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SubjectRe: [v2 4/5] arm64: add kdump support
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
>
>
> _______________________________________________
> kexec mailing list
> kexec@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
>
>


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