linux-kernel - Re: [PATCH v6] crash: export crashkernel CMA reservation to userspace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <aR7mYAIBI1zYJ3rg@MiWiFi-R3L-srv>
Date: Thu, 20 Nov 2025 17:58:56 +0800
From: Baoquan he <bhe@...hat.com>
To: Sourabh Jain <sourabhjain@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, Aditya Gupta <adityag@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <dyoung@...hat.com>,
	Hari Bathini <hbathini@...ux.ibm.com>, Jiri Bohac <jbohac@...e.cz>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
	Pingfan Liu <piliu@...hat.com>,
	"Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
	Shivang Upadhyay <shivangu@...ux.ibm.com>,
	Vivek Goyal <vgoyal@...hat.com>, linuxppc-dev@...ts.ozlabs.org,
	kexec@...ts.infradead.org
Subject: Re: [PATCH v6] crash: export crashkernel CMA reservation to userspace

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/20251016142831.144515-1-sourabhjain@linux.ibm.com/ [1]
> 
> Cc: Aditya Gupta <adityag@...ux.ibm.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Baoquan he <bhe@...hat.com>
> Cc: Dave Young <dyoung@...hat.com>
> Cc: Hari Bathini <hbathini@...ux.ibm.com>
> Cc: Jiri Bohac <jbohac@...e.cz>
> Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
> Cc: Mahesh J Salgaonkar <mahesh@...ux.ibm.com>
> Cc: Pingfan Liu <piliu@...hat.com>
> Cc: Ritesh Harjani (IBM) <ritesh.list@...il.com>
> Cc: Shivang Upadhyay <shivangu@...ux.ibm.com>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: kexec@...ts.infradead.org
> Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
> ---
> 
> Changelog:
> 
> v4 -> v5:
>  https://lore.kernel.org/all/20251114152550.ac2dd5e23542f09c62defec7@linux-foundation.org/
>  - 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/20251117035153.1199665-1-sourabhjain@linux.ibm.com/
> 
> ---
>  .../ABI/testing/sysfs-kernel-kexec-kdump      | 10 +++++++++
>  kernel/ksysfs.c                               | 21 +++++++++++++++++++
>  2 files changed, 31 insertions(+)

Acked-by: Baoquan He <bhe@...hat.com>

> 
> 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..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
>