kernel/linux.git/Documentation/admin-guide/kdump, branch v6.18.21

Documentation: Fix admin-guide typos

2025-08-18T16:31:19+00:00

Fix typos. Signed-off-by: Bjorn Helgaas Reviewed-by: Randy Dunlap Signed-off-by: Jonathan Corbet Link: https://lore.kernel.org/r/20250813200526.290420-4-helgaas@kernel.org

Merge tag 'mm-nonmm-stable-2025-08-03-12-47' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2025-08-03T23:23:09+00:00

Pull non-MM updates from Andrew Morton: "Significant patch series in this pull request: - "squashfs: Remove page->mapping references" (Matthew Wilcox) gets us closer to being able to remove page->mapping - "relayfs: misc changes" (Jason Xing) does some maintenance and minor feature addition work in relayfs - "kdump: crashkernel reservation from CMA" (Jiri Bohac) switches us from static preallocation of the kdump crashkernel's working memory over to dynamic allocation. So the difficulty of a-priori estimation of the second kernel's needs is removed and the first kernel obtains extra memory - "generalize panic_print's dump function to be used by other kernel parts" (Feng Tang) implements some consolidation and rationalization of the various ways in which a failing kernel splats information at the operator * tag 'mm-nonmm-stable-2025-08-03-12-47' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (80 commits) tools/getdelays: add backward compatibility for taskstats version kho: add test for kexec handover delaytop: enhance error logging and add PSI feature description samples: Kconfig: fix spelling mistake "instancess" -> "instances" fat: fix too many log in fat_chain_add() scripts/spelling.txt: add notifer||notifier to spelling.txt xen/xenbus: fix typo "notifer" net: mvneta: fix typo "notifer" drm/xe: fix typo "notifer" cxl: mce: fix typo "notifer" KVM: x86: fix typo "notifer" MAINTAINERS: add maintainers for delaytop ucount: use atomic_long_try_cmpxchg() in atomic_long_inc_below() ucount: fix atomic_long_inc_below() argument type kexec: enable CMA based contiguous allocation stackdepot: make max number of pools boot-time configurable lib/xxhash: remove unused functions init/Kconfig: restore CONFIG_BROKEN help text lib/raid6: update recov_rvv.c zero page usage docs: update docs after introducing delaytop ...

kdump, documentation: describe craskernel CMA reservation

2025-07-20T02:08:23+00:00

Describe the new crashkernel ",cma" suffix in Documentation/ Link: https://lkml.kernel.org/r/aEqpQwUy6gqSiUkV@dwarf.suse.cz Signed-off-by: Jiri Bohac Cc: Baoquan He Cc: Dave Young Cc: David Hildenbrand Cc: Donald Dutile Cc: Michal Hocko Cc: Philipp Rudo Cc: Pingfan Liu Cc: Tao Liu Cc: Vivek Goyal Signed-off-by: Andrew Morton

vmcoreinfo: Remove documentation of PG_slab and PG_hugetlb

2025-06-18T11:06:27+00:00

The changes to kernel/vmcore_info.c were sadly not reflected in the documentation. Rectify that for both these flags as well as adding PAGE_UNACCEPTED_MAPCOUNT_VALUE. Signed-off-by: Matthew Wilcox (Oracle) Acked-by: Harry Yoo Link: https://patch.msgid.link/20250611155916.2579160-8-willy@infradead.org Signed-off-by: Vlastimil Babka

x86/crash: pass dm crypt keys to kdump kernel

2025-05-21T17:48:21+00:00

1st kernel will build up the kernel command parameter dmcryptkeys as similar to elfcorehdr to pass the memory address of the stored info of dm crypt key to kdump kernel. Link: https://lkml.kernel.org/r/20250502011246.99238-8-coxu@redhat.com Signed-off-by: Coiby Xu Acked-by: Baoquan He Cc: "Daniel P. Berrange" Cc: Dave Hansen Cc: Dave Young Cc: Jan Pazdziora Cc: Liu Pingfan Cc: Milan Broz Cc: Ondrej Kozina Cc: Vitaly Kuznetsov Signed-off-by: Andrew Morton

