Re: [PATCH v6] hw/misc/vmfwupdate: Introduce hypervisor fw-cfg interface support

["Jörg Rödel" <joro@8bytes.org>]

On Thu, Mar 13, 2025 at 08:23:44PM +0530, Ani Sinha wrote:
> Note that even with this approach where the hypervisor *thinks* it's
> dealing with a real firmware, you can imagine a small rust based
> firmware image that is loaded by the guest in the firmware region.
> This tiny firmware then jumps to a well known address (chosen by the
> guest) where IGVM is loaded and then starts executing the IGVM
> instructions.

Yes, but this way the predictable launch measurement property of IGVM
is lost, as the measurement only contains hashes for the actions
which happened before the VM was finalized and launched by the VMM. The
SEV policy can also not be changed anymore when the guest is running.

Anyway, I think it doesn't matter much whether the IGVM is parsed in
guest context or by QEMU, as long as the resulting measurement is the
same as if the file was loaded at initial VM launch.

Given that QEMU will hopefully get IGVM backend support soon, there is
some value and saved effort in just passing the IGVM data to the VMM via
the vmfwupdate interface and let QEMU do the rest.

Regards,

	Joerg