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(-)
>