kernel/linux.git/include/linux/kexec.h, branch linux-6.9.y

kexec: fix the unexpected kexec_dprintk() macro

2024-06-21T12:40:33+00:00

commit f4af41bf177add167e39e4b0203460b1d0b531f6 upstream. Jiri reported that the current kexec_dprintk() always prints out debugging message whenever kexec/kdmmp loading is triggered. That is not wanted. The debugging message is supposed to be printed out when 'kexec -s -d' is specified for kexec/kdump loading. After investigating, the reason is the current kexec_dprintk() takes printk(KERN_INFO) or printk(KERN_DEBUG) depending on whether '-d' is specified. However, distros usually have defaulg log level like below: [~]# cat /proc/sys/kernel/printk 7 4 1 7 So, even though '-d' is not specified, printk(KERN_DEBUG) also always prints out. I thought printk(KERN_DEBUG) is equal to pr_debug(), it's not. Fix it by changing to use pr_info() instead which are expected to work. Link: https://lkml.kernel.org/r/20240409042238.1240462-1-bhe@redhat.com Fixes: cbc2fe9d9cb2 ("kexec_file: add kexec_file flag to control debug printing") Signed-off-by: Baoquan He Reported-by: Jiri Slaby Closes: https://lore.kernel.org/all/4c775fca-5def-4a2d-8437-7130b02722a2@kernel.org Reviewed-by: Dave Young Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

crash: split crash dumping code out from kexec_core.c

2024-02-24T01:48:22+00:00

Currently, KEXEC_CORE select CRASH_CORE automatically because crash codes need be built in to avoid compiling error when building kexec code even though the crash dumping functionality is not enabled. E.g -------------------- CONFIG_CRASH_CORE=y CONFIG_KEXEC_CORE=y CONFIG_KEXEC=y CONFIG_KEXEC_FILE=y --------------------- After splitting out crashkernel reservation code and vmcoreinfo exporting code, there's only crash related code left in kernel/crash_core.c. Now move crash related codes from kexec_core.c to crash_core.c and only build it in when CONFIG_CRASH_DUMP=y. And also wrap up crash codes inside CONFIG_CRASH_DUMP ifdeffery scope, or replace inappropriate CONFIG_KEXEC_CORE ifdef with CONFIG_CRASH_DUMP ifdef in generic kernel files. With these changes, crash_core codes are abstracted from kexec codes and can be disabled at all if only kexec reboot feature is wanted. Link: https://lkml.kernel.org/r/20240124051254.67105-5-bhe@redhat.com Signed-off-by: Baoquan He Cc: Al Viro Cc: Eric W. Biederman Cc: Hari Bathini Cc: Pingfan Liu Cc: Klara Modin Cc: Michael Kelley Cc: Nathan Chancellor Cc: Stephen Rothwell Cc: Yang Li Signed-off-by: Andrew Morton

crash: split vmcoreinfo exporting code out from crash_core.c

2024-02-24T01:48:22+00:00

Now move the relevant codes into separate files: kernel/crash_reserve.c, include/linux/crash_reserve.h. And add config item CRASH_RESERVE to control its enabling. And also update the old ifdeffery of CONFIG_CRASH_CORE, including of and config item dependency on CRASH_CORE accordingly. And also do renaming as follows: - arch/xxx/kernel/{crash_core.c => vmcore_info.c} because they are only related to vmcoreinfo exporting on x86, arm64, riscv. And also Remove config item CRASH_CORE, and rely on CONFIG_KEXEC_CORE to decide if build in crash_core.c. [yang.lee@linux.alibaba.com: remove duplicated include in vmcore_info.c] Link: https://lkml.kernel.org/r/20240126005744.16561-1-yang.lee@linux.alibaba.com Link: https://lkml.kernel.org/r/20240124051254.67105-3-bhe@redhat.com Signed-off-by: Baoquan He Signed-off-by: Yang Li Acked-by: Hari Bathini Cc: Al Viro Cc: Eric W. Biederman Cc: Pingfan Liu Cc: Klara Modin Cc: Michael Kelley Cc: Nathan Chancellor Cc: Stephen Rothwell Cc: Yang Li Signed-off-by: Andrew Morton

