----------------------------------------
Add arm specific parts to kdump kernel documentation.
It seem that we prefer to use nr_cpus=1 instead of maxcpus=1. but nr_cpus
does not work fine on arm.
There will be a warning when dump-caputre kernel booting if use nr_cpus:
"[ 0.000000] DT/cpu 2nodes greater than max cores 1, capping them"
This is from arch/arm/kernel/devtree.c, in function
void __init arm_dt_init_cpu_maps(void)
145 if (WARN(cpuidx > nr_cpu_ids, "DT /cpu %u nodes greater than "
146 "max cores %u, capping them\n",
147 cpuidx, nr_cpu_ids)) {
148 cpuidx = nr_cpu_ids;
149 break;
150 }
Since we have already using nr_cpus to specify the number of cpus we
want to be online, kdump should not to make the comparison with dtb
(which is strongly recommended on arm-32bit ) again, but it does, so the
warning out.
Meanwhile the maxcpus works fine.
v1 -> v2:
- Add description about dump-capture kernel config options(Arch Dependent, arm).
- Add description about the defference between arm and the others.
on extended crashkernel syntax
Signed-off-by: Hu Keping <hukeping at huawei.com>
---
Documentation/kdump/kdump.txt | 37 ++++++++++++++++++++++++++++++++++---
1 file changed, 34 insertions(+), 3 deletions(-)
diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index 88d5a86..d07b902 100644
--- a/Documentation/kdump/kdump.txt
+++ b/Documentation/kdump/kdump.txt
@@ -18,7 +18,7 @@ memory image to a dump file on the local disk, or across the network to
a remote system.
Kdump and kexec are currently supported on the x86, x86_64, ppc64, ia64,
-and s390x architectures.
+s390x and arm architectures.
When the system kernel boots, it reserves a small section of memory for
the dump-capture kernel. This ensures that ongoing Direct Memory Access
@@ -112,7 +112,7 @@ There are two possible methods of using Kdump.
2) Or use the system kernel binary itself as dump-capture kernel and there is
no need to build a separate dump-capture kernel. This is possible
only with the architectures which support a relocatable kernel. As
- of today, i386, x86_64, ppc64 and ia64 architectures support relocatable
+ of today, i386, x86_64, ppc64, ia64 and arm architectures support relocatable
kernel.
Building a relocatable kernel is advantageous from the point of view that
@@ -241,6 +241,14 @@ Dump-capture kernel config options (Arch Dependent, ia64)
kernel will be aligned to 64Mb, so if the start address is not then
any space below the alignment point will be wasted.
+Dump-capture kernel config options (Arch Dependent, arm)
+----------------------------------------------------------
+
+- To use a relocatable kernel,
+ Enable "AUTO_ZRELADDR" support under "Boot" options:
+
+ AUTO_ZRELADDR=y
+
Extended crashkernel syntax
===========================
@@ -256,6 +264,10 @@ The syntax is:
crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
range=start-[end]
+Plesse note, on arm, the offset is required.
+ crashkernel=<range1>:<size1>[,<range2>:<size2>,...]@offset
+ range=start-[end]
+
'start' is inclusive and 'end' is exclusive.
For example:
@@ -296,6 +308,12 @@ Boot into System Kernel
on the memory consumption of the kdump system. In general this is not
dependent on the memory size of the production system.
+ On arm, use "crashkernel=Y at X". Note that the start address of the kernel
+ will be aligned to 128MiB (0x08000000), so if the start address is not then
+ any space blow the alignment point may be overwrited by the dump-caputre kernel,
+ which means it is possible that the vmcore is not that precise as expected.
+
+
Load the Dump-capture Kernel
============================
@@ -315,7 +333,8 @@ For ia64:
- Use vmlinux or vmlinuz.gz
For s390x:
- Use image or bzImage
-
+For arm:
+ - Use zImage
If you are using a uncompressed vmlinux image then use following command
to load dump-capture kernel.
@@ -331,6 +350,15 @@ to load dump-capture kernel.
--initrd=<initrd-for-dump-capture-kernel> \
--append="root=<root-dev> <arch-specific-options>"
+If you are using a compressed zImage, then use following command
+to load dump-capture kernel.
+
+ kexec --type zImage -p <dump-capture-kernel-bzImage> \
+ --initrd=<initrd-for-dump-capture-kernel> \
+ --dtb=<dtb-for-dump-capture-kernel> \
+ --append="root=<root-dev> <arch-specific-options>"
+
+
Please note, that --args-linux does not need to be specified for ia64.
It is planned to make this a no-op on that architecture, but for now
it should be omitted
@@ -347,6 +375,9 @@ For ppc64:
For s390x:
"1 maxcpus=1 cgroup_disable=memory"
+For arm:
+ "1 maxcpus=1 reset_devices"
+
Notes on loading the dump-capture kernel:
* By default, the ELF headers are stored in ELF64 format to support
--
1.8.5.5