crash_dump: reuse saved dm crypt keys for CPU/memory hot-plugging

2025-05-21T17:48:21+00:00

When there are CPU and memory hot un/plugs, the dm crypt keys may need to be reloaded again depending on the solution for crash hotplug support. Currently, there are two solutions. One is to utilizes udev to instruct user space to reload the kdump kernel image and initrd, elfcorehdr and etc again. The other is to only update the elfcorehdr segment introduced in commit 247262756121 ("crash: add generic infrastructure for crash hotplug support"). For the 1st solution, the dm crypt keys need to be reloaded again. The user space can write true to /sys/kernel/config/crash_dm_crypt_key/reuse so the stored keys can be re-used. For the 2nd solution, the dm crypt keys don't need to be reloaded. Currently, only x86 supports the 2nd solution. If the 2nd solution gets extended to all arches, this patch can be dropped. Link: https://lkml.kernel.org/r/20250502011246.99238-5-coxu@redhat.com Signed-off-by: Coiby Xu Acked-by: Baoquan He Cc: "Daniel P. Berrange" Cc: Dave Hansen Cc: Dave Young Cc: Jan Pazdziora Cc: Liu Pingfan Cc: Milan Broz Cc: Ondrej Kozina Cc: Vitaly Kuznetsov Signed-off-by: Andrew Morton

crash_dump: make dm crypt keys persist for the kdump kernel

2025-05-21T17:48:20+00:00

A configfs /sys/kernel/config/crash_dm_crypt_keys is provided for user space to make the dm crypt keys persist for the kdump kernel. Take the case of dumping to a LUKS-encrypted target as an example, here is the life cycle of the kdump copies of LUKS volume keys, 1. After the 1st kernel loads the initramfs during boot, systemd uses an user-input passphrase to de-crypt the LUKS volume keys or simply TPM-sealed volume keys and then save the volume keys to specified keyring (using the --link-vk-to-keyring API) and the keys will expire within specified time. 2. A user space tool (kdump initramfs loader like kdump-utils) create key items inside /sys/kernel/config/crash_dm_crypt_keys to inform the 1st kernel which keys are needed. 3. When the kdump initramfs is loaded by the kexec_file_load syscall, the 1st kernel will iterate created key items, save the keys to kdump reserved memory. 4. When the 1st kernel crashes and the kdump initramfs is booted, the kdump initramfs asks the kdump kernel to create a user key using the key stored in kdump reserved memory by writing yes to /sys/kernel/crash_dm_crypt_keys/restore. Then the LUKS encrypted device is unlocked with libcryptsetup's --volume-key-keyring API. 5. The system gets rebooted to the 1st kernel after dumping vmcore to the LUKS encrypted device is finished Eventually the keys have to stay in the kdump reserved memory for the kdump kernel to unlock encrypted volumes. During this process, some measures like letting the keys expire within specified time are desirable to reduce security risk. This patch assumes, 1) there are 128 LUKS devices at maximum to be unlocked thus MAX_KEY_NUM=128. 2) a key description won't exceed 128 bytes thus KEY_DESC_MAX_LEN=128. And here is a demo on how to interact with /sys/kernel/config/crash_dm_crypt_keys, # Add key #1 mkdir /sys/kernel/config/crash_dm_crypt_keys/7d26b7b4-e342-4d2d-b660-7426b0996720 # Add key #1's description echo cryptsetup:7d26b7b4-e342-4d2d-b660-7426b0996720 > /sys/kernel/config/crash_dm_crypt_keys/description # how many keys do we have now? cat /sys/kernel/config/crash_dm_crypt_keys/count 1 # Add key# 2 in the same way # how many keys do we have now? cat /sys/kernel/config/crash_dm_crypt_keys/count 2 # the tree structure of /crash_dm_crypt_keys configfs tree /sys/kernel/config/crash_dm_crypt_keys/ /sys/kernel/config/crash_dm_crypt_keys/ ├── 7d26b7b4-e342-4d2d-b660-7426b0996720 │ └── description ├── count ├── fce2cd38-4d59-4317-8ce2-1fd24d52c46a │ └── description Link: https://lkml.kernel.org/r/20250502011246.99238-3-coxu@redhat.com Signed-off-by: Coiby Xu Acked-by: Baoquan He Cc: "Daniel P. Berrange" Cc: Dave Hansen Cc: Dave Young Cc: Jan Pazdziora Cc: Liu Pingfan Cc: Milan Broz Cc: Ondrej Kozina Cc: Vitaly Kuznetsov Signed-off-by: Andrew Morton

