This series enables Kexec Handover (KHO) on LoongArch, making it the
third architecture (after x86 and arm64) to set
ARCH_SUPPORTS_KEXEC_HANDOVER. That is the only remaining gate for Live
Update (LUO) to run on LoongArch.
The hard part is the transport: how the first kernel hands the KHO state
(the KHO FDT and the scratch region) to the second kernel across kexec.
Why not the command line or an FDT
----------------------------------
LoongArch boots from EFI, but unlike arm64 and riscv its efistub does not
build a boot FDT. It passes the EFI system table and the command line
straight to the core kernel [1]. There is no /chosen node to carry the
blob, so the arm64 path (drivers/of/kexec.c:kho_add_chosen() writes
linux,kho-fdt and linux,kho-scratch; drivers/of/fdt.c:
early_init_dt_check_kho() reads them) does not apply.
Two earlier transports were tried and rejected:
* v1 put the handover addresses on the kernel command line. Pratyush
found that odd and asked for a DT-based alternative.
* v2/v3 synthesized an FDT and rewrote the DEVICE_TREE_GUID entry in the
EFI config table so the generic FDT reader would find it. Pratyush
called that "even more hacky" than the command line [2].
The v4 transport
----------------
v4 follows the x86 setup_data idea, in EFI terms. The first kernel packs
the KHO state into a small struct (linux_efi_kho_data: fdt addr/size and
scratch addr/size), appends a pointer to it under a dedicated
LINUX_EFI_KHO_TABLE_GUID entry in a new EFI config table, loads both as
kexec segments, and switches st->tables before jumping. The second kernel
scans the config table for that GUID in setup_arch() and calls
kho_populate() directly. This is the approach proposed in [3].
It addresses both objections: nothing is exposed on the command line, and
no FDT is synthesized. It also meets Huacai's constraint: it reuses the
EFI system table LoongArch already has, with no dependency on a boot FDT
the efistub never creates.
Patch layout
------------
Patches 1-2 implement the transport. Patch 1 adds the EFI config table
GUID and the handover struct to include/linux/efi.h. It is split out so
the EFI maintainers can review it on its own. Patch 2 wires up the
LoongArch side: ARCH_SUPPORTS_KEXEC_HANDOVER, the write side in
machine_kexec_file.c, the st->tables switch in machine_kexec(), and the
reader in setup_arch().
Patch 3 is a build fix for kernel/liveupdate/luo_session.c that the
series depends on under CONFIG_KFENCE=y on LoongArch. It was sent
standalone as v2 and acked by Mike. It is folded in here at his request
to send it along with this series [4].
Patch 4 adds LoongArch vmtest support to the KHO selftests and folds in
the two points Mike raised on v3 (use "VM" instead of the ad-hoc
"virt machine"; run every architecture under timeout(1), not only
LoongArch).
Patch 1 is aimed at the EFI tree. Patches 2-4 are aimed at the LoongArch
and KHO trees. I expect the whole series to go through the KHO tree with
Ard's and Huacai's acks.
Changes since v3
----------------
* Rework the transport: drop the synthesized FDT and the
DEVICE_TREE_GUID rewrite. Pass the KHO state through a dedicated EFI
configuration table GUID and call kho_populate() directly (patches
1, 2).
* Fold in the luo_session build fix (previously standalone v2, acked by
Mike) as patch 3, at his request.
* selftests: address Mike's v3 review (use "VM"; always run under
timeout(1)).
* Rebase onto v7.2-rc6.
[1] Huacai Chen:
https://lore.kernel.org/r/caahv-h5b6mj2-affkstj4f8eemvvpogxody2qnudkd2ksz2...@mail.gmail.com/
[2] Pratyush Yadav: https://lore.kernel.org/r/[email protected]/
[3] https://lore.kernel.org/r/[email protected]/
[4] Mike Rapoport: https://lore.kernel.org/r/[email protected]/
George Guo (4):
efi: add a KHO configuration table GUID
LoongArch: kexec: add KHO support
liveupdate: luo_session: include linux/mm.h for virt/phys translation
selftests/kho: add LoongArch vmtest support
arch/loongarch/Kconfig | 3 +
arch/loongarch/include/asm/kexec.h | 7 ++
arch/loongarch/kernel/machine_kexec.c | 16 +++
arch/loongarch/kernel/machine_kexec_file.c | 131 +++++++++++++++++++++
arch/loongarch/kernel/setup.c | 41 +++++++
include/linux/efi.h | 24 ++++
kernel/liveupdate/luo_session.c | 1 +
tools/testing/selftests/kho/loongarch.conf | 11 ++
tools/testing/selftests/kho/vmtest.sh | 22 ++--
9 files changed, 249 insertions(+), 7 deletions(-)
create mode 100644 tools/testing/selftests/kho/loongarch.conf
--
2.53.0
