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/
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Acked-by: Baoquan 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: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/ABI/testing/sysfs-kernel-kexec-kdump b/Documentation/ABI/testing/sysfs-kernel-kexec-kdump
index 96b24565b68e15ee2270f4386e0637d08cab1d5e..f6089e38de5facddc6a2d4c16de17d8f763b6f56 100644 (file)
--- 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@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/ksysfs.c b/kernel/ksysfs.c
index eefb67d9883c2ca876023d75bb752b26a93a839b..0ff2179bc6031b7aabd8a62a48f05f028da8b04f 100644 (file)
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -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