linux-kernel - Re: [PATCH RESEND v1 2/5] crash: let arch decide crash memory export to iomem

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Message-ID: <Z35gnO2N/LFt1E7E@MiWiFi-R3L-srv>
Date: Wed, 8 Jan 2025 19:25:16 +0800
From: Baoquan he <bhe@...hat.com>
To: Sourabh Jain <sourabhjain@...ux.ibm.com>
Cc: linuxppc-dev@...ts.ozlabs.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hari Bathini <hbathini@...ux.ibm.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v1 2/5] crash: let arch decide crash memory export
 to iomem_resource

Hi,

On 01/08/25 at 03:44pm, Sourabh Jain wrote:
> insert_crashkernel_resources() adds crash memory to iomem_resource if
> generic crashkernel reservation is enabled on an architecture.
> 
> On PowerPC, system RAM is added to iomem_resource. See commit
> c40dd2f766440 ("powerpc: Add System RAM to /proc/iomem").
> 
> Enabling generic crashkernel reservation on PowerPC leads to a conflict
> when system RAM is added to iomem_resource because a part of the system
> RAM, the crashkernel memory, has already been added to iomem_resource.
> 
> The next commit in the series "powerpc/crash: use generic crashkernel
> reservation" enables generic crashkernel reservation on PowerPC. If the
> crashkernel is added to iomem_resource, the kernel fails to add
> system RAM to /proc/iomem and prints the following traces:
> 
> CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.13.0-rc2+
> snip...
> NIP [c000000002016b3c] add_system_ram_resources+0xf0/0x15c
> LR [c000000002016b34] add_system_ram_resources+0xe8/0x15c
> Call Trace:
> [c00000000484bbc0] [c000000002016b34] add_system_ram_resources+0xe8/0x15c
> [c00000000484bc20] [c000000000010a4c] do_one_initcall+0x7c/0x39c
> [c00000000484bd00] [c000000002005418] do_initcalls+0x144/0x18c
> [c00000000484bd90] [c000000002005714] kernel_init_freeable+0x21c/0x290
> [c00000000484bdf0] [c0000000000110f4] kernel_init+0x2c/0x1b8
> [c00000000484be50] [c00000000000dd3c] ret_from_kernel_user_thread+0x14/0x1c
> 
> To avoid this, an architecture hook is added in
> insert_crashkernel_resources(), allowing the architecture to decide
> whether crashkernel memory should be added to iomem_resource.

Have you tried defining HAVE_ARCH_ADD_CRASH_RES_TO_IOMEM_EARLY in ppc to
add crashkernel region to iomem early? Now there are two branches in the
existing code, adding a hook will make three ways.