[PATCH v2 2/4] mips: kdump: Capture kernel should be able to see old memories

[Youling Tang]

From: Huacai Chen <chenhc at lemote.com>

kexec-tools use mem=X at Y to pass usable memories to capture kernel, but
in commit a94e4f24ec836c8984f83959 ("MIPS: init: Drop boot_mem_map") all
BIOS passed memories are removed by early_parse_mem(). I think this is
reasonable for a normal kernel but not for a capture kernel, because a
capture kernel should be able to see all old memories, even though it is
not supposed to use them.

Fixes: a94e4f24ec836c8984f83959 ("MIPS: init: Drop boot_mem_map")
Signed-off-by: Huacai Chen <chenhuacai at kernel.org>
Signed-off-by: Youling Tang <tangyouling at loongson.cn>
---
v2:
- Determine whether it is a capture kernel by judging whether there
  is an "elfcorehdr" parameter in the cmdline.

 arch/mips/kernel/setup.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index 9338520..1bc8a9cc 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -352,8 +352,13 @@ static int __init early_parse_mem(char *p)
 	 */
 	if (usermem == 0) {
 		usermem = 1;
-		memblock_remove(memblock_start_of_DRAM(),
-			memblock_end_of_DRAM() - memblock_start_of_DRAM());
+		/*
+		 * During the kdump operation, the old memory should be
+		 * visible to the capture kernel.
+		 */
+		if (!strstr(boot_command_line, "elfcorehdr"))
+			memblock_remove(memblock_start_of_DRAM(),
+				memblock_end_of_DRAM() - memblock_start_of_DRAM());
 	}
 	start = 0;
 	size = memparse(p, &p);
-- 
2.1.0