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.
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. Coconut SVSM needs to know the SMP configuration, but does not look at any other ACPI data, nor does it interact with the PCI bus settings. Since the MADT is static and not linked with other ACPI tables, it can be supplied stand-alone like this. 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. 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. [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 v4: - Add ACPI table checksum calculation without BIOS linker, used for the standalone MADT. - Don't pass ConfidentialGuestState into the IGVM backend anymore. Not needed, since we already have the full MachineState there now. - Move the NULL check patch out into a new series (to be posted). - Address remaining cleanup comments. 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: <[email protected]> Signed-off-by: Oliver Steffen <[email protected]> Oliver Steffen (5): hw/acpi: Make BIOS linker optional hw/acpi: Add standalone function to build MADT 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 | 179 +++++++++++++++++++++++--------------- hw/acpi/aml-build.c | 29 +++++- hw/i386/acpi-build.c | 9 ++ hw/i386/acpi-build.h | 2 + include/system/igvm-cfg.h | 3 +- include/system/igvm.h | 5 +- target/i386/sev.c | 3 +- 8 files changed, 155 insertions(+), 77 deletions(-) -- 2.52.0
