On Wed, Oct 16, 2024 at 09:56:51AM +0800, Zhangfei Gao wrote:
> On Wed, 16 Oct 2024 at 02:44, Nicolin Chen <nicolinc@xxxxxxxxxx> wrote:
> >
> > On Mon, Oct 14, 2024 at 07:01:40PM -0700, Nicolin Chen wrote:
> > > On Tue, Oct 15, 2024 at 09:15:01AM +0800, Zhangfei Gao wrote:
> > >
> > > > > > iommufd_device_bind
> > > > > > iommufd_device_attach
> > > > > > iommufd_vdevice_alloc_ioctl
> > > > > >
> > > > > > iommufd_device_detach
> > > > > > iommufd_device_unbind // refcount check fail
> > > > > > iommufd_vdevice_destroy ref--
> > > > >
> > > > > Things should be symmetric. As you suspected, vdevice should be
> > > > > destroyed before iommufd_device_detach.
> > > >
> > > > I am trying based on your for_iommufd_viommu_p2-v3 branch, do you have
> > > > this issue?
> > > > In checking whether close fd before unbind?
> > >
> > > Oops, my bad. I will provide a fix.
> >
> > This should fix the problem:
> >
> > ---------------------------------------------------------------------
> > diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> > index 5fd3dd420290..13100cfea29d 100644
> > --- a/drivers/iommu/iommufd/device.c
> > +++ b/drivers/iommu/iommufd/device.c
> > @@ -277,6 +277,11 @@ EXPORT_SYMBOL_NS_GPL(iommufd_ctx_has_group, IOMMUFD);
> > */
> > void iommufd_device_unbind(struct iommufd_device *idev)
> > {
> > + mutex_lock(&idev->igroup->lock);
> > + /* idev->vdev object should be destroyed prior, yet just in case.. */
> > + if (idev->vdev)
> > + iommufd_object_remove(idev->ictx, NULL, idev->vdev->obj.id, 0);
> > + mutex_unlock(&idev->igroup->lock);
> > iommufd_object_destroy_user(idev->ictx, &idev->obj);
> > }
> > EXPORT_SYMBOL_NS_GPL(iommufd_device_unbind, IOMMUFD);
> > ---------------------------------------------------------------------
>
> Not yet
> [ 574.162112] Unable to handle kernel NULL pointer dereference at
> virtual address 0000000000000004
> [ 574.261102] pc : iommufd_object_remove+0x7c/0x278
> [ 574.265795] lr : iommufd_device_unbind+0x44/0x98
> in check
Hmm, it's kinda odd it crashes inside iommufd_object_remove().
Did you happen to change something there?
The added iommufd_object_remove() is equivalent to userspace
calling the destroy ioctl on the vDEVICE object.
Nicolin
