On Fri, Nov 21, 2025 at 08:13:38AM +0100, Tian, Kevin wrote:
> > From: Winiarski, Michal <[email protected]>
> > Sent: Thursday, November 20, 2025 8:37 PM
> >
> > Resetting the migration device state is typically delegated to PCI
> > .reset_done() callback.
> > With VFIO, reset is usually called under vdev->memory_lock, which causes
> > lockdep to report a following circular locking dependency scenario:
> >
> > 0: set_device_state
> > driver->state_mutex -> migf->lock
> > 1: data_read
> > migf->lock -> mm->mmap_lock
> > 2: vfio_pin_dma
> > mm->mmap_lock -> vdev->memory_lock
> > 3: vfio_pci_ioctl_reset
> > vdev->memory_lock -> driver->state_mutex
> >
> > Introduce a .migration_reset_state() callback called outside of
> > vdev->memory_lock to break the dependency chain.
>
> so it kind of unifies the deferred_reset logic cross all drivers.
>
> sounds reasonable as nobody should expect a concrete sequence of
> a reset done vs. a racing set_device_state.
>
> >
> > +static void vfio_pci_dev_migration_reset_state(struct vfio_pci_core_device
> > *vdev)
> > +{
> > + lockdep_assert_not_held(&vdev->memory_lock);
> > +
> > + if (!vdev->vdev.mig_ops->migration_reset_state)
> > + return;
>
> mig_ops could be NULL.
I'll replace it with pure mig_ops check, as the migration_reset_state()
is not optional.
>
> > @@ -1230,6 +1242,8 @@ static int vfio_pci_ioctl_reset(struct
> > vfio_pci_core_device *vdev,
> > ret = pci_try_reset_function(vdev->pdev);
> > up_write(&vdev->memory_lock);
> >
> > + vfio_pci_dev_migration_reset_state(vdev);
> > +
>
> only if the previous reset succeeds.
Ok.
>
> > @@ -2486,8 +2501,10 @@ static int vfio_pci_dev_set_hot_reset(struct
> > vfio_device_set *dev_set,
> >
> > err_undo:
> > list_for_each_entry_from_reverse(vdev, &dev_set->device_list,
> > - vdev.dev_set_list)
> > + vdev.dev_set_list) {
> > up_write(&vdev->memory_lock);
> > + vfio_pci_dev_migration_reset_state(vdev);
> > + }
>
> ditto
>
> btw some reset paths are missed in drivers/vfio/pci/vfio_pci_config.c,
> e.g. for vFLR emulation.
>
I'll add the missing paths in v2.
Thanks,
-Michał