crash: export PAGE_UNACCEPTED_MAPCOUNT_VALUE to vmcoreinfo

2025-05-12T00:54:04+00:00

On Intel TDX guest, unaccepted memory is unusable free memory which is not managed by buddy, until it's accepted by guest. Before that, it cannot be accessed by the first kernel as well as the kexec'ed kernel. The kexec'ed kernel will skip these pages and fill in zero data for the reader of vmcore. The dump tool like makedumpfile creates a page descriptor (size 24 bytes) for each non-free page, including zero data page, but it will not create descriptor for free pages. If it is not able to distinguish these unaccepted pages with zero data pages, a certain amount of space will be wasted in proportion (~1/170). In fact, as a special kind of free page the unaccepted pages should be excluded, like the real free pages. Export the page type PAGE_UNACCEPTED_MAPCOUNT_VALUE to vmcoreinfo, so that dump tool can identify whether a page is unaccepted. [zhiquan1.li@intel.com: fix docs: "Title underline too short" warning] Link: https://lore.kernel.org/all/20240809114854.3745464-5-kirill.shutemov@linux.intel.com/ Link: https://lkml.kernel.org/r/20250405060610.860465-1-zhiquan1.li@intel.com Link: https://lore.kernel.org/all/20240809114854.3745464-5-kirill.shutemov@linux.intel.com/ Link: https://lkml.kernel.org/r/20250403030801.758687-1-zhiquan1.li@intel.com Signed-off-by: Zhiquan Li Reviewed-by: Kirill A. Shutemov Acked-by: Baoquan He Cc: Dave Young Cc: Vivek Goyal Cc: Zhiquan Li Signed-off-by: Andrew Morton

x86/mm: Remove CONFIG_HIGHMEM64G support

2025-02-27T10:21:53+00:00

HIGHMEM64G support was added in linux-2.3.25 to support (then) high-end Pentium Pro and Pentium III Xeon servers with more than 4GB of addressing, NUMA and PCI-X slots started appearing. I have found no evidence of this ever being used in regular dual-socket servers or consumer devices, all the users seem obsolete these days, even by i386 standards: - Support for NUMA servers (NUMA-Q, IBM x440, unisys) was already removed ten years ago. - 4+ socket non-NUMA servers based on Intel 450GX/450NX, HP F8 and ServerWorks ServerSet/GrandChampion could theoretically still work with 8GB, but these were exceptionally rare even 20 years ago and would have usually been equipped with than the maximum amount of RAM. - Some SKUs of the Celeron D from 2004 had 64-bit mode fused off but could still work in a Socket 775 mainboard designed for the later Core 2 Duo and 8GB. Apparently most BIOSes at the time only allowed 64-bit CPUs. - The rare Xeon LV "Sossaman" came on a few motherboards with registered DDR2 memory support up to 16GB. - In the early days of x86-64 hardware, there was sometimes the need to run a 32-bit kernel to work around bugs in the hardware drivers, or in the syscall emulation for 32-bit userspace. This likely still works but there should never be a need for this any more. PAE mode is still required to get access to the 'NX' bit on Atom 'Pentium M' and 'Core Duo' CPUs. Signed-off-by: Arnd Bergmann Signed-off-by: Ingo Molnar Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250226213714.4040853-6-arnd@kernel.org

Documentation: kdump: clean up the outdated description

2024-04-26T04:07:04+00:00

After commit 443cbaf9e2fd ("crash: split vmcoreinfo exporting code out from crash_core.c"), Kconfig item CRASH_CORE has gone away in kernel. Items VMCORE_INFO and CRASH_RESERVE are used instead. So clean up the outdated description about CRASH_CORE and update it accordingly. Link: https://lkml.kernel.org/r/20240329132825.1102459-3-bhe@redhat.com Signed-off-by: Baoquan He Cc: Jonathan Corbet Cc: Geert Uytterhoeven Cc: Huacai Chen Cc: WANG Xuerui Signed-off-by: Andrew Morton