[RFC PATCH 00/12] Private MMIO support for private assigned dev

[Xu Yilun]

On Thu, May 15, 2025 at 04:21:27PM -0300, Jason Gunthorpe wrote:
> On Fri, May 16, 2025 at 02:02:29AM +0800, Xu Yilun wrote:
> > > IMHO, I think it might be helpful that you can picture out what are the
> > > minimum requirements (function/life cycle) to the current IOMMUFD TSM
> > > bind architecture:
> > > 
> > > 1.host tsm_bind (preparation) is in IOMMUFD, triggered by QEMU handling
> > > the TVM-HOST call.
> > > 2. TDI acceptance is handled in guest_request() to accept the TDI after
> > > the validation in the TVM)
> > 
> > I'll try my best to brainstorm and make a flow in ASCII. 
> > 
> > (*) means new feature
> > 
> > 
> >       Guest          Guest TSM       QEMU           VFIO            IOMMUFD       host TSM          KVM 
> >       -----          ---------       ----           ----            -------       --------          ---
> > 1.                                                                               *Connect(IDE)
> > 2.                                 Init vdev            
> 
> open /dev/vfio/XX as a VFIO action
> 
> Then VFIO attaches to IOMMUFD as an iommufd action creating the idev
> 
> > 3.                                *create dmabuf   
> > 4.                                               *export dmabuf                              
> > 5.                                create memslot
> > 6.                                                                                              *import dmabuf
> > 7.                                setup shared DMA
> > 8.                                                                 create hwpt
> > 9.                                               attach hwpt
> > 10.                                  kvm run
> > 11.enum shared dev
> > 12.*Connect(Bind)
> > 13.                  *GHCI Bind
> > 14.                                  *Bind
> > 15                                                                 CC viommu alloc
> > 16.                                                                vdevice allloc
> 
> viommu and vdevice creation happen before KVM run. The vPCI function
> is visible to the guest from the very start, even though it is in T=0
> mode. If a platform does not require any special CC steps prior to KVM
> run then it just has a NOP for these functions.
> 

Fine.

> What you have here is some new BIND operation against the already
> existing vdevice as we discussed earlier.
> 
> > 16.                                              *attach vdev
> > 17.                                                               *setup CC viommu
> > 18                                                                 *tsm_bind
> > 19.                                                                                  *bind
> > 20.*Attest
> > 21.               *GHCI get CC info
> > 22.                                 *get CC info
> > 23.                                                                *vdev guest req
> > 24.                                                                                 *guest req
> > 25.*Accept
> > 26.             *GHCI accept MMIO/DMA
> > 27.                                *accept MMIO/DMA
> > 28.                                                               *vdev guest req
> > 29.                                                                                 *guest req
> > 30.                                                                                              *map private MMIO
> > 31.             *GHCI start tdi
> > 32.                                *start tdi
> > 33.                                                               *vdev guest req
> > 34.                                                                                 *guest req
> 
> This seems reasonable you want to have some generic RPC scheme to
> carry messages fro mthe VM to the TSM tunneled through the iommufd
> vdevice (because the vdevice has the vPCI ID, the KVM ID, the VIOMMU
> id and so on)
> 
> > 35.Workload...
> > 36.*disconnect(Unbind)
> > 37.              *GHCI unbind
> > 38.                                *Unbind
> > 39.                                            *detach vdev
> 
> unbind vdev. vdev remains until kvm is stopped.
> 
> > 40.                                                               *tsm_unbind
> > 41.                                                                                 *TDX stop tdi
> > 42.                                                                                 *TDX disable mmio cb
> > 43.                                            *cb dmabuf revoke
> > 44.                                                                                               *unmap private MMIO
> > 45.                                                                                 *TDX disable dma cb
> > 46.                                                              *cb disable CC viommu
> 
> I don't know why you'd disable a viommu while the VM is running,
> doesn't make sense.

Here it means remove the CC setup for viommu, shared setup is still
kept.

It is still because of the TDX enforcement on Unbind :(

  1. STOP TDI via TDISP message STOP_INTERFACE
  2. Private MMIO unmap from Secure EPT
  3. Trusted Device Context Table cleanup for the TDI
  4. TDI ownership reclaim and metadata free

It is doing Step 3 so that the TDI could finally been removed.

Please also note I does CC viommu setup on "Bind".

Thanks,
Yilun

> 
> > 47.                                                                                 *TDX tdi free
> > 48.                                                                                 *enable mmio
> > 49.                                            *cb dmabuf recover
> > 50.workable shared dev
> 
> This is a nice chart, it would be good to see a comparable chart for
> AMD and ARM
> 
> Jason