Commit aa014556 authored by Sourabh Jain's avatar Sourabh Jain Committed by Andrew Morton
Browse files

crash: export crashkernel CMA reservation to userspace 

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

The reason for not including Crash CMA Ranges in /proc/iomem is to avoid
conflicts.  It has been observed that contiguous memory ranges are
sometimes shown as two separate System RAM entries in /proc/iomem.  If a
CMA range overlaps two System RAM ranges, adding crashk_res to /proc/iomem
can create a conflict.  Reference [1] describes one such instance on the
PowerPC architecture.

Link: https://lkml.kernel.org/r/20251118071023.1673329-1-sourabhjain@linux.ibm.com
Link: https://lore.kernel.org/all/20251016142831.144515-1-sourabhjain@linux.ibm.com/

 [1]
Signed-off-by: default avatarSourabh Jain <sourabhjain@linux.ibm.com>
Acked-by: default avatarBaoquan He <bhe@redhat.com>
Cc: Aditya Gupta <adityag@linux.ibm.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>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent fdd76c8d

Documentation/ABI/testing/sysfs-kernel-kexec-kdump

+10 −0
Original line number Diff line number Diff line
@@ -41,3 +41,13 @@ 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

kernel/ksysfs.c

+21 −0
Original line number Diff line number Diff line
@@ -135,6 +135,24 @@ static ssize_t kexec_crash_loaded_show(struct kobject *kobj, 
}

KERNEL_ATTR_RO(kexec_crash_loaded);



#ifdef CONFIG_CRASH_RESERVE

static ssize_t kexec_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;

}

KERNEL_ATTR_RO(kexec_crash_cma_ranges);

#endif /* CONFIG_CRASH_RESERVE */



static ssize_t kexec_crash_size_show(struct kobject *kobj,

				       struct kobj_attribute *attr, char *buf)

{
@@ -260,6 +278,9 @@ static struct attribute * kernel_attrs[] = { 
#ifdef CONFIG_CRASH_DUMP

	&kexec_crash_loaded_attr.attr,

	&kexec_crash_size_attr.attr,

#ifdef CONFIG_CRASH_RESERVE

	&kexec_crash_cma_ranges_attr.attr,

#endif

#endif

#endif

#ifdef CONFIG_VMCORE_INFO