Re: [PATCH v2 5/9] hw/misc/vmlaunchupdate: Introduce hypervisor fw-cfg interface support

On Tue, Jul 14, 2026 at 08:15:24AM +0530, Ani Sinha wrote:
> VM launch update is a mechanism where the virtual machines can use IGVM
> file bundle to boot into a trusted execution environment without
> having to depend on a untrusted party to provide the IGVM bundle or firmware
> image. This is particularly useful for confidential virtual machines that
> are deployed in the cloud where the tenant and the cloud provider are two
> different entities. In this scenario, virtual machines can bring their own
> trusted IGVM file containing a trusted firmware image
> bundled as a part of their filesystem and then use this hypervisor interface
> to update to a trusted and deterministic boot state.
> This also allows the guests to have a consistent measurements on the firmware
> image.
> 
> Currently, this mechanism only works if the VM was started with IGVM in the
> first place.
> 
> This change introduces support for the fw-cfg based hypervisor interface
> and the corresponding device. The interface is made generic
> enough so that guests are free to use their own ABI to pass required
> information between initial and trusted execution contexts (where they are
> running their own trusted boot state) without the hypervisor getting
> involved in between.
> 
> Currently, this device is only supported for x86 machines. Presence of
> IGVM host libraries is also required for parsing IGVM files. Hence, the device
> cannot be initialized for other machine types or hosts where IGVM support
> is not present. Trying to initialize it for arm for example will lead to failure:
> 
> $ ./qemu-system-arm -device vm-launch-update -machine virt
> qemu-system-arm: -device vmfwupdate: This machine does not support vm-launch-update device
> 
> Functional and qtests will be added in a subsequent patch.
> 
> CC: Alex Graf <[email protected]>
> CC: Gerd Hoffman <[email protected]>

Reviewed-by: Gerd Hoffmann <[email protected]>