Re: [RFC PATCH 3/3] iommufd/tsm: Add tsm_bind/unbind iommufd ioctls

[Xu Yilun <yilun.xu@linux.intel.com>]

On Tue, Jun 03, 2025 at 09:14:56AM -0300, Jason Gunthorpe wrote:
> On Tue, Jun 03, 2025 at 06:50:13PM +0800, Xu Yilun wrote:
> 
> > I see. But I'm not sure if it can be a better story than ioctl(VFIO_TSM_BIND).
> > You want VFIO unaware of TSM bind, e.g. try to hide pci_request/release_region(),
> > but make VFIO aware of TSM unbind, which seems odd ...
> 
> request_region does not need to be done dynamically. It should be done
> once when the VFIO cdev is opened. If you need some new ioctl to put
> VFIO in a CC compatible mode then it should do all this stuff once. It
> doesn't need to be dynamic.

But the unbind needs to be dynamic.

> 
> I think all you want is to trigger VFIO to invalidate its MMIOs when
> bind/unbind happens.

Trigger VFIO to passively invalidate MMIOs during unbind is a TDX
specific requirement.


Another more general requirement is, VFIO needs to trigger unbind when
VFIO wants to actively invalidate MMIOs. e.g. before VFIO resets device.
That is the dynamic unbind thing.

The reason is the secure DMA silent drop issue.  Intel, and seems
AMD (Alexey please confirm) both implemented some policy in FW/HW to block
this issue. But the consequences are fatal to OS, so better we avoid
this.

[1]: https://lore.kernel.org/all/aDnXxk46kwrOcl0i@yilunxu-OptiPlex-7050/

Thanks,
Yilun

> 
> Jason