[edk2-devel] [PATCH 18/23] OvmfPkg: Enable Tdx in SecMain.c

[Min Xu]

On August 19, 2021 2:50 PM, Gerd Hoffmann wrote:
> > +/**
> > +  In Tdx guest, some information need to be passed from host VMM to
> guest
> > +  firmware. For example, the memory resource, etc. These information are
> > +  prepared by host VMM and put in HobList which is described in
> TdxMetadata.
> 
> What kind of information is passed to the guest here?
Please see https://software.intel.com/content/dam/develop/external/us/en/documents/tdx-virtual-firmware-design-guide-rev-1.pdf
Section 4.2 TD Hand-Off Block (HOB)
> 
> qemu has fw_cfg to pass information from the VMM to the guest firmware.
> What are the reasons to not use fw_cfg?
Not all the VMM support fw_cfg. Cloud-Hypervisor is the example. 
https://github.com/cloud-hypervisor/cloud-hypervisor
TD Hob list gives Cloud-Hypervisor a chance to pass information to guest firmware. 
For example, ACPI can be downloaded from QEMU via fw_cfg to firmware. But
Cloud-Hypervisor cannot pass ACPI via fw_cfg. In this situation, TD Hob can resolve
this problem.
> 
> thanks,
>   Gerd



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