Re: [RFC PATCH 08/12] vfio/pci: Create host unaccessible dma-buf for private device

[Baolu Lu]

On 1/15/25 21:01, Jason Gunthorpe wrote:
> On Wed, Jan 15, 2025 at 11:57:05PM +1100, Alexey Kardashevskiy wrote:
> > On 15/1/25 00:35, Jason Gunthorpe wrote:
> > > On Tue, Jun 18, 2024 at 07:28:43AM +0800, Xu Yilun wrote:
> > >
> > > > > is needed so the secure world can prepare anything it needs prior to
> > > > > starting the VM.
> > > > OK. From Dan's patchset there are some touch point for vendor tsm
> > > > drivers to do secure world preparation. e.g. pci_tsm_ops::probe().
> > > >
> > > > Maybe we could move to Dan's thread for discussion.
> > > >
> > > > https://lore.kernel.org/linux- 
> > > > coco/173343739517.1074769.13134786548545925484.stgit@dwillia2- 
> > > > xfh.jf.intel.com/
> > > I think Dan's series is different, any uapi from that series should
> > > not be used in the VMM case. We need proper vfio APIs for the VMM to
> > > use. I would expect VFIO to be calling some of that infrastructure.
> > Something like this experiment?
> >
> > https://github.com/aik/linux/commit/ 
> > ce052512fb8784e19745d4cb222e23cabc57792e
> Yeah, maybe, though I don't know which of vfio/iommufd/kvm should be
> hosting those APIs, the above does seem to be a reasonable direction.
>
> When the various fds are closed I would expect the kernel to unbind
> and restore the device back.

I am curious about the value of tsm binding against an iomnufd_vdevice
instead of the physical iommufd_device.

It is likely that the kvm pointer should be passed to iommufd during the
creation of a viommu object. If my recollection is correct, the arm
smmu-v3 needs it to obtain the vmid to setup the userspace event queue:

struct iommufd_viommu *arm_vsmmu_alloc(struct device *dev,
                                       struct iommu_domain *parent,
                                       struct iommufd_ctx *ictx,
                                       unsigned int viommu_type)
{

[...]

        /* FIXME Move VMID allocation from the S2 domain allocation to 
here */
        vsmmu->vmid = s2_parent->s2_cfg.vmid;

        return &vsmmu->core;
}

Intel TDX connect implementation also needs a reference to the kvm
pointer to obtain the secure EPT information. This is crucial because
the CPU's page table must be shared with the iommu. I am not sure
whether the amd architecture has a similar requirement.

---
baolu