linux-kernel - Re: [PATCH v2 3/6] crash: let arch decide crash memory export to iomem

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Message-ID: <9207962e-acfe-4d68-a050-370ab0a48efa@linux.ibm.com>
Date: Thu, 23 Jan 2025 15:56:45 +0530
From: Hari Bathini <hbathini@...ux.ibm.com>
To: Sourabh Jain <sourabhjain@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org
Cc: Andrew Morton <akpm@...ux-foundation.org>, Baoquan he <bhe@...hat.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/6] crash: let arch decide crash memory export to
 iomem_resource

Hi Sourabh,

On 21/01/25 5:24 pm, 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").

The changelog clearly says the patch was added for kdump. But 
kexec-tools or kernel code for kdump on powerpc don't seem to have relied
on that. Device-tree memory nodes were used instead? Wondering if
dropping commit c40dd2f766440 is better..

- Hari

> 
> 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.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Baoquan he <bhe@...hat.com>
> Cc: Hari Bathini <hbathini@...ux.ibm.com>
> Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
> Cc: Mahesh Salgaonkar <mahesh@...ux.ibm.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: kexec@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
> ---
>   include/linux/crash_reserve.h | 11 +++++++++++
>   kernel/crash_reserve.c        |  3 +++
>   2 files changed, 14 insertions(+)
> 
> diff --git a/include/linux/crash_reserve.h b/include/linux/crash_reserve.h
> index 1fe7e7d1b214..f1205d044dae 100644
> --- a/include/linux/crash_reserve.h
> +++ b/include/linux/crash_reserve.h
> @@ -18,6 +18,17 @@ int __init parse_crashkernel(char *cmdline, unsigned long long system_ram,
>   		unsigned long long *crash_size, unsigned long long *crash_base,
>   		unsigned long long *low_size, bool *high);
>   
> +#ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
> +
> +#ifndef arch_add_crash_res_to_iomem
> +static inline bool arch_add_crash_res_to_iomem(void)
> +{
> +	return true;
> +}
> +#endif
> +
> +#endif
> +
>   #ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
>   #ifndef DEFAULT_CRASH_KERNEL_LOW_SIZE
>   #define DEFAULT_CRASH_KERNEL_LOW_SIZE	(128UL << 20)
> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
> index aff7c0fdbefa..190104f32fe1 100644
> --- a/kernel/crash_reserve.c
> +++ b/kernel/crash_reserve.c
> @@ -460,6 +460,9 @@ void __init reserve_crashkernel_generic(unsigned long long crash_size,
>   #ifndef HAVE_ARCH_ADD_CRASH_RES_TO_IOMEM_EARLY
>   static __init int insert_crashkernel_resources(void)
>   {
> +	if (!arch_add_crash_res_to_iomem())
> +		return 0;
> +
>   	if (crashk_res.start < crashk_res.end)
>   		insert_resource(&iomem_resource, &crashk_res);
>