kexec: split crashkernel reservation code out from crash_core.c

2024-02-24T01:48:21+00:00

Patch series "Split crash out from kexec and clean up related config items", v3. Motivation: ============= Previously, LKP reported a building error. When investigating, it can't be resolved reasonablly with the present messy kdump config items. https://lore.kernel.org/oe-kbuild-all/202312182200.Ka7MzifQ-lkp@intel.com/ The kdump (crash dumping) related config items could causes confusions: Firstly, CRASH_CORE enables codes including - crashkernel reservation; - elfcorehdr updating; - vmcoreinfo exporting; - crash hotplug handling; Now fadump of powerpc, kcore dynamic debugging and kdump all selects CRASH_CORE, while fadump - fadump needs crashkernel parsing, vmcoreinfo exporting, and accessing global variable 'elfcorehdr_addr'; - kcore only needs vmcoreinfo exporting; - kdump needs all of the current kernel/crash_core.c. So only enabling PROC_CORE or FA_DUMP will enable CRASH_CORE, this mislead people that we enable crash dumping, actual it's not. Secondly, It's not reasonable to allow KEXEC_CORE select CRASH_CORE. Because KEXEC_CORE enables codes which allocate control pages, copy kexec/kdump segments, and prepare for switching. These codes are shared by both kexec reboot and kdump. We could want kexec reboot, but disable kdump. In that case, CRASH_CORE should not be selected. -------------------- CONFIG_CRASH_CORE=y CONFIG_KEXEC_CORE=y CONFIG_KEXEC=y CONFIG_KEXEC_FILE=y --------------------- Thirdly, It's not reasonable to allow CRASH_DUMP select KEXEC_CORE. That could make KEXEC_CORE, CRASH_DUMP are enabled independently from KEXEC or KEXEC_FILE. However, w/o KEXEC or KEXEC_FILE, the KEXEC_CORE code built in doesn't make any sense because no kernel loading or switching will happen to utilize the KEXEC_CORE code. --------------------- CONFIG_CRASH_CORE=y CONFIG_KEXEC_CORE=y CONFIG_CRASH_DUMP=y --------------------- In this case, what is worse, on arch sh and arm, KEXEC relies on MMU, while CRASH_DUMP can still be enabled when !MMU, then compiling error is seen as the lkp test robot reported in above link. ------arch/sh/Kconfig------ config ARCH_SUPPORTS_KEXEC def_bool MMU config ARCH_SUPPORTS_CRASH_DUMP def_bool BROKEN_ON_SMP --------------------------- Changes: =========== 1, split out crash_reserve.c from crash_core.c; 2, split out vmcore_infoc. from crash_core.c; 3, move crash related codes in kexec_core.c into crash_core.c; 4, remove dependency of FA_DUMP on CRASH_DUMP; 5, clean up kdump related config items; 6, wrap up crash codes in crash related ifdefs on all 8 arch-es which support crash dumping, except of ppc; Achievement: =========== With above changes, I can rearrange the config item logic as below (the right item depends on or is selected by the left item): PROC_KCORE -----------> VMCORE_INFO |----------> VMCORE_INFO FA_DUMP----| |----------> CRASH_RESERVE ---->VMCORE_INFO / |---->CRASH_RESERVE KEXEC --| /| |--> KEXEC_CORE--> CRASH_DUMP-->/-|---->PROC_VMCORE KEXEC_FILE --| \ | \---->CRASH_HOTPLUG KEXEC --| |--> KEXEC_CORE (for kexec reboot only) KEXEC_FILE --| Test ======== On all 8 architectures, including x86_64, arm64, s390x, sh, arm, mips, riscv, loongarch, I did below three cases of config item setting and building all passed. Take configs on x86_64 as exampmle here: (1) Both CONFIG_KEXEC and KEXEC_FILE is unset, then all kexec/kdump items are unset automatically: # Kexec and crash features # CONFIG_KEXEC is not set # CONFIG_KEXEC_FILE is not set # end of Kexec and crash features (2) set CONFIG_KEXEC_FILE and 'make olddefconfig': --------------- # Kexec and crash features CONFIG_CRASH_RESERVE=y CONFIG_VMCORE_INFO=y CONFIG_KEXEC_CORE=y CONFIG_KEXEC_FILE=y CONFIG_CRASH_DUMP=y CONFIG_CRASH_HOTPLUG=y CONFIG_CRASH_MAX_MEMORY_RANGES=8192 # end of Kexec and crash features --------------- (3) unset CONFIG_CRASH_DUMP in case 2 and execute 'make olddefconfig': ------------------------ # Kexec and crash features CONFIG_KEXEC_CORE=y CONFIG_KEXEC_FILE=y # end of Kexec and crash features ------------------------ Note: For ppc, it needs investigation to make clear how to split out crash code in arch folder. Hope Hari and Pingfan can help have a look, see if it's doable. Now, I make it either have both kexec and crash enabled, or disable both of them altogether. This patch (of 14): Both kdump and fa_dump of ppc rely on crashkernel reservation. Move the relevant codes into separate files: crash_reserve.c, include/linux/crash_reserve.h. And also add config item CRASH_RESERVE to control its enabling of the codes. And update config items which has relationship with crashkernel reservation. And also change ifdeffery from CONFIG_CRASH_CORE to CONFIG_CRASH_RESERVE when those scopes are only crashkernel reservation related. And also rename arch/XXX/include/asm/{crash_core.h => crash_reserve.h} on arm64, x86 and risc-v because those architectures' crash_core.h is only related to crashkernel reservation. [akpm@linux-foundation.org: s/CRASH_RESEERVE/CRASH_RESERVE/, per Klara Modin] Link: https://lkml.kernel.org/r/20240124051254.67105-1-bhe@redhat.com Link: https://lkml.kernel.org/r/20240124051254.67105-2-bhe@redhat.com Signed-off-by: Baoquan He Acked-by: Hari Bathini Cc: Al Viro Cc: Eric W. Biederman Cc: Pingfan Liu Cc: Klara Modin Cc: Michael Kelley Cc: Nathan Chancellor Cc: Stephen Rothwell Cc: Yang Li Signed-off-by: Andrew Morton

