[PATCH v26 6/7] arm64: kdump: update a kernel doc

On Fri, Sep 16, 2016 at 05:08:28PM +0100, James Morse wrote:

Hi Akashi,

On 07/09/16 05:29, AKASHI Takahiro wrote:

quoted

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

quoted

diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt

quoted

@@ -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
+  cannot be reset to EL2 on panic.

Nit:
cannot be -> will not be

OK.

We could try to do this, but its more code that could prevent us reaching the
kdump kernel, so we choose not to.

quoted

@@ -370,6 +381,9 @@ For s390x:
 For arm:
 	"1 maxcpus=1 reset_devices"
 
+For arm64:
+	"1 maxcpus=1 reset_devices"
+

'maxcpus=1' is a bit fragile. Since 44dbcc93ab67145 ("arm64: Fix behavior of
maxcpus=N") udev on ubuntu vivid (running on Juno) has taken it upon itself to
bring the secondary cores online, even when booted with 'maxcpus=1'.

Can we change the recomendation to "1 nosmp reset_devices"?

Well, I have no strong opinion here, but I'm not quite sure whether
this change does make any difference in practice.
Looking at kernel/smp.c, the only difference is setup_max_cpus. But
given that arch_disable_smp_support() is null and smp_cpus_done()
ignores "max_cpus" on arm64, I don't think that the change is very
meaningful.

I might miss something.

Thanks,
-Takahiro AKASHI

Thanks,

James