Re: [PATCH v4 2/4] LoongArch: kexec: add KHO support

Hi, George,

On Fri, Aug 7, 2026 at 6:38 PM George Guo <[email protected]> wrote:
>
> From: George Guo <[email protected]>
>
> Enable Kexec Handover (KHO) on LoongArch64.
>
> LoongArch has no boot FDT: the efistub passes the EFI system table and
> the command line to the core kernel directly, so the arm64 /chosen path
> (append linux,kho-fdt / linux,kho-scratch and let
> early_init_dt_check_kho() read them) does not apply.  Follow the x86
> model instead, which has no boot FDT either: carry the KHO pointer out of
> band and call kho_populate() directly.  The channel is the EFI
> configuration table entry added by the previous patch.
>
> - Kconfig: ARCH_SUPPORTS_KEXEC_HANDOVER is def_bool 64BIT.
> - machine_kexec_file.c: kho_load_data() builds a small handover blob
>   (struct linux_efi_kho_data) holding the KHO state FDT and scratch
>   addresses, and a new EFI configuration table with a
>   LINUX_EFI_KHO_TABLE_GUID entry pointing to it; both are loaded as kexec
>   segments.
> - machine_kexec.c: before jumping to the next kernel, switch the EFI
>   system table to the extended configuration table.
> - setup.c: kho_populate_from_efi() scans the configuration table for
>   LINUX_EFI_KHO_TABLE_GUID and calls kho_populate() from setup_arch(),
>   after efi_init() and before memblock_init().
>
> Handover is set up by the kexec_file_load() syscall only.  kho_load_data()
> runs from load_other_segments(), which the older kexec_load() syscall does
> not reach.  This matches x86, where KHO lives in the bzImage64 loader.
>
> Tested on a LoongArch machine booting through ACPI/UEFI.  After the kexec,
> the second kernel reports
>
>   KHO: found kexec handover data.
>
> and the two-stage test passes: luo_kexec_simple --stage 1, kexec into the
> second kernel, then luo_kexec_simple --stage 2.
>
> Co-developed-by: Kexin Liu <[email protected]>
> Signed-off-by: Kexin Liu <[email protected]>
> Signed-off-by: George Guo <[email protected]>
> ---
>  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 +++++++
>  5 files changed, 198 insertions(+)
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index d8d252325017..698828ef70f0 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -684,6 +684,9 @@ config ARCH_SUPPORTS_KEXEC
>  config ARCH_SUPPORTS_KEXEC_FILE
>         def_bool 64BIT
>
> +config ARCH_SUPPORTS_KEXEC_HANDOVER
> +       def_bool 64BIT
> +
>  config ARCH_SELECTS_KEXEC_FILE
>         def_bool 64BIT
>         depends on KEXEC_FILE
> diff --git a/arch/loongarch/include/asm/kexec.h b/arch/loongarch/include/asm/kexec.h
> index 6be136e9f0a0..2bcc8bc0d3cc 100644
> --- a/arch/loongarch/include/asm/kexec.h
> +++ b/arch/loongarch/include/asm/kexec.h
> @@ -39,6 +39,13 @@ struct kimage_arch {
>         unsigned long efi_boot;
>         unsigned long cmdline_ptr;
>         unsigned long systable_ptr;
> +#ifdef CONFIG_KEXEC_HANDOVER
> +       void *kho_data;                 /* KHO handover blob buffer (virtual) */
> +       unsigned long kho_data_mem;     /* physical address of the KHO handover blob */
> +       void *efi_tables;               /* new EFI config table buffer (virtual) */
> +       unsigned long efi_tables_mem;   /* physical address of new EFI config table */
> +       unsigned long efi_tables_cnt;   /* number of entries in new EFI config table */
> +#endif
>  };
>
>  struct kimage;
> diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
> index 1883cae93bc3..c98a5607684d 100644
> --- a/arch/loongarch/kernel/machine_kexec.c
> +++ b/arch/loongarch/kernel/machine_kexec.c
> @@ -6,6 +6,7 @@
>   */
>  #include <linux/compiler.h>
>  #include <linux/cpu.h>
> +#include <linux/efi.h>
>  #include <linux/kexec.h>
>  #include <linux/crash_dump.h>
>  #include <linux/delay.h>
> @@ -287,6 +288,21 @@ void machine_kexec(struct kimage *image)
>         pr_notice("We will call new kernel at 0x%lx\n", start_addr);
>         pr_notice("Bye ...\n");
>
> +#ifdef CONFIG_KEXEC_HANDOVER
> +       /*
> +        * KHO: switch the EFI system table to the extended configuration table
> +        * built in kho_load_data(), which carries the LINUX_EFI_KHO_TABLE_GUID
> +        * entry the next kernel reads to find the KHO handover blob.
