linux-kernel - Re: [PATCH v2 5/5] crash: export crashkernel CMA reservation to userspace

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Message-ID: <f2c83fff-a5cd-4894-8014-f6b289e89019@linux.ibm.com>
Date: Fri, 7 Nov 2025 12:45:55 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: Aditya Gupta <adityag@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>, 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 v2 5/5] crash: export crashkernel CMA reservation to
 userspace



On 06/11/25 10:21, Sourabh Jain 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
>
> Cc: Aditya Gupta <adityag@...ux.ibm.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Baoquan he <bhe@...hat.com>
> Cc: Dave Young <dyoung@...hat.com>
> Cc: Hari Bathini <hbathini@...ux.ibm.com>
> Cc: Jiri Bohac <jbohac@...e.cz>
> Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
> Cc: Mahesh J Salgaonkar <mahesh@...ux.ibm.com>
> Cc: Pingfan Liu <piliu@...hat.com>
> Cc: Ritesh Harjani (IBM) <ritesh.list@...il.com>
> Cc: Shivang Upadhyay <shivangu@...ux.ibm.com>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: kexec@...ts.infradead.org
> Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
> ---
>   Documentation/ABI/testing/sysfs-kernel-kexec-kdump | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-kernel-kexec-kdump b/Documentation/ABI/testing/sysfs-kernel-kexec-kdump
> index 00c00f380fea..f59051b5d96d 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-kexec-kdump
> +++ b/Documentation/ABI/testing/sysfs-kernel-kexec-kdump
> @@ -49,3 +49,13 @@ Description:	read only
>   		is used by the user space utility kexec to support updating the
>   		in-kernel kdump image during hotplug operations.
>   User:		Kexec tools
> +
> +What:		/sys/kernel/kexec/crash_cma_ranges
> +Date:		Nov 2025
> +Contact:	kexec@...ts.infradead.org
> +Description:	read only
> +		Provides information about the memory ranges reserved from
> +		the Contiguous Memory Allocator (CMA) area that are allocated
> +		to the crash (kdump) kernel. It lists the start and end physical
> +		addresses of CMA regions assigned for crashkernel use.
> +User:		kdump service
While rebasing the v1 patches, the hunk that adds the show function 
didn't get picked up.
I will send v3 with a show function to export the crashkernel CMA 
reservation.

- Sourabh Jain