kexec_file: add kexec_file flag to control debug printing

2023-12-20T23:02:57+00:00

Patch series "kexec_file: print out debugging message if required", v4. Currently, specifying '-d' on kexec command will print a lot of debugging informationabout kexec/kdump loading with kexec_load interface. However, kexec_file_load prints nothing even though '-d' is specified. It's very inconvenient to debug or analyze the kexec/kdump loading when something wrong happened with kexec/kdump itself or develper want to check the kexec/kdump loading. In this patchset, a kexec_file flag is KEXEC_FILE_DEBUG added and checked in code. If it's passed in, debugging message of kexec_file code will be printed out and can be seen from console and dmesg. Otherwise, the debugging message is printed like beofre when pr_debug() is taken. Note: **** ===== 1) The code in kexec-tools utility also need be changed to support passing KEXEC_FILE_DEBUG to kernel when 'kexec -s -d' is specified. The patch link is here: ========= [PATCH] kexec_file: add kexec_file flag to support debug printing http://lists.infradead.org/pipermail/kexec/2023-November/028505.html 2) s390 also has kexec_file code, while I am not sure what debugging information is necessary. So leave it to s390 developer. Test: **** ==== Testing was done in v1 on x86_64 and arm64. For v4, tested on x86_64 again. And on x86_64, the printed messages look like below: -------------------------------------------------------------- kexec measurement buffer for the loaded kernel at 0x207fffe000. Loaded purgatory at 0x207fff9000 Loaded boot_param, command line and misc at 0x207fff3000 bufsz=0x1180 memsz=0x1180 Loaded 64bit kernel at 0x207c000000 bufsz=0xc88200 memsz=0x3c4a000 Loaded initrd at 0x2079e79000 bufsz=0x2186280 memsz=0x2186280 Final command line is: root=/dev/mapper/fedora_intel--knightslanding--lb--02-root ro rd.lvm.lv=fedora_intel-knightslanding-lb-02/root console=ttyS0,115200N81 crashkernel=256M E820 memmap: 0000000000000000-000000000009a3ff (1) 000000000009a400-000000000009ffff (2) 00000000000e0000-00000000000fffff (2) 0000000000100000-000000006ff83fff (1) 000000006ff84000-000000007ac50fff (2) ...... 000000207fff6150-000000207fff615f (128) 000000207fff6160-000000207fff714f (1) 000000207fff7150-000000207fff715f (128) 000000207fff7160-000000207fff814f (1) 000000207fff8150-000000207fff815f (128) 000000207fff8160-000000207fffffff (1) nr_segments = 5 segment[0]: buf=0x000000004e5ece74 bufsz=0x211 mem=0x207fffe000 memsz=0x1000 segment[1]: buf=0x000000009e871498 bufsz=0x4000 mem=0x207fff9000 memsz=0x5000 segment[2]: buf=0x00000000d879f1fe bufsz=0x1180 mem=0x207fff3000 memsz=0x2000 segment[3]: buf=0x000000001101cd86 bufsz=0xc88200 mem=0x207c000000 memsz=0x3c4a000 segment[4]: buf=0x00000000c6e38ac7 bufsz=0x2186280 mem=0x2079e79000 memsz=0x2187000 kexec_file_load: type:0, start:0x207fff91a0 head:0x109e004002 flags:0x8 --------------------------------------------------------------------------- This patch (of 7): When specifying 'kexec -c -d', kexec_load interface will print loading information, e.g the regions where kernel/initrd/purgatory/cmdline are put, the memmap passed to 2nd kernel taken as system RAM ranges, and printing all contents of struct kexec_segment, etc. These are very helpful for analyzing or positioning what's happening when kexec/kdump itself failed. The debugging printing for kexec_load interface is made in user space utility kexec-tools. Whereas, with kexec_file_load interface, 'kexec -s -d' print nothing. Because kexec_file code is mostly implemented in kernel space, and the debugging printing functionality is missed. It's not convenient when debugging kexec/kdump loading and jumping with kexec_file_load interface. Now add KEXEC_FILE_DEBUG to kexec_file flag to control the debugging message printing. And add global variable kexec_file_dbg_print and macro kexec_dprintk() to facilitate the printing. This is a preparation, later kexec_dprintk() will be used to replace the existing pr_debug(). Once 'kexec -s -d' is specified, it will print out kexec/kdump loading information. If '-d' is not specified, it regresses to pr_debug(). Link: https://lkml.kernel.org/r/20231213055747.61826-1-bhe@redhat.com Link: https://lkml.kernel.org/r/20231213055747.61826-2-bhe@redhat.com Signed-off-by: Baoquan He Cc: Conor Dooley Cc: Joe Perches Cc: Nathan Chancellor Signed-off-by: Andrew Morton

