Re: [RFC PATCH 11/21] KVM: SEV: Add TIO VMGEXIT and bind TDI

[Dan Williams <dan.j.williams@intel.com>]

Zhi Wang wrote:
> On Fri, 23 Aug 2024 23:21:25 +1000
> Alexey Kardashevskiy <aik@amd.com> wrote:
> 
> > The SEV TIO spec defines a new TIO_GUEST_MESSAGE message to
> > provide a secure communication channel between a SNP VM and
> > the PSP.
> > 
> > The defined messages provide way to read TDI info and do secure
> > MMIO/DMA setup.
> > 
> > On top of this, GHCB defines an extension to return certificates/
> > measurements/report and TDI run status to the VM.
> > 
> > The TIO_GUEST_MESSAGE handler also checks if a specific TDI bound
> > to the VM and exits the KVM to allow the userspace to bind it.
> > 
> 
> Out of curiosity, do we have to handle the TDI bind/unbind in the kernel
> space? It seems we are get the relationship between modules more
> complicated. What is the design concern that letting QEMU to handle the
> TDI bind/unbind message, because QEMU can talk to VFIO/KVM and also TSM.

Hmm, the flow I have in mind is:

Guest GHCx(BIND) => KVM => TSM GHCx handler => VFIO state update + TSM low-level BIND

vs this: (if I undertand your question correctly?)

Guest GHCx(BIND) => KVM => TSM GHCx handler => QEMU => VFIO => TSM low-level BIND

Why exit to QEMU only to turn around and call back into the kernel? VFIO
should already have the context from establishing the vPCI device as
"bind-capable" at setup time.

Maybe I misunderstood your complication concern?