Re: [PATCH v2 3/6] crash: let arch decide crash memory export to iomem_resource

Sourabh Jain
2025-01-23T11:51:04Z

Hello Hari,

On 23/01/25 15:56, Hari Bathini wrote:
> 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..
>

Hmm. Even I thought of removing that patch for the same reason.
But I noticed the below comment:

/*
* System memory should not be in /proc/iomem but various tools expect it
* (eg kdump).
*/

Since they said eg kdump. I thought maybe it is needed for tools other
then kdump.
But I think this was only added for kdump. And as we know this is not
used in kexec/kdump tool anymore.

I will revert `c40dd2f766440 ("powerpc: Add System RAM to /proc/iomem"). `
change in the next series and take feedback from the community.

Thanks for the review.

- Sourabh Jain

>
>>
>> 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@linux-foundation.org>
>> Cc: Baoquan he <bhe@redhat.com>
>> Cc: Hari Bathini <hbathini@linux.ibm.com>
>> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
>> Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: kexec@lists.infradead.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Sourabh Jain <sourabhjain@linux.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);
>