linux-kernel - Re: [PATCH v5] crash: export crashkernel CMA reservation to userspace

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Message-ID: <469c97cb-5ea1-4c2b-a70f-b1a6febf70df@linux.ibm.com>
Date: Tue, 18 Nov 2025 00:03:54 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, Aditya Gupta <adityag@...ux.ibm.com>,
        Baoquan he <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
        Hari Bathini <hbathini@...ux.ibm.com>, Jiri Bohac <jbohac@...e.cz>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Pingfan Liu <piliu@...hat.com>,
        "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
        Shivang Upadhyay <shivangu@...ux.ibm.com>,
        Vivek Goyal <vgoyal@...hat.com>, linuxppc-dev@...ts.ozlabs.org,
        kexec@...ts.infradead.org
Subject: Re: [PATCH v5] crash: export crashkernel CMA reservation to userspace



On 17/11/25 23:12, Andrew Morton wrote:
> On Mon, 17 Nov 2025 09:49:05 +0530 Sourabh Jain <sourabhjain@...ux.ibm.com> wrote:
>
>> Add a sysfs entry /sys/kernel/kexec/crash_cma_ranges to expose all
>> CMA crashkernel ranges.
>>
>> This allows userspace tools configuring kdump to determine how much
>> memory is reserved for crashkernel. If CMA is used, tools can warn
>> users when attempting to capture user pages with CMA reservation.
>>
>> The new sysfs hold the CMA ranges in below format:
>>
>> cat /sys/kernel/kexec/crash_cma_ranges
>> 100000000-10c7fffff
>>
>> There are already four kexec and kdump sysfs entries under /sys/kernel.
>> Adding more entries there would clutter the directory. To avoid this,
>> the new crash_cma_ranges sysfs entry is placed in a new kexec node under
>> /sys/kernel/.
> I suggest not creating /sys/kernel/kexec in this patch.
>
> Moving everything into a new /sys/kernel/kexec is a separate patchset
> and a separate concept and it might never be merged - it changes ABI!
>
> So let's put crash_cma_ranges in /sys/kernel and move it to
> /sys/kernel/kexec within the other patchset.

Yeah sure. I will send the patches accordingly.

Thanks,
Sourabh Jain