diff mbox

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

Message ID 20160907042908.6232-7-takahiro.akashi@linaro.org (mailing list archive)
State New, archived
Headers show

Commit Message

AKASHI Takahiro Sept. 7, 2016, 4:29 a.m. UTC 
This patch adds 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>
---
 Documentation/kdump/kdump.txt | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

Comments

James Morse Sept. 16, 2016, 4:08 p.m. UTC | #1 
Hi Akashi,

On 07/09/16 05:29, AKASHI Takahiro wrote:
> This patch adds arch specific descriptions about kdump usage on arm64
> to kdump.txt.

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

> @@ -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

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


> @@ -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"?


Thanks,

James
AKASHI Takahiro Sept. 20, 2016, 8:27 a.m. UTC | #2 
On Fri, Sep 16, 2016 at 05:08:28PM +0100, James Morse wrote:
> Hi Akashi,
> 
> On 07/09/16 05:29, AKASHI Takahiro wrote:
> > This patch adds arch specific descriptions about kdump usage on arm64
> > to kdump.txt.
> 
> > diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> 
> > @@ -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.
> 
> 
> > @@ -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
>
Matthias Brugger Sept. 26, 2016, 5:21 p.m. UTC | #3 
On 16/09/16 18:08, James Morse wrote:
> Hi Akashi,
>
> On 07/09/16 05:29, AKASHI Takahiro wrote:
>> This patch adds arch specific descriptions about kdump usage on arm64
>> to kdump.txt.
>
>> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
>
>> @@ -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
>
> We could try to do this, but its more code that could prevent us reaching the
> kdump kernel, so we choose not to.
>
>
>> @@ -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'.
>

This looks pretty much like a bug to me and should get fixed on their site.

> Can we change the recomendation to "1 nosmp reset_devices"?
>
>
> Thanks,
>
> James
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
diff mbox

Patch

diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index 88ff63d..c090531 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 +249,13 @@  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.
+
 Extended crashkernel syntax
 ===========================
 
@@ -305,6 +312,8 @@  Boot into System Kernel
    kernel will automatically locate the crash kernel image within the
    first 512MB of RAM if X is not given.
 
+   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
 ============================
@@ -327,6 +336,8 @@  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.
@@ -370,6 +381,9 @@  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