Re: [PATCH RFCv1 07/14] iommufd: Add viommu set/unset_dev_id ops

Nicolin Chen
2024-05-13T04:39:34Z

On Sun, May 12, 2024 at 11:46:54AM -0300, Jason Gunthorpe wrote:
> On Fri, Apr 12, 2024 at 08:47:04PM -0700, Nicolin Chen wrote:
> > Add a pair of ops to set and unet device's virtual ID that belongs to
> > a viommu object. They will be used, in the following patch, by iommufd
> > to support some HW-acceleration feature from the host level.
> >
> > For instance, every device behind an ARM SMMU has a Stream ID. The ID
> > is used by ATC invalidation commands so SMMU HW can direct invalidation
> > requests to the corresponding PCI device where the ID belongs to. In a
> > virtualization use case, a passthroughed device in the VM will have a
> > virtuail Stream ID, used by the ATC invalidation commands in the guest
> > system. NVIDIA's CMDQV extension for SMMUv3 provides a v-interface to
> > execute the guest-level ATC invalidation commands directly, yet needs
> > the HW to be aware of its virtual Stream ID so it can replace with its
> > physical Stream ID.
>
> I imagine using this as well for the ATC invalidation commands. It
> would be very easy and simplifying if the command fixup just extracted
> the vSID from the ATC invalidation and used an xarray to turn it into
> a pSID and then pushed the resulting command.

You mean the nested SMMU series right? Actually the set_dev_id
ioctl was a part of that until we wanted to try DEV_INVALIDATE.

So again, yes, it makes sense to me that we move viommu and the
set_dev_id to the nested series, and then drop DEV_INVALIDATE.

Thanks
Nicolin