crash_core: move crashk_*res definition into crash_core.c

2023-10-04T17:41:58+00:00

Both crashk_res and crashk_low_res are used to mark the reserved crashkernel regions in iomem_resource tree. And later the generic crashkernel resrvation will be added into crash_core.c. So move crashk_res and crashk_low_res definition into crash_core.c to avoid compiling error if CONFIG_CRASH_CORE=on while CONFIG_KEXEC_CORE is unset. Meanwhile include in if generic reservation is needed. In that case, need be added by ARCH. In asm/crash_core.h, ARCH can provide its own macro definitions to override macros in if needed. Wrap the including into CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION ifdeffery scope to avoid compiling error in other ARCH-es which don't take the generic reservation way yet. Link: https://lkml.kernel.org/r/20230914033142.676708-6-bhe@redhat.com Signed-off-by: Baoquan He Reviewed-by: Zhen Lei Cc: Catalin Marinas Cc: Chen Jiahao Signed-off-by: Andrew Morton

crash: hotplug support for kexec_load()

2023-08-24T23:25:14+00:00

The hotplug support for kexec_load() requires changes to the userspace kexec-tools and a little extra help from the kernel. Given a kdump capture kernel loaded via kexec_load(), and a subsequent hotplug event, the crash hotplug handler finds the elfcorehdr and rewrites it to reflect the hotplug change. That is the desired outcome, however, at kernel panic time, the purgatory integrity check fails (because the elfcorehdr changed), and the capture kernel does not boot and no vmcore is generated. Therefore, the userspace kexec-tools/kexec must indicate to the kernel that the elfcorehdr can be modified (because the kexec excluded the elfcorehdr from the digest, and sized the elfcorehdr memory buffer appropriately). To facilitate hotplug support with kexec_load(): - a new kexec flag KEXEC_UPATE_ELFCOREHDR indicates that it is safe for the kernel to modify the kexec_load()'d elfcorehdr - the /sys/kernel/crash_elfcorehdr_size node communicates the preferred size of the elfcorehdr memory buffer - The sysfs crash_hotplug nodes (ie. /sys/devices/system/[cpu|memory]/crash_hotplug) dynamically take into account kexec_file_load() vs kexec_load() and KEXEC_UPDATE_ELFCOREHDR. This is critical so that the udev rule processing of crash_hotplug is all that is needed to determine if the userspace unload-then-load of the kdump image is to be skipped, or not. The proposed udev rule change looks like: # The kernel updates the crash elfcorehdr for CPU and memory changes SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" The table below indicates the behavior of kexec_load()'d kdump image updates (with the new udev crash_hotplug rule in place): Kernel |Kexec -------+-----+---- Old |Old |New | a | a -------+-----+---- New | a | b -------+-----+---- where kexec 'old' and 'new' delineate kexec-tools has the needed modifications for the crash hotplug feature, and kernel 'old' and 'new' delineate the kernel supports this crash hotplug feature. Behavior 'a' indicates the unload-then-reload of the entire kdump image. For the kexec 'old' column, the unload-then-reload occurs due to the missing flag KEXEC_UPDATE_ELFCOREHDR. An 'old' kernel (with 'new' kexec) does not present the crash_hotplug sysfs node, which leads to the unload-then-reload of the kdump image. Behavior 'b' indicates the desired optimized behavior of the kernel directly modifying the elfcorehdr and avoiding the unload-then-reload of the kdump image. If the udev rule is not updated with crash_hotplug node check, then no matter any combination of kernel or kexec is new or old, the kdump image continues to be unload-then-reload on hotplug changes. To fully support crash hotplug feature, there needs to be a rollout of kernel, kexec-tools and udev rule changes. However, the order of the rollout of these pieces does not matter; kexec_load()'d kdump images still function for hotplug as-is. Link: https://lkml.kernel.org/r/20230814214446.6659-7-eric.devolder@oracle.com Signed-off-by: Eric DeVolder Suggested-by: Hari Bathini Acked-by: Hari Bathini Acked-by: Baoquan He Cc: Akhil Raj Cc: Bjorn Helgaas Cc: Borislav Petkov (AMD) Cc: Boris Ostrovsky Cc: Dave Hansen Cc: Dave Young Cc: David Hildenbrand Cc: Eric W. Biederman Cc: Greg Kroah-Hartman Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jonathan Corbet Cc: Konrad Rzeszutek Wilk Cc: Mimi Zohar Cc: Naveen N. Rao Cc: Oscar Salvador Cc: "Rafael J. Wysocki" Cc: Sean Christopherson Cc: Sourabh Jain Cc: Takashi Iwai Cc: Thomas Gleixner Cc: Thomas Weißschuh Cc: Valentin Schneider Cc: Vivek Goyal Cc: Vlastimil Babka Signed-off-by: Andrew Morton

