[PATCH v2 1/4] LoongArch: kexec: add KHO support for FDT-based systems
George Guo
dongtai.guo at linux.dev
Fri May 29 07:32:35 PDT 2026
From: George Guo <guodongtai at kylinos.cn>
Enable Kexec Handover (KHO) on LoongArch64 for FDT-based systems.
- Kconfig: select ARCH_SUPPORTS_KEXEC_HANDOVER for CONFIG_64BIT
- kexec.h: add fdt/fdt_mem fields to kimage_arch to hold the KHO FDT
kexec segment virtual and physical addresses
- machine_kexec_file.c: add kho_load_fdt() which copies the running
kernel's FDT (initial_boot_params), appends linux,kho-fdt and
linux,kho-scratch properties to /chosen, and loads the result as a
kexec segment; called from load_other_segments(). Returns -EINVAL
when initial_boot_params is NULL (ACPI-only boot) since that path
requires separate handling.
- machine_kexec.c: before jumping to the new kernel, update the
DEVICE_TREE_GUID entry in the EFI config table to point to the KHO
FDT segment so the second kernel finds it via efi_fdt_pointer() and
early_init_dt_check_kho() calls kho_populate()
Co-developed-by: Kexin Liu <liukexin at kylinos.cn>
Signed-off-by: Kexin Liu <liukexin at kylinos.cn>
Signed-off-by: George Guo <guodongtai at kylinos.cn>
---
arch/loongarch/Kconfig | 3 +
arch/loongarch/include/asm/kexec.h | 4 +
arch/loongarch/kernel/machine_kexec.c | 27 +++++
arch/loongarch/kernel/machine_kexec_file.c | 118 +++++++++++++++++++++
4 files changed, 152 insertions(+)
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 606597da46b8..d494418545f5 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 209fa43222e1..adf54bfcdd49 100644
--- a/arch/loongarch/include/asm/kexec.h
+++ b/arch/loongarch/include/asm/kexec.h
@@ -39,6 +39,10 @@ struct kimage_arch {
unsigned long efi_boot;
unsigned long cmdline_ptr;
unsigned long systable_ptr;
+#ifdef CONFIG_KEXEC_HANDOVER
+ void *fdt; /* virtual address of KHO FDT segment buffer */
+ unsigned long fdt_mem; /* physical address of KHO FDT segment */
+#endif
};
#ifdef CONFIG_KEXEC_FILE
diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
index d7fafda1d541..130f1adfa515 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>
@@ -284,6 +285,32 @@ 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
+ /*
+ * Point the EFI FDTPTR config table entry at the modified FDT so the
+ * second kernel picks up the linux,kho-fdt and linux,kho-scratch
+ * properties via early_init_dt_check_kho().
+ */
+ if (internal->fdt_mem) {
+ /*
+ * FDT-based system: DEVICE_TREE_GUID already exists in the EFI
+ * config table; just update its pointer to our KHO FDT.
+ */
+ efi_system_table_t *st =
+ (efi_system_table_t *)TO_CACHE(systable_ptr);
+ efi_config_table_t *ct =
+ (efi_config_table_t *)TO_CACHE((unsigned long)st->tables);
+ unsigned long i;
+
+ for (i = 0; i < st->nr_tables; i++) {
+ if (!efi_guidcmp(ct[i].guid, DEVICE_TREE_GUID)) {
+ ct[i].table = (void *)internal->fdt_mem;
+ break;
+ }
+ }
+ }
+#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..bf1e8c1c7e70 100644
--- a/arch/loongarch/kernel/machine_kexec_file.c
+++ b/arch/loongarch/kernel/machine_kexec_file.c
@@ -13,7 +13,9 @@
#include <linux/ioport.h>
#include <linux/kernel.h>
#include <linux/kexec.h>
+#include <linux/libfdt.h>
#include <linux/memblock.h>
+#include <linux/of_fdt.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/types.h>
@@ -32,6 +34,11 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
image->elf_headers = NULL;
image->elf_headers_sz = 0;
+#ifdef CONFIG_KEXEC_HANDOVER
+ kvfree(image->arch.fdt);
+ image->arch.fdt = NULL;
+#endif
+
return kexec_image_post_load_cleanup_default(image);
}
@@ -55,6 +62,111 @@ static void cmdline_add_initrd(struct kimage *image, unsigned long *cmdline_tmpl
*cmdline_tmplen += initrd_strlen;
}
+#ifdef CONFIG_KEXEC_HANDOVER
+/*
+ * Add KHO metadata to an FDT /chosen node and load the FDT as a kexec
+ * segment. The second kernel reads linux,kho-fdt and linux,kho-scratch
+ * from /chosen via early_init_dt_check_kho() and calls kho_populate().
