAL; > > @@ -1180,6 +1192,10 @@ 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; > > + /* Paired with smp_store_release() following vfio_df_open() */ > + if (!smp_load_acquire(&df->access_granted)) > + return -EINVAL; > + > if (unlikely(!device->ops->mmap)) > return -EINVAL; >
