LoongArch: Add EFI binary support for kexec_file

This patch creates kexec_efi_ops to load EFI binary file for
kexec_file_load() syscall.

The efi_kexec_load() as two parts:
- the first part loads the kernel image (vmlinuz.efi or vmlinux.efi)
- the second part loads other segments (e.g: initrd, cmdline, etc)

Currently, pez (vmlinuz.efi) and pei (vmlinux.efi) format images are
supported.

The basic usage (vmlinuz.efi or vmlinux.efi):

1) Load second kernel image:
 # kexec -s -l vmlinuz.efi --initrd=initrd.img --reuse-cmdline

2) Startup second kernel:
 # kexec -e

Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/image.h

@@ -33,6 +33,20 @@ struct loongarch_image_header {
 	uint32_t pe_header;
 };
 
+/*
+ * loongarch_header_check_dos_sig - Helper to check the header
+ *
+ * Returns true (non-zero) if 'MZ' signature is found.
+ */
+
+static inline int loongarch_header_check_dos_sig(const struct loongarch_image_header *h)
+{
+	if (!h)
+		return 0;
+
+	return (h->dos_sig[0] == 'M' && h->dos_sig[1] == 'Z');
+}
+
 #endif /* __ASSEMBLER__ */
 
 #endif /* __ASM_IMAGE_H */

arch/loongarch/include/asm/kexec.h

@@ -42,6 +42,7 @@ struct kimage_arch {
 };
 
 #ifdef CONFIG_KEXEC_FILE
+extern const struct kexec_file_ops kexec_efi_ops;
 
 int arch_kimage_file_post_load_cleanup(struct kimage *image);
 #define arch_kimage_file_post_load_cleanup arch_kimage_file_post_load_cleanup

arch/loongarch/kernel/Makefile

@@ -62,7 +62,7 @@ obj-$(CONFIG_MAGIC_SYSRQ)	+= sysrq.o
 obj-$(CONFIG_RELOCATABLE)	+= relocate.o
 
 obj-$(CONFIG_KEXEC_CORE)	+= machine_kexec.o relocate_kernel.o
-obj-$(CONFIG_KEXEC_FILE)	+= machine_kexec_file.o
+obj-$(CONFIG_KEXEC_FILE)	+= machine_kexec_file.o kexec_efi.o
 obj-$(CONFIG_CRASH_DUMP)	+= crash_dump.o
 
 obj-$(CONFIG_UNWINDER_GUESS)	+= unwind_guess.o

arch/loongarch/kernel/kexec_efi.c

@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Load EFI vmlinux file for the kexec_file_load syscall.
+ *
+ * Author: Youling Tang <tangyouling@kylinos.cn>
+ * Copyright (C) 2025 KylinSoft Corporation.
+ */
+
+#define pr_fmt(fmt)	"kexec_file(EFI): " fmt
+
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/kexec.h>
+#include <linux/pe.h>
+#include <linux/string.h>
+#include <asm/byteorder.h>
+#include <asm/cpufeature.h>
+#include <asm/image.h>
+
+static int efi_kexec_probe(const char *kernel_buf, unsigned long kernel_len)
+{
+	const struct loongarch_image_header *h = (const struct loongarch_image_header *)kernel_buf;
+
+	if (!h || (kernel_len < sizeof(*h))) {
+		kexec_dprintk("No LoongArch image header.\n");
+		return -EINVAL;
+	}
+
+	if (!loongarch_header_check_dos_sig(h)) {
+		kexec_dprintk("No LoongArch PE image header.\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void *efi_kexec_load(struct kimage *image,
+				char *kernel, unsigned long kernel_len,
+				char *initrd, unsigned long initrd_len,
+				char *cmdline, unsigned long cmdline_len)
+{
+	int ret;
+	unsigned long text_offset, kernel_segment_number;
+	struct kexec_buf kbuf;
+	struct kexec_segment *kernel_segment;
+	struct loongarch_image_header *h;
+
+	h = (struct loongarch_image_header *)kernel;
+	if (!h->kernel_asize)
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * Load the kernel
+	 * FIXME: Non-relocatable kernel rejected for kexec_file (require CONFIG_RELOCATABLE)
+	 */
+	kbuf.image = image;
+	kbuf.buf_max = ULONG_MAX;
+	kbuf.top_down = false;
+
+	kbuf.buffer = kernel;
+	kbuf.bufsz = kernel_len;
+	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
+	kbuf.memsz = le64_to_cpu(h->kernel_asize);
+	text_offset = le64_to_cpu(h->text_offset);
+	kbuf.buf_min = text_offset;
+	kbuf.buf_align = SZ_2M;
+
+	kernel_segment_number = image->nr_segments;
+
+	/*
+	 * The location of the kernel segment may make it impossible to
+	 * satisfy the other segment requirements, so we try repeatedly
+	 * to find a location that will work.
+	 */
+	while ((ret = kexec_add_buffer(&kbuf)) == 0) {
+		/* Try to load additional data */
+		kernel_segment = &image->segment[kernel_segment_number];
+		ret = load_other_segments(image, kernel_segment->mem,
+					  kernel_segment->memsz, initrd,
+					  initrd_len, cmdline, cmdline_len);
+		if (!ret)
+			break;
+
+		/*
+		 * We couldn't find space for the other segments; erase the
+		 * kernel segment and try the next available hole.
+		 */
+		image->nr_segments -= 1;
+		kbuf.buf_min = kernel_segment->mem + kernel_segment->memsz;
+		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
+	}
+
+	if (ret < 0) {
+		pr_err("Could not find any suitable kernel location!");
+		return ERR_PTR(ret);
+	}
+
+	kernel_segment = &image->segment[kernel_segment_number];
+
+	/* Make sure the second kernel jumps to the correct "kernel_entry" */
+	image->start = kernel_segment->mem + h->kernel_entry - text_offset;
+
+	kexec_dprintk("Loaded kernel at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
+		      kernel_segment->mem, kbuf.bufsz, kernel_segment->memsz);
+
+	return NULL;
+}
+
+const struct kexec_file_ops kexec_efi_ops = {
+	.probe = efi_kexec_probe,
+	.load = efi_kexec_load,
+};

arch/loongarch/kernel/machine_kexec_file.c

@@ -21,6 +21,7 @@
 #include <asm/bootinfo.h>
 
 const struct kexec_file_ops * const kexec_file_loaders[] = {
+	&kexec_efi_ops,
 	NULL
 };