> +        */
> +       if (internal->efi_tables_mem) {
> +               efi_system_table_t *st =
> +                       (efi_system_table_t *)TO_CACHE(systable_ptr);
> +
> +               st->tables    = internal->efi_tables_mem;
> +               st->nr_tables = internal->efi_tables_cnt;
> +       }
> +#endif
> +
>         /* Make reboot code buffer available to the boot CPU. */
>         flush_cache_all();
>
> diff --git a/arch/loongarch/kernel/machine_kexec_file.c b/arch/loongarch/kernel/machine_kexec_file.c
> index 5584b798ba46..d4c2243b6cb0 100644
> --- a/arch/loongarch/kernel/machine_kexec_file.c
> +++ b/arch/loongarch/kernel/machine_kexec_file.c
> @@ -10,6 +10,7 @@
>
>  #define pr_fmt(fmt) "kexec_file: " fmt
>
> +#include <linux/efi.h>
>  #include <linux/ioport.h>
>  #include <linux/kernel.h>
>  #include <linux/kexec.h>
> @@ -18,6 +19,7 @@
>  #include <linux/string.h>
>  #include <linux/types.h>
>  #include <linux/vmalloc.h>
> +#include <asm/addrspace.h>
>  #include <asm/bootinfo.h>
>
>  const struct kexec_file_ops * const kexec_file_loaders[] = {
> @@ -32,6 +34,13 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
>         image->elf_headers = NULL;
>         image->elf_headers_sz = 0;
>
> +#ifdef CONFIG_KEXEC_HANDOVER
> +       kfree(image->arch.kho_data);
> +       image->arch.kho_data = NULL;
> +       kvfree(image->arch.efi_tables);
> +       image->arch.efi_tables = NULL;
> +#endif
> +
>         return kexec_image_post_load_cleanup_default(image);
>  }
>
> @@ -55,6 +64,121 @@ static void cmdline_add_initrd(struct kimage *image, unsigned long *cmdline_tmpl
>         *cmdline_tmplen += initrd_strlen;
>  }
>
> +#ifdef CONFIG_KEXEC_HANDOVER
> +/*
> + * Hand the KHO state to the next kernel through a dedicated EFI configuration
> + * table entry.
> + *
> + * LoongArch has no boot FDT: the efistub passes the EFI system table and the
> + * command line to the core kernel directly.  So instead of the arm64 /chosen
> + * FDT path, build a small handover blob (struct linux_efi_kho_data) holding the
> + * KHO state FDT and scratch addresses, register it in the EFI configuration
> + * table under LINUX_EFI_KHO_TABLE_GUID, and let the next kernel read it and
> + * call kho_populate() directly.
> + *
> + * Both the blob and the extended configuration table are loaded as kexec
> + * segments; machine_kexec() switches st->tables to the new table before jumping.
> + *
> + * image->kho.fdt and image->kho.scratch are filled in by kho_fill_kimage()
> + * before the arch loader runs, so they are valid here.
