[PATCH ] kernel/crash_core.c - Add crashkernel=auto for x86 and Arm

[John Donnelly <john.p.donnelly@oracle.com>]

This adds crashkernel=auto feature to configure reserved memory for
vmcore creation to both x86 and Arm platform as implemenented in
RH 4.18.0-147.el8 kernels. The values have been adjusted for x86 and
Arm based from 5.4.0 kernel crash testing.

Signed-off-by: John Donnelly <john.p.donnelly@oracle.com>
Tested-by: John Donnelly <john.p.donnelly@oracle.com>
---
 Documentation/admin-guide/kdump/kdump.rst | 12 ++++++++++
 kernel/crash_core.c                       | 28 +++++++++++++++++++++--
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index ac7e131d2935..7635bbb4ab34 100644
--- a/Documentation/admin-guide/kdump/kdump.rst
+++ b/Documentation/admin-guide/kdump/kdump.rst
@@ -285,6 +285,18 @@ This would mean:
     2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
     3) if the RAM size is larger than 2G, then reserve 128M
 
+Or you can use crashkernel=auto if you have enough memory.  The threshold
+is 1G on x86_64, 2G on arm64, ppc64 and ppc64le. The threshold is 4G for s390x.
+If your system memory is less than the threshold crashkernel=auto will not
+reserve memory.
+
+The automatically reserved memory size varies based on architecture.
+The size changes according to system memory size like below:
+    x86_64: 1G-64G:160M,64G-1T:280M,1T-:512M
+    s390x:  4G-64G:160M,64G-1T:256M,1T-:512M
+    arm64:  2G-:768M
+    ppc64:  2G-4G:384M,4G-16G:512M,16G-64G:1G,64G-128G:2G,128G-:4G
+
 
 
 Boot into System Kernel
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 9f1557b98468..564aca60e57f 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/kexec.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;
 			break;
 		}
@@ -248,6 +258,20 @@ static int __init __parse_crashkernel(char *cmdline,
 	if (suffix)
 		return parse_crashkernel_suffix(ck_cmdline, crash_size,
 				suffix);
+
+	if (strncmp(ck_cmdline, "auto", 4) == 0) {
+#ifdef CONFIG_X86_64
+		ck_cmdline = "1G-64G:160M,64G-1T:280M,1T-:512M";
+#elif defined(CONFIG_S390)
+		ck_cmdline = "4G-64G:160M,64G-1T:256M,1T-:512M";
+#elif defined(CONFIG_ARM64)
+		ck_cmdline = "2G-:768M";
+#elif defined(CONFIG_PPC64)
+		ck_cmdline = "2G-4G:384M,4G-16G:512M,16G-64G:1G,64G-128G:2G,128G-:4G";
+#endif
+		pr_info("Using crashkernel=auto, the size chosen is a best effort estimation.\n");
+	}
+
 	/*
 	 * if the commandline contains a ':', then that's the extended
 	 * syntax -- if not, it must be the classic syntax
-- 
2.20.1