crash: memory and CPU hotplug sysfs attributes

2023-08-24T23:25:14+00:00

Introduce the crash_hotplug attribute for memory and CPUs for use by userspace. These attributes directly facilitate the udev rule for managing userspace re-loading of the crash kernel upon hot un/plug changes. For memory, expose the crash_hotplug attribute to the /sys/devices/system/memory directory. For example: # udevadm info --attribute-walk /sys/devices/system/memory/memory81 looking at device '/devices/system/memory/memory81': KERNEL=="memory81" SUBSYSTEM=="memory" DRIVER=="" ATTR{online}=="1" ATTR{phys_device}=="0" ATTR{phys_index}=="00000051" ATTR{removable}=="1" ATTR{state}=="online" ATTR{valid_zones}=="Movable" looking at parent device '/devices/system/memory': KERNELS=="memory" SUBSYSTEMS=="" DRIVERS=="" ATTRS{auto_online_blocks}=="offline" ATTRS{block_size_bytes}=="8000000" ATTRS{crash_hotplug}=="1" For CPUs, expose the crash_hotplug attribute to the /sys/devices/system/cpu directory. For example: # udevadm info --attribute-walk /sys/devices/system/cpu/cpu0 looking at device '/devices/system/cpu/cpu0': KERNEL=="cpu0" SUBSYSTEM=="cpu" DRIVER=="processor" ATTR{crash_notes}=="277c38600" ATTR{crash_notes_size}=="368" ATTR{online}=="1" looking at parent device '/devices/system/cpu': KERNELS=="cpu" SUBSYSTEMS=="" DRIVERS=="" ATTRS{crash_hotplug}=="1" ATTRS{isolated}=="" ATTRS{kernel_max}=="8191" ATTRS{nohz_full}==" (null)" ATTRS{offline}=="4-7" ATTRS{online}=="0-3" ATTRS{possible}=="0-7" ATTRS{present}=="0-3" With these sysfs attributes in place, it is possible to efficiently instruct the udev rule to skip crash kernel reloading for kernels configured with crash hotplug support. For example, the following is the proposed udev rule change for RHEL system 98-kexec.rules (as the first lines of the rule file): # The kernel updates the crash elfcorehdr for CPU and memory changes SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" When examined in the context of 98-kexec.rules, the above rules test if crash_hotplug is set, and if so, the userspace initiated unload-then-reload of the crash kernel is skipped. CPU and memory checks are separated in accordance with CONFIG_HOTPLUG_CPU and CONFIG_MEMORY_HOTPLUG kernel config options. If an architecture supports, for example, memory hotplug but not CPU hotplug, then the /sys/devices/system/memory/crash_hotplug attribute file is present, but the /sys/devices/system/cpu/crash_hotplug attribute file will NOT be present. Thus the udev rule skips userspace processing of memory hot un/plug events, but the udev rule will evaluate false for CPU events, thus allowing userspace to process CPU hot un/plug events (ie the unload-then-reload of the kdump capture kernel). Link: https://lkml.kernel.org/r/20230814214446.6659-5-eric.devolder@oracle.com Signed-off-by: Eric DeVolder Reviewed-by: Sourabh Jain Acked-by: Hari Bathini Acked-by: Baoquan He Cc: Akhil Raj Cc: Bjorn Helgaas Cc: Borislav Petkov (AMD) Cc: Boris Ostrovsky Cc: Dave Hansen Cc: Dave Young Cc: David Hildenbrand Cc: Eric W. Biederman Cc: Greg Kroah-Hartman Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jonathan Corbet Cc: Konrad Rzeszutek Wilk Cc: Mimi Zohar Cc: Naveen N. Rao Cc: Oscar Salvador Cc: "Rafael J. Wysocki" Cc: Sean Christopherson Cc: Takashi Iwai Cc: Thomas Gleixner Cc: Thomas Weißschuh Cc: Valentin Schneider Cc: Vivek Goyal Cc: Vlastimil Babka Signed-off-by: Andrew Morton

crash: add generic infrastructure for crash hotplug support

2023-08-24T23:25:13+00:00

To support crash hotplug, a mechanism is needed to update the crash elfcorehdr upon CPU or memory changes (eg. hot un/plug or off/ onlining). The crash elfcorehdr describes the CPUs and memory to be written into the vmcore. To track CPU changes, callbacks are registered with the cpuhp mechanism via cpuhp_setup_state_nocalls(CPUHP_BP_PREPARE_DYN). The crash hotplug elfcorehdr update has no explicit ordering requirement (relative to other cpuhp states), so meets the criteria for utilizing CPUHP_BP_PREPARE_DYN. CPUHP_BP_PREPARE_DYN is a dynamic state and avoids the need to introduce a new state for crash hotplug. Also, CPUHP_BP_PREPARE_DYN is the last state in the PREPARE group, just prior to the STARTING group, which is very close to the CPU starting up in a plug/online situation, or stopping in a unplug/ offline situation. This minimizes the window of time during an actual plug/online or unplug/offline situation in which the elfcorehdr would be inaccurate. Note that for a CPU being unplugged or offlined, the CPU will still be present in the list of CPUs generated by crash_prepare_elf64_headers(). However, there is no need to explicitly omit the CPU, see justification in 'crash: change crash_prepare_elf64_headers() to for_each_possible_cpu()'. To track memory changes, a notifier is registered to capture the memblock MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier(). The CPU callbacks and memory notifiers invoke crash_handle_hotplug_event() which performs needed tasks and then dispatches the event to the architecture specific arch_crash_handle_hotplug_event() to update the elfcorehdr with the current state of CPUs and memory. During the process, the kexec_lock is held. Link: https://lkml.kernel.org/r/20230814214446.6659-3-eric.devolder@oracle.com Signed-off-by: Eric DeVolder Reviewed-by: Sourabh Jain Acked-by: Hari Bathini Acked-by: Baoquan He Cc: Akhil Raj Cc: Bjorn Helgaas Cc: Borislav Petkov (AMD) Cc: Boris Ostrovsky Cc: Dave Hansen Cc: Dave Young Cc: David Hildenbrand Cc: Eric W. Biederman Cc: Greg Kroah-Hartman Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jonathan Corbet Cc: Konrad Rzeszutek Wilk Cc: Mimi Zohar Cc: Naveen N. Rao Cc: Oscar Salvador Cc: "Rafael J. Wysocki" Cc: Sean Christopherson Cc: Takashi Iwai Cc: Thomas Gleixner Cc: Thomas Weißschuh Cc: Valentin Schneider Cc: Vivek Goyal Cc: Vlastimil Babka Signed-off-by: Andrew Morton

