linux-kernel - [PATCH 2/2] crash: export crashkernel CMA reservation to userspace

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Message-ID: <20251103035859.1267318-3-sourabhjain@linux.ibm.com>
Date: Mon,  3 Nov 2025 09:28:59 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>, Baoquan he <bhe@...hat.com>,
        Jiri Bohac <jbohac@...e.cz>, Shivang Upadhyay <shivangu@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, kexec@...ts.infradead.org
Subject: [PATCH 2/2] 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

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Baoquan he <bhe@...hat.com>
Cc: Jiri Bohac <jbohac@...e.cz>
Cc: Shivang Upadhyay <shivangu@...ux.ibm.com>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: kexec@...ts.infradead.org
Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
---
 .../ABI/testing/sysfs-kernel-kexec-kdump        | 10 ++++++++++
 kernel/ksysfs.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 96b24565b68e..f6089e38de5f 100644
--- a/Documentation/ABI/testing/sysfs-kernel-kexec-kdump
+++ b/Documentation/ABI/testing/sysfs-kernel-kexec-kdump
@@ -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@...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
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index eefb67d9883c..3855937aa923 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -135,6 +135,22 @@ static ssize_t kexec_crash_loaded_show(struct kobject *kobj,
 }
 KERNEL_ATTR_RO(kexec_crash_loaded);
 
+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);
+
 static ssize_t kexec_crash_size_show(struct kobject *kobj,
 				       struct kobj_attribute *attr, char *buf)
 {
@@ -260,6 +276,7 @@ static struct attribute * kernel_attrs[] = {
 #ifdef CONFIG_CRASH_DUMP
 	&kexec_crash_loaded_attr.attr,
 	&kexec_crash_size_attr.attr,
+	&kexec_crash_cma_ranges_attr.attr,
 #endif
 #endif
 #ifdef CONFIG_VMCORE_INFO
-- 
2.51.0