Message-ID: <20150511074728.GA15884@dhcp-128-124.nay.redhat.com>
Date:	Mon, 11 May 2015 15:47:28 +0800
From:	Dave Young <dyoung@...hat.com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, hbabus@...ibm.com,
	linaro-kernel@...ts.linaro.org, geoff@...radead.org,
	catalin.marinas@....com, panand@...hat.com, will.deacon@....com,
	linux-kernel@...r.kernel.org, broonie@...nel.org,
	david.griego@...aro.org, kexec@...ts.infradead.org,
	vgoyal@...hat.com
Subject: Re: [v2 4/5] arm64: add kdump support

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@...aro.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

> 
> > +
> > +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@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> > 
> > 
> 
> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
> 
> 
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