LoongArch: kdump: Add memory reservation for old kernel

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I736HO

--------------------------------

After moving the old kernel memory reservation to elfcorehdr operation, avoid
the elfcorehdr space from being destroyed.
Signed-off-by: NYouling Tang <tangyouling@loongson.cn>
Change-Id: I94d5c38e24dd6d3ab3fddc3945580780d81e6922

arch/loongarch/kernel/setup.c

@@ -65,6 +65,8 @@ EXPORT_SYMBOL(cpu_data);
 struct loongson_board_info b_info;
 static const char dmi_empty_string[] = "        ";
 
+static phys_addr_t crashmem_start, crashmem_size;
+
 /*
  * Setup information
  *
@@ -180,16 +182,6 @@ static int __init early_parse_mem(char *p)
 		return -EINVAL;
 	}
 
-	/*
-	 * If a user specifies memory size, we
-	 * blow away any automatically generated
-	 * size.
-	 */
-	if (usermem == 0) {
-		usermem = 1;
-		memblock_remove(memblock_start_of_DRAM(),
-			memblock_end_of_DRAM() - memblock_start_of_DRAM());
-	}
 	start = 0;
 	size = memparse(p, &p);
 	if (*p == '@')
@@ -199,6 +191,23 @@ static int __init early_parse_mem(char *p)
 		return -EINVAL;
 	}
 
+	/*
+	 * If a user specifies memory size, we
+	 * blow away any automatically generated
+	 * size.
+	 */
+	if (usermem == 0) {
+		usermem = 1;
+		if (!strstr(boot_command_line, "elfcorehdr")) {
+			memblock_remove(memblock_start_of_DRAM(),
+				memblock_end_of_DRAM() - memblock_start_of_DRAM());
+		} else {
+			crashmem_start = start;
+			crashmem_size = size;
+			return 0;
+		}
+	}
+
 	if (!IS_ENABLED(CONFIG_NUMA))
 		memblock_add(start, size);
 	else
@@ -282,10 +291,26 @@ static void __init arch_parse_crashkernel(void)
 #endif
 }
 
+/*
+ * After the kdump operation is performed to enter the capture kernel, the
+ * memory area used by the previous production kernel should be reserved to
+ * avoid destroy to the captured data.
+ */
+static void reserve_oldmem_region(void)
+{
+#ifdef CONFIG_CRASH_DUMP
+	if (!is_kdump_kernel())
+		return;
+
+	memblock_cap_memory_range(crashmem_start, crashmem_size);
+#endif
+}
+
 void __init platform_init(void)
 {
 	arch_reserve_vmcore();
 	arch_parse_crashkernel();
+	reserve_oldmem_region();
 
 #ifdef CONFIG_ACPI_TABLE_UPGRADE
 	acpi_table_upgrade();