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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Dave Young <>
Date: Mon, 4 Jun 2018 01:38:25 -0400
Subject: [PATCH] kdump: round up the total memory size to 128M for crashkernel

Message-id: <>
Patchwork-id: 8165
O-Subject: [kernel team] [PATCH RHEL8.0 V2 1/2] kdump: round up the total memory size to 128M for crashkernel reservation
Bugzilla: 1507353
RH-Acked-by: Don Zickus <>
RH-Acked-by: Baoquan He <>
RH-Acked-by: Pingfan Liu <>

Tested: ppc64le, x86_64 with several memory sizes.

The total memory size we get in kernel is usually slightly less than 2G with
2G memory module machine. The main reason is bios/firmware reserve some area
it will not export all memory as usable to Linux.

2G memory X86 kvm guest test result of the total_mem value:
UEFI boot with ovmf: 0x7ef10000
Legacy boot kvm guest: 0x7ff7cc00
This is also a problem on arm64 UEFI booted system according to my test.

Thus for example crashkernel=1G-2G:128M,  if we have a 1G memory
machine, we get total size 1023M from firmware then it will not fall
into 1G-2G thus no memory reserved.  User will never know that, it is
hard to let user to know the exact total value we get in kernel

An option is to use dmi/smbios to get physical memory size, but it's not
reliable as well. According to Prarit hardware vendors sometimes screw this up.
Thus round up total size to 128M to workaround this problem.

Posted below patch in upstream, but no response yet:

Upstream Status: RHEL only
Signed-off-by: Dave Young <>
Signed-off-by: Herton R. Krzesinski <>
 kernel/crash_core.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 18175687133a..e4dfe2a05a31 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -7,6 +7,7 @@
 #include <linux/crash_core.h>
 #include <linux/utsname.h>
 #include <linux/vmalloc.h>
+#include <linux/sizes.h>

 #include <asm/page.h>
 #include <asm/sections.h>
@@ -39,6 +40,15 @@ static int __init parse_crashkernel_mem(char *cmdline,
 					unsigned long long *crash_base)
 	char *cur = cmdline, *tmp;
+	unsigned long long total_mem = system_ram;
+	/*
+	 * Firmware sometimes reserves some memory regions for it's own use.
+	 * so we get less than actual system memory size.
+	 * Workaround this by round up the total size to 128M which is
+	 * enough for most test cases.
+	 */
+	total_mem = roundup(total_mem, SZ_128M);

 	/* for each entry of the comma-separated list */
 	do {
@@ -83,13 +93,13 @@ static int __init parse_crashkernel_mem(char *cmdline,
 			return -EINVAL;
 		cur = tmp;
-		if (size >= system_ram) {
+		if (size >= total_mem) {
 			pr_warn("crashkernel: invalid size\n");
 			return -EINVAL;

 		/* match ? */
-		if (system_ram >= start && system_ram < end) {
+		if (total_mem >= start && total_mem < end) {
 			*crash_size = size;