Re: [v2 4/5] arm64: add kdump support

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

Dave,

On 05/11/2015 04:47 PM, Dave Young wrote:
> On 05/08/15 at 08:19pm, Dave Young wrote:
>> Hi,
>>
>> On 04/24/15 at 04:53pm, AKASHI Takahiro wrote:
>>> Please read the following commits for arm64-specific constraints:
>>>      arm64: kdump: reserve memory for crash dump kernel
>>>      arm64: kdump: do not go into EL2 before starting a crash dump kernel
>>>
>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>>> ---
>>>   Documentation/kdump/kdump.txt |   31 ++++++++++++++++++++++++++++++-
>>>   arch/arm64/Kconfig            |   12 ++++++++++++
>>>   2 files changed, 42 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
>>> index bc4bd5a..f9cf6f5 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)
>>>
>>>       AUTO_ZRELADDR=y
>>>
>>> +Dump-capture kernel config options (Arch Dependent, arm64)
>>> +----------------------------------------------------------
>>> +
>>> +1) Disable symmetric multi-processing support under "Processor type and
>>> +   features":
>>> +
>>> +   CONFIG_SMP=n
>>> +
>>> +   (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) Under uefi, 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.
>>
>> I noticed you are passing mem=X in kexec-tools, Pratyush found a problem
>> that vmcore is corrupted because kdump kernel is using the crash notes memory.
>>
>> How does kdump kernel know the system ram range especially the mem_start?
>> Only with the size from mem=? parammeter?
>>
>> In X86 because it use E820 so kexec-tools can pass the memory range to kdump
>> kernel even for UEFI booting. But in arm64 may need find other way to
>> communicate with 2nd kernel like memmap=exactmap in X86..
>
> Discussed with Pratyush in irc, he mentioned that start address is get from
> kernel->entry which was passed by kexec-tools.
>
> So sorry for the noise, it will works fine with the UEFI mem= limitation
> fix from Mark Salter

No, not at all.
As you know, in another thread (with Mark), we're discussing this.
If we conclude that we should go for "memmap=" approach, I will update my patch.

Thanks,
-Takahiro AKASHI


>>
>>> +
>>> +3) Currently, kvm will not be initialized on the dump-capture kernel even
>>> +   if it is configured.
>>> +
>>>   Extended crashkernel syntax
>>>   ===========================
>>>
>>> @@ -312,6 +335,7 @@ 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".
>>>
>>>   Load the Dump-capture Kernel
>>>   ============================
>>> @@ -334,6 +358,8 @@ 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 +403,9 @@ For s390x:
>>>   For arm:
>>>   	"1 maxcpus=1 reset_devices"
>>>
>>> +For arm64:
>>> +	"1 maxcpus=1 mem=X[MG] reset_devices"
>>> +
>>>   Notes on loading the dump-capture kernel:
>>>
>>>   * By default, the ELF headers are stored in ELF64 format to support
>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>> index 5716edf..8e2f545 100644
>>> --- a/arch/arm64/Kconfig
>>> +++ b/arch/arm64/Kconfig
>>> @@ -562,6 +562,18 @@ config KEXEC
>>>   	  but it is independent of the system firmware.   And like a reboot
>>>   	  you can start any kernel with it, not just Linux.
>>>
>>> +config CRASH_DUMP
>>> +	bool "Build kdump crash kernel"
>>> +	help
>>> +	  Generate crash dump after being started by kexec. This should
>>> +	  be normally only set in special crash dump kernels which are
>>> +	  loaded in the main kernel with kexec-tools into a specially
>>> +	  reserved region and then later executed after a crash by
>>> +	  kdump/kexec. The crash dump kernel must be compiled to a
>>> +	  memory address not used by the main kernel.
>>> +
>>> +	  For more details see Documentation/kdump/kdump.txt
>>> +
>>>   config XEN_DOM0
>>>   	def_bool y
>>>   	depends on XEN
>>> --
>>> 1.7.9.5
>>>
>>>
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>>>
>>>
>>
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>>

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