+ *
+ */
+static int kho_load_fdt(struct kimage *image)
+{
+ void *fdt;
+ int ret, chosen_node;
+ size_t fdt_size;
+ struct kexec_buf kbuf = {
+ .image = image,
+ .buf_min = 0,
+ .buf_max = ULONG_MAX,
+ .top_down = true,
+ };
+
+ if (!image->kho.fdt || !image->kho.scratch)
+ return 0;
+
+ if (initial_boot_params) {
+ /*
+ * FDT boot: copy the running kernel's FDT and append KHO
+ * properties to /chosen.
+ */
+
+ /*
+ * Only two KHO properties are added to /chosen (linux,kho-fdt
+ * and linux,kho-scratch), so SZ_1K of extra space is
+ * sufficient.
+ */
+ fdt_size = fdt_totalsize(initial_boot_params) + SZ_1K;
+ fdt = kvmalloc(fdt_size, GFP_KERNEL);
+ if (!fdt)
+ return -ENOMEM;
+
+ ret = fdt_open_into(initial_boot_params, fdt, fdt_size);
+ if (ret < 0) {
+ pr_err("Failed to open FDT: %d\n", ret);
+ goto out_free;
+ }
+
+ chosen_node = fdt_path_offset(fdt, "/chosen");
+ if (chosen_node == -FDT_ERR_NOTFOUND) {
+ pr_debug("No /chosen node in FDT, creating one\n");
+ chosen_node = fdt_add_subnode(fdt,
+ fdt_path_offset(fdt, "/"),
+ "chosen");
+ }
+ if (chosen_node < 0) {
+ ret = chosen_node;
+ goto out_free;
+ }
+
+ /* Remove stale KHO properties left by a previous kexec load */
+ fdt_delprop(fdt, chosen_node, "linux,kho-fdt");
+ fdt_delprop(fdt, chosen_node, "linux,kho-scratch");
+
+ ret = fdt_appendprop_addrrange(fdt, 0, chosen_node,
+ "linux,kho-fdt",
+ image->kho.fdt, PAGE_SIZE);
+ if (ret)
+ goto out_free;
+
+ ret = fdt_appendprop_addrrange(fdt, 0, chosen_node,
+ "linux,kho-scratch",
+ image->kho.scratch->mem,
+ image->kho.scratch->bufsz);
+ if (ret)
+ goto out_free;
+
+ /*
+ * Shrink totalsize to the actual data size so the kexec segment
+ * allocated by kexec_add_buffer() covers only the packed FDT data.
+ * The slack added above for property insertion is part of the
+ * kvmalloc'd buffer, which is freed by kimage_file_post_load_cleanup()
+ * once the kexec image has been loaded.
+ */
+ fdt_pack(fdt);
+
+ kbuf.buffer = fdt;
+ kbuf.bufsz = fdt_totalsize(fdt);
+ kbuf.memsz = kbuf.bufsz;
+ kbuf.buf_align = PAGE_SIZE;
+ kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
+
+ ret = kexec_add_buffer(&kbuf);
+ if (ret)
+ goto out_free;
+
+ image->arch.fdt = fdt;
+ image->arch.fdt_mem = kbuf.mem;
+ return 0;
+ } else {
+ return -EINVAL;
+ }
+
+out_free:
+ kvfree(fdt);
+ return ret;
+}
+#endif
+
#ifdef CONFIG_CRASH_DUMP
static int prepare_elf_headers(void **addr, unsigned long *sz)
@@ -230,6 +342,12 @@ int load_other_segments(struct kimage *image,
cmdline = modified_cmdline;
image->arch.cmdline_ptr = (unsigned long)cmdline;
+#ifdef CONFIG_KEXEC_HANDOVER
+ ret = kho_load_fdt(image);
+ if (ret)
+ goto out_err;
+#endif
+
return 0;
out_err:
--
2.25.1
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