Documentation: kdump: describe arm64 port

Add arch specific descriptions about kdump usage on arm64 to kdump.txt.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Baoquan He <bhe@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: AKASHI Takahiro

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 +249,13 @@ Dump-capture kernel config options (Arch Dependent, arm)
 
     AUTO_ZRELADDR=y
 
+Dump-capture kernel config options (Arch Dependent, arm64)
+----------------------------------------------------------
+
+- Please note that kvm of the dump-capture kernel will not be enabled
+  on non-VHE systems even if it is configured. This is because the CPU
+  will not be reset to EL2 on panic.
+
 Extended crashkernel syntax
 ===========================
 
@@ -312,6 +319,8 @@ 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 +343,8 @@ For s390x:
 	- Use image or bzImage
 For arm:
 	- Use zImage
+For arm64:
+	- Use vmlinux or Image
 
 If you are using a uncompressed vmlinux image then use following command
 to load dump-capture kernel.
@@ -377,6 +388,9 @@ For s390x:
 For arm:
 	"1 maxcpus=1 reset_devices"
 
+For arm64:
+	"1 maxcpus=1 reset_devices"
+
 Notes on loading the dump-capture kernel:
 
 * By default, the ELF headers are stored in ELF64 format to support