Hi, George,
On Fri, Aug 7, 2026 at 6:38 PM George Guo <[email protected]> wrote:
>
> From: George Guo <[email protected]>
>
> Kexec Handover (KHO) passes the address of its state FDT and of its
> scratch area from the current kernel to the next one. On architectures
> that boot with a device tree, the current kernel writes the
> linux,kho-fdt and linux,kho-scratch properties into /chosen, and the next
> kernel reads them back in early_init_dt_check_kho().
>
> Architectures that boot through EFI without a device tree have no such
> channel. LoongArch is one of them: its efistub passes the EFI system
> table and the command line to the core kernel directly and never creates
> an FDT. x86 has the same problem and carries the state out of band
> instead, in a struct kho_data in the setup_data chain of its boot
> protocol.
>
> Add an out-of-band channel for EFI: a LINUX_EFI_KHO_TABLE_GUID
> configuration table entry, under a randomly generated GUID, pointing at a
> struct linux_efi_kho_data. The
> current kernel loads the structure and an extended configuration table as
> kexec segments, then switches the EFI system table to the new table
> before jumping. The next kernel finds the entry by GUID and calls
> kho_populate().
>
> The structure carries no version field. An incompatible change to the
> layout must use a new GUID, which is the usual rule for EFI configuration
> tables. The handover payload itself is versioned separately, by the
> compatible string of the KHO state FDT that kho_populate() checks.
>
> This patch adds the definitions only. LoongArch is the first user; any
> other EFI architecture without a boot FDT can use the same channel.
>
> Signed-off-by: George Guo <[email protected]>
> ---
> include/linux/efi.h | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index ccbc35479684..789ab9e4312a 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -422,6 +422,7 @@ void efi_native_runtime_setup(void);
> #define LINUX_EFI_COCO_SECRET_AREA_GUID EFI_GUID(0xadf956ad,
> 0xe98c, 0x484c, 0xae, 0x11, 0xb5, 0x1c, 0x7d, 0x33, 0x64, 0x47)
> #define LINUX_EFI_BOOT_MEMMAP_GUID EFI_GUID(0x800f683f, 0xd08b,
> 0x423a, 0xa2, 0x93, 0x96, 0x5c, 0x3c, 0x6f, 0xe2, 0xb4)
> #define LINUX_EFI_UNACCEPTED_MEM_TABLE_GUID EFI_GUID(0xd5d1de3c, 0x105c,
> 0x44f9, 0x9e, 0xa9, 0xbc, 0xef, 0x98, 0x12, 0x00, 0x31)
> +#define LINUX_EFI_KHO_TABLE_GUID EFI_GUID(0xc941b6c7, 0x7b3f,
> 0x4af6, 0x9e, 0x50, 0xfc, 0xb3, 0xa8, 0x86, 0x8a, 0x17)
I don't know whether it is allowed to define a new TABLE ID while
doesn't touch the UEFI SPEC.
Huacai
>
> #define RISCV_EFI_BOOT_PROTOCOL_GUID EFI_GUID(0xccd15fec, 0x6f73,
> 0x4eec, 0x83, 0x95, 0x3e, 0x69, 0xe4, 0xb9, 0x40, 0xbf)
>
> @@ -1271,6 +1272,29 @@ struct linux_efi_memreserve {
>
> void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size);
>
> +/*
> + * The LINUX_EFI_KHO_TABLE_GUID config table points to this structure. It
> + * carries the kexec handover (KHO) state from the current kernel to the next
> + * one: the addresses of the KHO state FDT and of the scratch area.
> + *
> + * This is the handover channel for architectures that boot through EFI
> without
> + * a device tree, where the /chosen linux,kho-fdt and linux,kho-scratch
> + * properties read by early_init_dt_check_kho() are not available. The
> current
> + * kernel loads the structure and an extended configuration table as kexec
> + * segments; the next kernel finds it by GUID and calls kho_populate().
> + *
> + * The layout is an ABI between the two kernels and is fixed. It carries no
> + * version field: an incompatible change must use a new GUID, and the
> handover
> + * payload itself is versioned separately by the compatible string of the KHO
> + * state FDT, which kho_populate() checks.
> + */
> +struct linux_efi_kho_data {
> + u64 fdt_addr;
> + u64 fdt_size;
> + u64 scratch_addr;
> + u64 scratch_size;
> +} __packed;
> +
> /*
> * The LINUX_EFI_MOK_VARIABLE_TABLE_GUID config table can be provided
> * to the kernel by an EFI boot loader. The table contains a packed
> --
> 2.53.0
>
