mips: reserve elfcorehdr

/proc/vmcore wasn't showing up in kdump kernels.  It turns that that
for Octeon, the memory used by elfcorehdr wasn't being set aside
properly and it was getting clobbered before /proc/vmcore could get
it.  So reserve the memory if it shows up in a memory area managed
by the kernel.
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Acked-by: David Daney  <ddaney@caviumnetworks.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Patchwork: http://patchwork.linux-mips.org/patch/4936/

arch/mips/kernel/setup.c

@@ -480,6 +480,37 @@ static int __init early_parse_mem(char *p)
 }
 early_param("mem", early_parse_mem);
 
+#ifdef CONFIG_PROC_VMCORE
+unsigned long setup_elfcorehdr, setup_elfcorehdr_size;
+static int __init early_parse_elfcorehdr(char *p)
+{
+	int i;
+
+	setup_elfcorehdr = memparse(p, &p);
+
+	for (i = 0; i < boot_mem_map.nr_map; i++) {
+		unsigned long start = boot_mem_map.map[i].addr;
+		unsigned long end = (boot_mem_map.map[i].addr +
+				     boot_mem_map.map[i].size);
+		if (setup_elfcorehdr >= start && setup_elfcorehdr < end) {
+			/*
+			 * Reserve from the elf core header to the end of
+			 * the memory segment, that should all be kdump
+			 * reserved memory.
+			 */
+			setup_elfcorehdr_size = end - setup_elfcorehdr;
+			break;
+		}
+	}
+	/*
+	 * If we don't find it in the memory map, then we shouldn't
+	 * have to worry about it, as the new kernel won't use it.
+	 */
+	return 0;
+}
+early_param("elfcorehdr", early_parse_elfcorehdr);
+#endif
+
 static void __init arch_mem_addpart(phys_t mem, phys_t end, int type)
 {
 	phys_t size;
@@ -547,6 +578,14 @@ static void __init arch_mem_init(char **cmdline_p)
 	}
 
 	bootmem_init();
+#ifdef CONFIG_PROC_VMCORE
+	if (setup_elfcorehdr && setup_elfcorehdr_size) {
+		printk(KERN_INFO "kdump reserved memory at %lx-%lx\n",
+		       setup_elfcorehdr, setup_elfcorehdr_size);
+		reserve_bootmem(setup_elfcorehdr, setup_elfcorehdr_size,
+				BOOTMEM_DEFAULT);
+	}
+#endif
 #ifdef CONFIG_KEXEC
 	if (crashk_res.start != crashk_res.end)
 		reserve_bootmem(crashk_res.start,