> + */
> +static int kho_load_data(struct kimage *image)
> +{
> +       struct linux_efi_kho_data *kho;
> +       efi_system_table_t *st;
> +       efi_config_table_t *ct, *new_ct;
> +       size_t old_sz, new_sz;
> +       struct kexec_buf kbuf = {
> +               .image          = image,
> +               .buf_min        = 0,
> +               .buf_max        = ULONG_MAX,
> +               .top_down       = true,
> +       };
> +       int ret;
> +
> +       if (!image->kho.fdt || !image->kho.scratch)
> +               return 0;
> +
> +       if (!fw_arg2) {
> +               pr_err("KHO requires an EFI boot, no EFI system table found\n");
> +               return -EINVAL;
> +       }
This check is unnecessary, if no EFI system table, you cannot boot
your system, and have no chance for kexec.

> +
> +       /* Build the handover blob and load it as a kexec segment. */
> +       kho = kzalloc(sizeof(*kho), GFP_KERNEL);
> +       if (!kho)
> +               return -ENOMEM;
> +
> +       kho->fdt_addr     = image->kho.fdt;
> +       kho->fdt_size     = PAGE_SIZE;
> +       kho->scratch_addr = image->kho.scratch->mem;
> +       kho->scratch_size = image->kho.scratch->memsz;
> +
> +       kbuf.buffer     = kho;
> +       kbuf.bufsz      = sizeof(*kho);
> +       kbuf.memsz      = sizeof(*kho);
> +       kbuf.buf_align  = sizeof(u64);
> +       kbuf.mem        = KEXEC_BUF_MEM_UNKNOWN;
> +
> +       ret = kexec_add_buffer(&kbuf);
> +       if (ret) {
> +               kfree(kho);
> +               return ret;
> +       }
> +       image->arch.kho_data     = kho;
> +       image->arch.kho_data_mem = kbuf.mem;
> +
> +       kexec_dprintk("Loaded KHO handover blob at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
> +                     image->arch.kho_data_mem, kbuf.bufsz, kbuf.memsz);
> +       kexec_dprintk("KHO fdt at 0x%llx, scratch at 0x%llx size 0x%llx\n",
> +                     kho->fdt_addr, kho->scratch_addr, kho->scratch_size);
> +
> +       /*
> +        * Build a new EFI configuration table with a LINUX_EFI_KHO_TABLE_GUID
> +        * entry appended, pointing at the handover blob, and load it as a kexec
> +        * segment.  machine_kexec() updates st->tables / st->nr_tables to point
> +        * to it before jumping.
> +        *
> +        * fw_arg2 is the EFI system table physical address passed by the
> +        * firmware/bootloader.  Use it directly because image->arch.systable_ptr
> +        * is set later in machine_kexec_prepare(), which runs after this.
> +        */
> +       st = (efi_system_table_t *)TO_CACHE(fw_arg2);
> +       ct = (efi_config_table_t *)TO_CACHE((unsigned long)st->tables);
> +       old_sz = st->nr_tables * sizeof(efi_config_table_t);
> +       new_sz = old_sz + sizeof(efi_config_table_t);
> +
> +       new_ct = kvmalloc(new_sz, GFP_KERNEL);
> +       if (!new_ct)
> +               return -ENOMEM;
> +
> +       memcpy(new_ct, ct, old_sz);
> +       new_ct[st->nr_tables].guid  = LINUX_EFI_KHO_TABLE_GUID;
> +       new_ct[st->nr_tables].table = (void *)image->arch.kho_data_mem;
> +
> +       kbuf.buffer     = new_ct;
> +       kbuf.bufsz      = new_sz;
> +       kbuf.memsz      = new_sz;
> +       kbuf.buf_align  = sizeof(void *);
> +       kbuf.mem        = KEXEC_BUF_MEM_UNKNOWN;
> +
> +       ret = kexec_add_buffer(&kbuf);
> +       if (ret) {
> +               kvfree(new_ct);
> +               return ret;
> +       }
> +       image->arch.efi_tables     = new_ct;
> +       image->arch.efi_tables_mem = kbuf.mem;
