[PATCH 1/2] powerpc/fadump: reserve memory at halfway mark

[Hari Bathini]

Currently, the area to preserve boot memory is reserved at the top of
RAM. This leaves fadump vulnerable to DLPAR memory remove operations.
As memory for fadump needs to be reserved early in the boot process,
fadump can't be registered after a DLPAR memory remove operation.
While this problem can't be eleminated completely, the impact can be
minimized by reserving memory at the halfway mark instead. With this
change, fadump can register successfully after a DLPAR memory remove
operation as long as the sum of the sizes of boot memory and memory
removed is less than half of the total available memory.

Signed-off-by: Hari Bathini <hbathini at linux.vnet.ibm.com>
---
 arch/powerpc/kernel/fadump.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
index 8ff0dd4..9c85c5a 100644
--- a/arch/powerpc/kernel/fadump.c
+++ b/arch/powerpc/kernel/fadump.c
@@ -319,9 +319,13 @@ int __init fadump_reserve_mem(void)
 		pr_debug("fadumphdr_addr = %p\n",
 				(void *) fw_dump.fadumphdr_addr);
 	} else {
-		/* Reserve the memory at the top of memory. */
+		/*
+		 * Reserve memory at the halfway mark to minimize
+		 * the impact of DLPAR memory remove operation.
+		 */
+		base = PAGE_ALIGN(memory_boundary/2);
 		size = get_fadump_area_size();
-		base = memory_boundary - size;
+		WARN_ON((base + size) > memory_boundary);
 		memblock_reserve(base, size);
 		printk(KERN_INFO "Reserved %ldMB of memory at %ldMB "
 				"for firmware-assisted dump\n",