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

[Dave Young <dyoung@redhat.com>]

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..

> +
> +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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