> +       image->arch.efi_tables_cnt = st->nr_tables + 1;
> +
> +       kexec_dprintk("Loaded EFI config table at 0x%lx bufsz=0x%lx memsz=0x%lx nr_tables=%lu\n",
> +                     image->arch.efi_tables_mem, kbuf.bufsz, kbuf.memsz,
> +                     image->arch.efi_tables_cnt);
> +
> +       return 0;
> +}
> +#endif
> +
>  #ifdef CONFIG_CRASH_DUMP
>
>  static int prepare_elf_headers(void **addr, unsigned long *sz)
> @@ -220,6 +344,13 @@ int load_other_segments(struct kimage *image,
>                 cmdline_add_initrd(image, &cmdline_tmplen, modified_cmdline, initrd_load_addr);
>         }
>
> +#ifdef CONFIG_KEXEC_HANDOVER
> +       /* Load the KHO handover blob and the extended EFI configuration table */
> +       ret = kho_load_data(image);
> +       if (ret)
> +               goto out_err;
> +#endif
> +
>         if (cmdline_len + cmdline_tmplen > COMMAND_LINE_SIZE) {
>                 pr_err("Appending command line exceeds COMMAND_LINE_SIZE\n");
>                 ret = -EINVAL;
> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> index 6fa4a22a58fd..1e2fbf37aecf 100644
> --- a/arch/loongarch/kernel/setup.c
> +++ b/arch/loongarch/kernel/setup.c
> @@ -20,6 +20,7 @@
>  #include <linux/initrd.h>
>  #include <linux/ioport.h>
>  #include <linux/kexec.h>
> +#include <linux/kexec_handover.h>
>  #include <linux/crash_dump.h>
>  #include <linux/root_dev.h>
>  #include <linux/console.h>
> @@ -280,6 +281,45 @@ static void __init arch_reserve_crashkernel(void)
>         reserve_crashkernel_generic(crash_size, crash_base, low_size, high);
>  }
>
> +#ifdef CONFIG_KEXEC_HANDOVER
> +/*
> + * On a KHO kexec boot the previous kernel registered a handover blob in the EFI
> + * configuration table under LINUX_EFI_KHO_TABLE_GUID (see
> + * arch/loongarch/kernel/machine_kexec_file.c).  Scan the configuration table
> + * for it, read the KHO state FDT and scratch addresses, and hand them to the
> + * KHO core.  fw_arg2 is the EFI system table physical address.
> + *
> + * This runs from setup_arch(), after efi_init() and before memblock_init(),
> + * which is where the generic reader early_init_dt_check_kho() would call
> + * kho_populate().
> + */
> +static void __init kho_populate_from_efi(void)
> +{
> +       efi_system_table_t *st;
> +       efi_config_table_t *ct;
> +       struct linux_efi_kho_data *kho;
> +       unsigned long i;
> +
> +       if (!fw_arg2)
> +               return;
> +
> +       st = (efi_system_table_t *)TO_CACHE(fw_arg2);
> +       ct = (efi_config_table_t *)TO_CACHE((unsigned long)st->tables);
> +
> +       for (i = 0; i < st->nr_tables; i++) {
> +               if (efi_guidcmp(ct[i].guid, LINUX_EFI_KHO_TABLE_GUID))
> +                       continue;
> +
> +               kho = (struct linux_efi_kho_data *)TO_CACHE((unsigned long)ct[i].table);
> +               kho_populate(kho->fdt_addr, kho->fdt_size,
> +                            kho->scratch_addr, kho->scratch_size);
> +               break;
> +       }
> +}
If you do this in efi.c, you can significantly simplify the code. By
defining the KHO table in arch_tables[], you almost only need to call
kho_populate() at the end of efi_init().

Huacai

> +#else
> +static void __init kho_populate_from_efi(void) { }
> +#endif
> +
>  static void __init fdt_setup(void)
>  {
>  #ifdef CONFIG_OF_EARLY_FLATTREE
> @@ -599,6 +639,7 @@ void __init setup_arch(char **cmdline_p)
>
>         init_environ();
>         efi_init();
> +       kho_populate_from_efi();
>         fdt_setup();
>         memblock_init();
>         pagetable_init();
> --
> 2.53.0
>