On 11/18/25 at 12:40pm, 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 > > 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://lore.kernel.org/all/[email protected]/ > [1] > > Cc: Aditya Gupta <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: Baoquan he <[email protected]> > Cc: Dave Young <[email protected]> > Cc: Hari Bathini <[email protected]> > Cc: Jiri Bohac <[email protected]> > Cc: Madhavan Srinivasan <[email protected]> > Cc: Mahesh J Salgaonkar <[email protected]> > Cc: Pingfan Liu <[email protected]> > Cc: Ritesh Harjani (IBM) <[email protected]> > Cc: Shivang Upadhyay <[email protected]> > Cc: Vivek Goyal <[email protected]> > Cc: [email protected] > Cc: [email protected] > Signed-off-by: Sourabh Jain <[email protected]> > --- > > Changelog: > > v4 -> v5: > > https://lore.kernel.org/all/[email protected]/ > - Splitted patch from the above patch series. > - Code to create kexec node under /sys/kernel is added, eariler it was > done in [02/05] of the above patch series. > > v5 -> v6: > - Add Crash CMA Range sysfs interface under /sys/kernel > > Note: > This patch is dependent on the below patch: > https://lore.kernel.org/all/[email protected]/ > > --- > .../ABI/testing/sysfs-kernel-kexec-kdump | 10 +++++++++ > kernel/ksysfs.c | 21 +++++++++++++++++++ > 2 files changed, 31 insertions(+)
Acked-by: Baoquan He <[email protected]> > > 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: [email protected] > +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..0ff2179bc603 100644 > --- 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 > -- > 2.51.1 >
