Re: [PATCH v3 5/5] crash: export crashkernel CMA reservation to userspace

[Baoquan he <bhe@redhat.com>]

On 11/10/25 at 10:01am, Sourabh Jain wrote:
> Add a sysfs entry /sys/kernel/kexec/crash_cma_ranges to expose all
> CMA crashkernel ranges.

I am not against this way. While wondering if it's more appropriate to
export them into iomem_resource just like crashk_res and crashk_low_res
doing.

> 
> 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@linux.ibm.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Baoquan he <bhe@redhat.com>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Hari Bathini <hbathini@linux.ibm.com>
> Cc: Jiri Bohac <jbohac@suse.cz>
> Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
> Cc: Mahesh J Salgaonkar <mahesh@linux.ibm.com>
> Cc: Pingfan Liu <piliu@redhat.com>
> Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> Cc: Shivang Upadhyay <shivangu@linux.ibm.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: kexec@lists.infradead.org
> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
> ---
> Changelog:
>  - Add the missing hunk to export crash_cma_ranges sysfs
> 
> ---
>  .../ABI/testing/sysfs-kernel-kexec-kdump        | 10 ++++++++++
>  kernel/kexec_core.c                             | 17 +++++++++++++++++
>  2 files changed, 27 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@lists.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
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 7476a46de5d6..da6ff72b4669 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -1271,6 +1271,22 @@ static ssize_t crash_size_store(struct kobject *kobj,
>  }
>  static struct kobj_attribute crash_size_attr = __ATTR_RW(crash_size);
>  
> +static ssize_t crash_cma_ranges_show(struct kobject *kobj,
> +				     struct kobj_attribute *attr, char *buf)
> +{
> +
> +	ssize_t len = 0;
> +	int i;
> +
> +	for (i = 0; i < crashk_cma_cnt; ++i) {
> +		len += sysfs_emit_at(buf, len, "%08llx-%08llx\n",
> +				     crashk_cma_ranges[i].start,
> +				     crashk_cma_ranges[i].end);
> +	}
> +	return len;
> +}
> +static struct kobj_attribute crash_cma_ranges_attr = __ATTR_RO(crash_cma_ranges);
> +
>  #ifdef CONFIG_CRASH_HOTPLUG
>  static ssize_t crash_elfcorehdr_size_show(struct kobject *kobj,
>  			       struct kobj_attribute *attr, char *buf)
> @@ -1289,6 +1305,7 @@ static struct attribute *kexec_attrs[] = {
>  #ifdef CONFIG_CRASH_DUMP
>  	&crash_loaded_attr.attr,
>  	&crash_size_attr.attr,
> +	&crash_cma_ranges_attr.attr,
>  #ifdef CONFIG_CRASH_HOTPLUG
>  	&crash_elfcorehdr_size_attr.attr,
>  #endif
> -- 
> 2.51.1
>