Re: [PATCH v3 0/6] igvm: Supply MADT via IGVM parameter

[Igor Mammedov <imammedo@redhat.com>]

On Fri,  9 Jan 2026 15:34:07 +0100
Oliver Steffen <osteffen@redhat.com> wrote:

> When launching using an IGVM file, supply a copy of the MADT (part of the ACPI
> tables) via an IGVM parameter (IGVM_VHY_MADT) to the guest, in addition to the
> regular fw_cfg mechanism.

I've had some questions wrt using MADT in previous version,
and possible ways to avoid issues.
not of those where addressed though.

So questions stay the same, see:
https://patchew.org/QEMU/20251211103136.1578463-1-osteffen@redhat.com/#20251219140933.7b102fc5@imammedo

> 
> The IGVM parameter can be consumed by Coconut SVSM [1], instead of relying on
> the fw_cfg interface, which has caused problems before due to unexpected access
> [2,3]. Using IGVM parameters is the default way for Coconut SVSM; switching
> over would allow removing specialized code paths for QEMU in Coconut.
> 
> In any case OVMF, which runs after SVSM has already been initialized, will
> continue reading all ACPI tables via fw_cfg and provide fixed up ACPI data to
> the OS as before.
> 
> This series makes ACPI table building more generic by making the BIOS linker
> optional. This allows the MADT to be generated outside of the ACPI build
> context. A new function (acpi_build_madt_standalone()) is added for that. With
> that, the IGVM MADT parameter field can be filled with the MADT data during
> processing of the IGVM file.
> 
> Generating the MADT twice (IGVM processing and ACPI table building) seems
> acceptable, since there is no infrastructure to obtain the MADT out of the ACPI
> table memory area during IGVM processing.
> 
> [1] https://github.com/coconut-svsm/svsm/pull/858
> [2] https://gitlab.com/qemu-project/qemu/-/issues/2882
> [3] https://github.com/coconut-svsm/svsm/issues/646
> 
> v3:
> - Pass the machine state into IGVM file processing context instead of MADT data
> - Generate MADT from inside the IGVM backend
> - Refactor: Extract common code for finding IGVM parameter from IGVM parameter handlers
> - Add NULL pointer check for igvm_get_buffer()
> 
> v2:
> - Provide more context in the message of the main commit
> - Document the madt parameter of IgvmCfgClass::process()
> - Document why no MADT data is provided the process call in sev.c
> 
> Based-on: <20251118122133.1695767-1-kraxel@redhat.com>
> Signed-off-by: Oliver Steffen <osteffen@redhat.com>
> 
> Oliver Steffen (6):
>   hw/acpi: Make BIOS linker optional
>   hw/acpi: Add standalone function to build MADT
>   igvm: Add missing NULL check
>   igvm: Add common function for finding parameter entries
>   igvm: Pass machine state to IGVM file processing
>   igvm: Fill MADT IGVM parameter field
> 
>  backends/igvm-cfg.c       |   2 +-
>  backends/igvm.c           | 169 +++++++++++++++++++++++++-------------
>  hw/acpi/aml-build.c       |   7 +-
>  hw/i386/acpi-build.c      |   8 ++
>  hw/i386/acpi-build.h      |   2 +
>  include/system/igvm-cfg.h |   3 +-
>  include/system/igvm.h     |   3 +-
>  target/i386/sev.c         |   2 +-
>  8 files changed, 132 insertions(+), 64 deletions(-)
>