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

[AKASHI Takahiro]

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@xxxxxxxxxx>
> > > ---
> > >   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
> > >
> > >
> > > _______________________________________________
> > > kexec mailing list
> > > kexec@xxxxxxxxxxxxxxxxxxx
> > > http://lists.infradead.org/mailman/listinfo/kexec
> >
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> > kexec@xxxxxxxxxxxxxxxxxxx
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