Re: [PATCH 9/9] docs/system: Add documentation on support for IGVM

[Daniel P . Berrangé]

On Tue, Feb 27, 2024 at 02:50:15PM +0000, Roy Hopkins wrote:
> IGVM support has been implemented for Confidential Guests that support
> AMD SEV and AMD SEV-ES. Add some documentation that gives some
> background on the IGVM format and how to use it to configure a
> confidential guest.
> 
> Signed-off-by: Roy Hopkins <roy.hopkins@suse.com>
> ---
>  docs/system/igvm.rst  | 58 +++++++++++++++++++++++++++++++++++++++++++
>  docs/system/index.rst |  1 +
>  2 files changed, 59 insertions(+)
>  create mode 100644 docs/system/igvm.rst


> +Firmware Images with IGVM
> +-------------------------
> +
> +When an IGVM filename is specified for a Confidential Guest Support object it
> +overrides the default handling of system firmware: the firmware image, such 
> as
> +an OVMF binary should be contained as a payload of the IGVM file and not
> +provided as a flash drive. The default QEMU firmware is not automatically 
> mapped
> +into guest memory.

IIUC, in future the IGVM file could contain both the OVMF and SVSM
binaries ?

I'm also wondering if there can be dependancies between the IGVM
file and the broader QEMU configuration ?  eg if SVSM gains suupport
for data persistence, potentially we might need some pflash device
exposed as storage for SVSM to use. Would such a dependancy be
something expressed in the IGVM file, or would it be knowledge that
is out of band ?

Finally, if we think of the IGVM file as simply yet another firmware
file format, then it raises of question of integration into the
QEMU firmware descriptors.

Right now when defining a guest in libvirt if you can say 'type=bios'
or 'type=uefi', and libvirt consults the firmware descriptors to find
the binary to use.

If the OS distro provides IGVM files instead of traditional raw OVMF
binaries for SEV/TDX/etc, then from libvirt's POV I think having this
expressed in the firmware descriptors is highly desirable.


With regards,
Daniel
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