[v2,1/2] powerpc/fadump: reserve memory at an offset closer to bottom of RAM

Submitted by Hari Bathini on March 16, 2017, 9:05 p.m.

Details

Message ID 148969794004.4130.14805754334064000704.stgit@hbathini.in.ibm.com
State Accepted
Headers show

Commit Message

Hari Bathini March 16, 2017, 9:05 p.m.
Currently, the area to preserve boot memory is reserved at the top of
RAM. This leaves fadump vulnerable to memory hot-remove operations. As
memory for fadump has to be reserved early in the boot process, fadump
can't be registered after a memory hot-remove operation. Though this
problem can't be eleminated completely, the impact can be minimized by
reserving memory at an offset closer to bottom of the RAM. The offset
for fadump memory reservation can be any value greater than fadump boot
memory size.

Signed-off-by: Hari Bathini <hbathini@linux.vnet.ibm.com>
---

Changes from v1:
* Finding the offset based on memory holes/availability
* Improved error checking


 arch/powerpc/kernel/fadump.c |   33 ++++++++++++++++++++++++++-------
 1 file changed, 26 insertions(+), 7 deletions(-)

Comments

Michael Ellerman April 3, 2017, 10:13 a.m.
On Thu, 2017-03-16 at 21:05:26 UTC, Hari Bathini wrote:
> Currently, the area to preserve boot memory is reserved at the top of
> RAM. This leaves fadump vulnerable to memory hot-remove operations. As
> memory for fadump has to be reserved early in the boot process, fadump
> can't be registered after a memory hot-remove operation. Though this
> problem can't be eleminated completely, the impact can be minimized by
> reserving memory at an offset closer to bottom of the RAM. The offset
> for fadump memory reservation can be any value greater than fadump boot
> memory size.
> 
> Signed-off-by: Hari Bathini <hbathini@linux.vnet.ibm.com>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/f6e6bedb773118713a8eb3736a4c99

cheers

Patch hide | download patch | download mbox

diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
index 8ff0dd4..33b2da3 100644
--- a/arch/powerpc/kernel/fadump.c
+++ b/arch/powerpc/kernel/fadump.c
@@ -319,15 +319,34 @@  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. */
 		size = get_fadump_area_size();
-		base = memory_boundary - size;
-		memblock_reserve(base, size);
-		printk(KERN_INFO "Reserved %ldMB of memory at %ldMB "
-				"for firmware-assisted dump\n",
-				(unsigned long)(size >> 20),
-				(unsigned long)(base >> 20));
+
+		/*
+		 * Reserve memory at an offset closer to bottom of the RAM to
+		 * minimize the impact of memory hot-remove operation. We can't
+		 * use memblock_find_in_range() here since it doesn't allocate
+		 * from bottom to top.
+		 */
+		for (base = fw_dump.boot_memory_size;
+		     base <= (memory_boundary - size);
+		     base += size) {
+			if (memblock_is_region_memory(base, size) &&
+			    !memblock_is_region_reserved(base, size))
+				break;
+		}
+		if ((base > (memory_boundary - size)) ||
+		    memblock_reserve(base, size)) {
+			pr_err("Failed to reserve memory\n");
+			return 0;
+		}
+
+		pr_info("Reserved %ldMB of memory at %ldMB for firmware-"
+			"assisted dump (System RAM: %ldMB)\n",
+			(unsigned long)(size >> 20),
+			(unsigned long)(base >> 20),
+			(unsigned long)(memblock_phys_mem_size() >> 20));
 	}
+
 	fw_dump.reserve_dump_area_start = base;
 	fw_dump.reserve_dump_area_size = size;
 	return 1;