LoongArch: Add crash dump support for kexec_file

Enabling crash dump (kdump) includes:
- Prepare contents of ELF header of a core dump file, /proc/vmcore,
  using crash_prepare_elf64_headers().
- Add "mem=size@start" parameter to the command line and pass it to the
  capture kernel.  Limit the runtime memory area of the captured kernel
  to avoid disrupting the production kernel's runtime state.
- Add "elfcorehdr=size@start" parameter to the cmdline.

The basic usage for kdump (add the cmdline parameter crashkernel=512M
to grub.cfg for production kernel):

1) Load capture kernel image (vmlinux.efi or vmlinux can both be used):
 # kexec -s -p vmlinuz.efi --initrd=initrd.img --reuse-cmdline

2) Do something to crash, like:
 # echo c > /proc/sysrq-trigger

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

Author: tangyouling

arch/loongarch/kernel/machine_kexec_file.c

@@ -55,6 +55,81 @@ static void cmdline_add_initrd(struct kimage *image, unsigned long *cmdline_tmpl
 	*cmdline_tmplen += initrd_strlen;
 }
 
+#ifdef CONFIG_CRASH_DUMP
+
+static int prepare_elf_headers(void **addr, unsigned long *sz)
+{
+	int ret, nr_ranges;
+	uint64_t i;
+	phys_addr_t start, end;
+	struct crash_mem *cmem;
+
+	nr_ranges = 2; /* for exclusion of crashkernel region */
+	for_each_mem_range(i, &start, &end)
+		nr_ranges++;
+
+	cmem = kmalloc(struct_size(cmem, ranges, nr_ranges), GFP_KERNEL);
+	if (!cmem)
+		return -ENOMEM;
+
+	cmem->max_nr_ranges = nr_ranges;
+	cmem->nr_ranges = 0;
+	for_each_mem_range(i, &start, &end) {
+		cmem->ranges[cmem->nr_ranges].start = start;
+		cmem->ranges[cmem->nr_ranges].end = end - 1;
+		cmem->nr_ranges++;
+	}
+
+	/* Exclude crashkernel region */
+	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
+	if (ret < 0)
+		goto out;
+
+	if (crashk_low_res.end) {
+		ret = crash_exclude_mem_range(cmem, crashk_low_res.start, crashk_low_res.end);
+		if (ret < 0)
+			goto out;
+	}
+
+	ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
+
+out:
+	kfree(cmem);
+	return ret;
+}
+
+/*
+ * Add the "mem=size@start" command line parameter to command line, indicating the
+ * memory region the new kernel can use to boot into.
+ */
+static void cmdline_add_mem(unsigned long *cmdline_tmplen, char *modified_cmdline)
+{
+	int mem_strlen = 0;
+
+	mem_strlen = sprintf(modified_cmdline + (*cmdline_tmplen), "mem=0x%llx@0x%llx ",
+		crashk_res.end - crashk_res.start + 1, crashk_res.start);
+	*cmdline_tmplen += mem_strlen;
+
+	if (crashk_low_res.end) {
+		mem_strlen = sprintf(modified_cmdline + (*cmdline_tmplen), "mem=0x%llx@0x%llx ",
+			crashk_low_res.end - crashk_low_res.start + 1, crashk_low_res.start);
+		*cmdline_tmplen += mem_strlen;
+	}
+}
+
+/* Add the "elfcorehdr=size@start" command line parameter to command line. */
+static void cmdline_add_elfcorehdr(struct kimage *image, unsigned long *cmdline_tmplen,
+				   char *modified_cmdline, unsigned long elfcorehdr_sz)
+{
+	int elfcorehdr_strlen = 0;
+
+	elfcorehdr_strlen = sprintf(modified_cmdline + (*cmdline_tmplen), "elfcorehdr=0x%lx@0x%lx ",
+		elfcorehdr_sz, image->elf_load_addr);
+	*cmdline_tmplen += elfcorehdr_strlen;
+}
+
+#endif
+
 /*
  * Try to add the initrd to the image. If it is not possible to find valid
  * locations, this function will undo changes to the image and return non zero.
@@ -82,6 +157,46 @@ int load_other_segments(struct kimage *image,
 	/* Ensure it's null terminated */
 	modified_cmdline[COMMAND_LINE_SIZE - 1] = '\0';
 
+#ifdef CONFIG_CRASH_DUMP
+	/* Load elf core header */
+	if (image->type == KEXEC_TYPE_CRASH) {
+		void *headers;
+		unsigned long headers_sz;
+
+		ret = prepare_elf_headers(&headers, &headers_sz);
+		if (ret < 0) {
+			pr_err("Preparing elf core header failed\n");
+			goto out_err;
+		}
+
+		kbuf.buffer = headers;
+		kbuf.bufsz = headers_sz;
+		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
+		kbuf.memsz = headers_sz;
+		kbuf.buf_align = SZ_64K; /* largest supported page size */
+		kbuf.buf_max = ULONG_MAX;
+		kbuf.top_down = true;
+
+		ret = kexec_add_buffer(&kbuf);
+		if (ret < 0) {
+			vfree(headers);
+			goto out_err;
+		}
+		image->elf_headers = headers;
+		image->elf_load_addr = kbuf.mem;
+		image->elf_headers_sz = headers_sz;
+
+		kexec_dprintk("Loaded elf core header at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
+			      image->elf_load_addr, kbuf.bufsz, kbuf.memsz);
+
+		/* Add the mem=size@start parameter to the command line */
+		cmdline_add_mem(&cmdline_tmplen, modified_cmdline);
+
+		/* Add the elfcorehdr=size@start parameter to the command line */
+		cmdline_add_elfcorehdr(image, &cmdline_tmplen, modified_cmdline, headers_sz);
+	}
+#endif
+
 	/* Load initrd */
 	if (initrd) {
 		kbuf.buffer = initrd;