[PATCH v7 10/18] arm64: add KHO support

Changyuan Lyu
2025-05-01T22:55:29Z

From: Alexander Graf <graf@amazon.com>

We now have all bits in place to support KHO kexecs. Add awareness of
KHO in the kexec file as well as boot path for arm64 and adds the
respective kconfig option to the architecture so that it can use KHO
successfully.

Changes to the "chosen" node have been sent to
https://github.com/devicetree-org/dt-schema/pull/158.

Signed-off-by: Alexander Graf <graf@amazon.com>
Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Co-developed-by: Changyuan Lyu <changyuanl@google.com>
Signed-off-by: Changyuan Lyu <changyuanl@google.com>
---
arch/arm64/Kconfig | 3 +++
drivers/of/fdt.c | 34 ++++++++++++++++++++++++++++++++++
drivers/of/kexec.c | 42 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 79 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a182295e6f08b..34c79f4fee3f9 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1602,6 +1602,9 @@ config ARCH_SUPPORTS_KEXEC_IMAGE_VERIFY_SIG
config ARCH_DEFAULT_KEXEC_IMAGE_VERIFY_SIG
def_bool y

+config ARCH_SUPPORTS_KEXEC_HANDOVER
+ def_bool y
+
config ARCH_SUPPORTS_CRASH_DUMP
def_bool y

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index aedd0e2dcd890..0edd639898a63 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -25,6 +25,7 @@
#include <linux/serial_core.h>
#include <linux/sysfs.h>
#include <linux/random.h>
+#include <linux/kexec_handover.h>

#include <asm/setup.h> /* for COMMAND_LINE_SIZE */
#include <asm/page.h>
@@ -875,6 +876,36 @@ void __init early_init_dt_check_for_usable_mem_range(void)
memblock_add(rgn[i].base, rgn[i].size);
}

+/**
+ * early_init_dt_check_kho - Decode info required for kexec handover from DT
+ */
+static void __init early_init_dt_check_kho(void)
+{
+ unsigned long node = chosen_node_offset;
+ u64 fdt_start, fdt_size, scratch_start, scratch_size;
+ const __be32 *p;
+ int l;
+
+ if (!IS_ENABLED(CONFIG_KEXEC_HANDOVER) || (long)node < 0)
+ return;
+
+ p = of_get_flat_dt_prop(node, "linux,kho-fdt", &l);
+ if (l != (dt_root_addr_cells + dt_root_size_cells) * sizeof(__be32))
+ return;
+
+ fdt_start = dt_mem_next_cell(dt_root_addr_cells, &p);
+ fdt_size = dt_mem_next_cell(dt_root_addr_cells, &p);
+
+ p = of_get_flat_dt_prop(node, "linux,kho-scratch", &l);
+ if (l != (dt_root_addr_cells + dt_root_size_cells) * sizeof(__be32))
+ return;
+
+ scratch_start = dt_mem_next_cell(dt_root_addr_cells, &p);
+ scratch_size = dt_mem_next_cell(dt_root_addr_cells, &p);
+
+ kho_populate(fdt_start, fdt_size, scratch_start, scratch_size);
+}
+
#ifdef CONFIG_SERIAL_EARLYCON

int __init early_init_dt_scan_chosen_stdout(void)
@@ -1169,6 +1200,9 @@ void __init early_init_dt_scan_nodes(void)

/* Handle linux,usable-memory-range property */
early_init_dt_check_for_usable_mem_range();
+
+ /* Handle kexec handover */
+ early_init_dt_check_kho();
}

bool __init early_init_dt_scan(void *dt_virt, phys_addr_t dt_phys)
diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
index 5b924597a4deb..1ee2d31816aeb 100644
--- a/drivers/of/kexec.c
+++ b/drivers/of/kexec.c
@@ -264,6 +264,43 @@ static inline int setup_ima_buffer(const struct kimage *image, void *fdt,
}
#endif /* CONFIG_IMA_KEXEC */

+static int kho_add_chosen(const struct kimage *image, void *fdt, int chosen_node)
+{
+ int ret = 0;
+#ifdef CONFIG_KEXEC_HANDOVER
+ phys_addr_t fdt_mem = 0;
+ phys_addr_t fdt_len = 0;
+ phys_addr_t scratch_mem = 0;
+ phys_addr_t scratch_len = 0;
+
+ ret = fdt_delprop(fdt, chosen_node, "linux,kho-fdt");
+ if (ret && ret != -FDT_ERR_NOTFOUND)
+ return ret;
+ ret = fdt_delprop(fdt, chosen_node, "linux,kho-scratch");
+ if (ret && ret != -FDT_ERR_NOTFOUND)
+ return ret;
+
+ if (!image->kho.fdt || !image->kho.scratch)
+ return 0;
+
+ fdt_mem = image->kho.fdt;
+ fdt_len = PAGE_SIZE;
+ scratch_mem = image->kho.scratch->mem;
+ scratch_len = image->kho.scratch->bufsz;
+
+ pr_debug("Adding kho metadata to DT");
+
+ ret = fdt_appendprop_addrrange(fdt, 0, chosen_node, "linux,kho-fdt",
+ fdt_mem, fdt_len);
+ if (ret)
+ return ret;
+ ret = fdt_appendprop_addrrange(fdt, 0, chosen_node, "linux,kho-scratch",
+ scratch_mem, scratch_len);
+
+#endif /* CONFIG_KEXEC_HANDOVER */
+ return ret;
+}
+
/*
* of_kexec_alloc_and_setup_fdt - Alloc and setup a new Flattened Device Tree
*
@@ -414,6 +451,11 @@ void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
#endif
}

+ /* Add kho metadata if this is a KHO image */
+ ret = kho_add_chosen(image, fdt, chosen_node);
+ if (ret)
+ goto out;
+
/* add bootargs */
if (cmdline) {
ret = fdt_setprop_string(fdt, chosen_node, "bootargs", cmdline);
--
2.49.0.906.g1f30a19c02-goog