crash: move a few code bits to setup support of crash hotplug

2023-08-24T23:25:13+00:00

Patch series "crash: Kernel handling of CPU and memory hot un/plug", v28. Once the kdump service is loaded, if changes to CPUs or memory occur, either by hot un/plug or off/onlining, the crash elfcorehdr must also be updated. The elfcorehdr describes to kdump the CPUs and memory in the system, and any inaccuracies can result in a vmcore with missing CPU context or memory regions. The current solution utilizes udev to initiate an unload-then-reload of the kdump image (eg. kernel, initrd, boot_params, purgatory and elfcorehdr) by the userspace kexec utility. In the original post I outlined the significant performance problems related to offloading this activity to userspace. This patchset introduces a generic crash handler that registers with the CPU and memory notifiers. Upon CPU or memory changes, from either hot un/plug or off/onlining, this generic handler is invoked and performs important housekeeping, for example obtaining the appropriate lock, and then invokes an architecture specific handler to do the appropriate elfcorehdr update. Note the description in patch 'crash: change crash_prepare_elf64_headers() to for_each_possible_cpu()' and 'x86/crash: optimize CPU changes' that enables further optimizations related to CPU plug/unplug/online/offline performance of elfcorehdr updates. In the case of x86_64, the arch specific handler generates a new elfcorehdr, and overwrites the old one in memory; thus no involvement with userspace needed. To realize the benefits/test this patchset, one must make a couple of minor changes to userspace: - Prevent udev from updating kdump crash kernel on hot un/plug changes. Add the following as the first lines to the RHEL udev rule file /usr/lib/udev/rules.d/98-kexec.rules: # The kernel updates the crash elfcorehdr for CPU and memory changes SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" With this changeset applied, the two rules evaluate to false for CPU and memory change events and thus skip the userspace unload-then-reload of kdump. - Change to the kexec_file_load for loading the kdump kernel: Eg. on RHEL: in /usr/bin/kdumpctl, change to: standard_kexec_args="-p -d -s" which adds the -s to select kexec_file_load() syscall. This kernel patchset also supports kexec_load() with a modified kexec userspace utility. A working changeset to the kexec userspace utility is posted to the kexec-tools mailing list here: http://lists.infradead.org/pipermail/kexec/2023-May/027049.html To use the kexec-tools patch, apply, build and install kexec-tools, then change the kdumpctl's standard_kexec_args to replace the -s with --hotplug. The removal of -s reverts to the kexec_load syscall and the addition of --hotplug invokes the changes put forth in the kexec-tools patch. This patch (of 8): The crash hotplug support leans on the work for the kexec_file_load() syscall. To also support the kexec_load() syscall, a few bits of code need to be move outside of CONFIG_KEXEC_FILE. As such, these bits are moved out of kexec_file.c and into a common location crash_core.c. In addition, struct crash_mem and crash_notes were moved to new locales so that PROC_KCORE, which sets CRASH_CORE alone, builds correctly. No functionality change intended. Link: https://lkml.kernel.org/r/20230814214446.6659-1-eric.devolder@oracle.com Link: https://lkml.kernel.org/r/20230814214446.6659-2-eric.devolder@oracle.com Signed-off-by: Eric DeVolder Reviewed-by: Sourabh Jain Acked-by: Hari Bathini Acked-by: Baoquan He Cc: Akhil Raj Cc: Bjorn Helgaas Cc: Borislav Petkov (AMD) Cc: Boris Ostrovsky Cc: Dave Hansen Cc: Dave Young Cc: David Hildenbrand Cc: Eric W. Biederman Cc: Greg Kroah-Hartman Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jonathan Corbet Cc: Konrad Rzeszutek Wilk Cc: Mimi Zohar Cc: Naveen N. Rao Cc: Oscar Salvador Cc: "Rafael J. Wysocki" Cc: Sean Christopherson Cc: Takashi Iwai Cc: Thomas Gleixner Cc: Thomas Weißschuh Cc: Valentin Schneider Cc: Vivek Goyal Cc: Vlastimil Babka Signed-off-by: Andrew Morton