linux-kernel - Re: [PATCH linux-next v3 05/14] crash: clean up kdump related config items

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Message-ID: <c5e9996e4d2ba2a0849d65f68e3dce94fffc5828.camel@physik.fu-berlin.de>
Date: Thu, 22 Aug 2024 11:37:09 +0200
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: Baoquan He <bhe@...hat.com>
Cc: linux-kernel@...r.kernel.org, Dave Vasilevsky <dave@...ilevsky.ca>, 
 Michael Ellerman <mpe@...erman.id.au>, kexec@...ts.infradead.org,
 debian-powerpc@...ts.debian.org, x86@...nel.org, 
 linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org, 
 linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
 linux-mips@...r.kernel.org,  linux-riscv@...ts.infradead.org,
 loongarch@...ts.linux.dev,  akpm@...ux-foundation.org,
 ebiederm@...ssion.com, hbathini@...ux.ibm.com,  piliu@...hat.com,
 viro@...iv.linux.org.uk, Sam James <sam@...too.org>
Subject: Re: [PATCH linux-next v3 05/14] crash: clean up kdump related
 config items

Hi Baoquan,

On Thu, 2024-08-22 at 17:17 +0800, Baoquan He wrote:
> > The change to enable CONFIG_CRASH_DUMP by default apparently broke the boot
> > on 32-bit Power Macintosh systems which fail after GRUB with:
> > 
> > 	"Error: You can't boot a kdump kernel from OF!"
> > 
> > We may have to turn this off for 32-bit Power Macintosh systems.
> > 
> > See this thread on debian-powerpc ML: https://lists.debian.org/debian-powerpc/2024/07/msg00001.html
> 
> If so, fix need be made.
> 
> We may need change in ARCH_SUPPORTS_CRASH_DUMP of ppc, can you or anyone
> post a patch? I don't know how to identify 32-bit Power Macintosh.
> 
> arch/powerpc/Kconfig:
> ===
> config ARCH_SUPPORTS_CRASH_DUMP
>         def_bool PPC64 || PPC_BOOK3S_32 || PPC_85xx || (44x && !SMP)
>         
> config ARCH_SELECTS_CRASH_DUMP
>         def_bool y
>         depends on CRASH_DUMP
>         select RELOCATABLE if PPC64 || 44x || PPC_85xx
> ......
> config PHYSICAL_START
>         hex "Physical address where the kernel is loaded" if PHYSICAL_START_BOOL
>         default "0x02000000" if PPC_BOOK3S && CRASH_DUMP && !NONSTATIC_KERNEL
>         default "0x00000000"

I think the architecture does support crash dumps, but I think the kernel has to
be booted from kexec in this case. Booting a kernel with CRASH_DUMP enabled won't
work from Open Firmware. So, I think CRASH_DUMP should just be disabled for
PPC_BOOK3S_32 by default and users who want to use it on these systems, will have to
enable it explicitly.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913