[PATCH 13/15] arm64: kdump: update a kernel doc

Geoff Levand geoff at infradead.org
Fri Nov 6 11:14:37 PST 2015

From: AKASHI Takahiro <takahiro.akashi at linaro.org>

This patch adds arch specific descriptions about kdump usage on arm64
to kdump.txt.

Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
 Documentation/kdump/kdump.txt | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index bc4bd5a..7d3fad0 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,
-s390x and arm architectures.
+s390x, arm and arm64 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
@@ -249,6 +249,29 @@ Dump-capture kernel config options (Arch Dependent, arm)
+Dump-capture kernel config options (Arch Dependent, arm64)
+1) Disable symmetric multi-processing support under "Processor type and
+   features":
+   (If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line
+   when loading the dump-capture kernel, see section "Load the Dump-capture
+   Kernel".)
+2) The maximum memory size on the dump-capture kernel must be limited by
+   specifying:
+   mem=X[MG]
+   where X should be less than or equal to the size in "crashkernel="
+   boot parameter. Kexec-tools will automatically add this.
+3) Currently, kvm will not be enabled on the dump-capture kernel even
+   if it is configured.
 Extended crashkernel syntax
@@ -312,6 +335,8 @@ Boot into System Kernel
    any space below the alignment point may be overwritten by the dump-capture kernel,
    which means it is possible that the vmcore is not that precise as expected.
+   On arm64, use "crashkernel=Y[@X]".  Note that the start address of
+   the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
 Load the Dump-capture Kernel
@@ -334,6 +359,8 @@ For s390x:
 	- Use image or bzImage
 For arm:
 	- Use zImage
+For arm64:
+	- Use vmlinux
 If you are using a uncompressed vmlinux image then use following command
 to load dump-capture kernel.
@@ -377,6 +404,9 @@ For s390x:
 For arm:
 	"1 maxcpus=1 reset_devices"
+For arm64:
+	"1 mem=X[MG] maxcpus=1 reset_devices"
 Notes on loading the dump-capture kernel:
 * By default, the ELF headers are stored in ELF64 format to support

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