On 2024/3/26 13:54, Sourabh Jain wrote:
> Commit 247262756121 ("crash: add generic infrastructure for crash
> hotplug support") added a generic infrastructure that allows
> architectures to selectively update the kdump image component during CPU
> or memory add/remove events within the kernel itself.
>
> This patch series adds crash hotplug handler for PowerPC and enable
> support to update the kdump image on CPU/Memory add/remove events.
>
> Among the 6 patches in this series, the first two patches make changes
> to the generic crash hotplug handler to assist PowerPC in adding support
> for this feature. The last four patches add support for this feature.
>
> The following section outlines the problem addressed by this patch
> series, along with the current solution, its shortcomings, and the
> proposed resolution.
>
> Problem:
> ========
> Due to CPU/Memory hotplug or online/offline events the elfcorehdr
> (which describes the CPUs and memory of the crashed kernel) and FDT
> (Flattened Device Tree) of kdump image becomes outdated. Consequently,
> attempting dump collection with an outdated elfcorehdr or FDT can lead
> to failed or inaccurate dump collection.
Hi, Sourabh, are there any specific methods to reproduce the scenarios
for this feature? I would like to port this feature to ARM64, but I
don't know how to reproduce the issue.
>
> Going forward CPU hotplug or online/offline events are referred as
> CPU/Memory add/remove events.
>
> Existing solution and its shortcoming:
> ======================================
> The current solution to address the above issue involves monitoring the
> CPU/memory add/remove events in userspace using udev rules and whenever
> there are changes in CPU and memory resources, the entire kdump image
> is loaded again. The kdump image includes kernel, initrd, elfcorehdr,
> FDT, purgatory. Given that only elfcorehdr and FDT get outdated due to
> CPU/Memory add/remove events, reloading the entire kdump image is
> inefficient. More importantly, kdump remains inactive for a substantial
> amount of time until the kdump reload completes.
>
> Proposed solution:
> ==================
> Instead of initiating a full kdump image reload from userspace on
> CPU/Memory hotplug and online/offline events, the proposed solution aims
> to update only the necessary kdump image component within the kernel
> itself.
>
> Git tree for testing:
> =====================
> https://github.com/sourabhjains/linux/tree/kdump-in-kernel-crash-update-v18
>
> Above tree is rebased on top of powerpc/next branch.
>
> To realize this feature, the kdump udev rule must be updated. On RHEL,
> add the following two lines at the top of the
> "/usr/lib/udev/rules.d/98-kexec.rules" file.
>
> SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
> SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
>
> With the above change to the kdump udev rule, kdump reload is avoided
> during CPU/Memory add/remove events if this feature is enabled in the
> kernel.
>
> Note: only kexec_file_load syscall will work. For kexec_load minor changes
> are required in kexec tool.
>
> Changelog:
> ----------
> v18: [No functional changes]
> - Update a comment in 2/6.
> - Describe the clean-up done on x86 in patch description 2/6.
> - Fix a minor typo in the patch description of 3/6.
>
> v17: [https://lore.kernel.org/all/20240226084118.16310-1-sourabhjain@xxxxxxxxxxxxx/]
> - Rebase the patch series on top linux-next tree and below patch series
> https://lore.kernel.org/all/20240213113150.1148276-1-hbathini@xxxxxxxxxxxxx/
> - Split 0003 patch from v16 into two patches
> 1. Move get_crash_memory_ranges() along with other *_memory_ranges()
> functions to ranges.c and make them public.
> 2. Make update_cpus_node function public and take this function
> out of file_load_64.c
> - Keep arch_crash_hotplug_support in crash.c instead of core_64.c [05/06]
> - Use CONFIG_CRASH_MAX_MEMORY_RANGES to find extra elfcorehdr size [06/06]
>
> v16: [https://lore.kernel.org/all/20240217081452.164571-1-sourabhjain@xxxxxxxxxxxxx/]
> - Remove the unused #define `crash_hotplug_cpu_support`
> and `crash_hotplug_memory_support` in `arch/x86/include/asm/kexec.h`.
> - Document why two kexec flag bits are used in
> `arch_crash_hotplug_memory_support` (x86).
> - Use a switch case to handle different hotplug operations
> in `arch_crash_handle_hotplug_event` for PowerPC.
> - Fix a typo in 4/5.
>
> v15:
> - Remove the patch that adds a new kexec flag for FDT update.
> - Introduce a generic kexec flag bit to share hotplug support
> intent between the kexec tool and the kernel for the kexec_load
> syscall. (2/5)
> - Introduce an architecture-specific handler to process the kexec
> flag for crash hotplug support. (2/5)
> - Rename the @update_elfcorehdr member of the struct kimage to
> @hotplug_support. (2/5)
> - Use a common function to advertise hotplug support for both CPU
> and Memory. (2/5)
>
> v14:
> - Fix build warnings by including necessary header files
> - Rebase to v6.7-rc5
>
> v13:
> - Fix a build warning, take ranges.c out of CONFIG_KEXEC_FILE
> - Rebase to v6.7-rc4
>
> v12:
> - A patch to add new kexec flags to support this feature on kexec_load
> system call
> - Change in the way this feature is advertise to userspace for both
> kexec_load syscall
> - Rebase to v6.6-rc7
>
> v11:
> - Rebase to v6.4-rc6
> - The patch that introduced CONFIG_CRASH_HOTPLUG for PowerPC has been
> removed. The config is now part of common configuration:
> https://lore.kernel.org/all/87ilbpflsk.fsf@mail.lhotse/
>
> v10:
> - Drop the patch that adds fdt_index attribute to struct kimage_arch
> Find the fdt segment index when needed.
> - Added more details into commits messages.
> - Rebased onto 6.3.0-rc5
>
> v9:
> - Removed patch to prepare elfcorehdr crash notes for possible CPUs.
> The patch is moved to generic patch series that introduces generic
> infrastructure for in kernel crash update.
> - Removed patch to pass the hotplug action type to the arch crash
> hotplug handler function. The generic patch series has introduced
> the hotplug action type in kimage struct.
> - Add detail commit message for better understanding.
>
> v8:
> - Restrict fdt_index initialization to machine_kexec_post_load
> it work for both kexec_load and kexec_file_load.[3/8] Laurent Dufour
>
> - Updated the logic to find the number of offline core. [6/8]
>
> - Changed the logic to find the elfcore program header to accommodate
> future memory ranges due memory hotplug events. [8/8]
>
> v7
> - added a new config to configure this feature
> - pass hotplug action type to arch specific handler
>
> v6
> - Added crash memory hotplug support
>
> v5:
> - Replace COFNIG_CRASH_HOTPLUG with CONFIG_HOTPLUG_CPU.
> - Move fdt segment identification for kexec_load case to load path
> instead of crash hotplug handler
> - Keep new attribute defined under kimage_arch to track FDT segment
> under CONFIG_HOTPLUG_CPU config.
>
> v4:
> - Update the logic to find the additional space needed for hotadd CPUs
> post kexec load. Refer "[RFC v4 PATCH 4/5] powerpc/crash hp: add crash
> hotplug support for kexec_file_load" patch to know more about the
> change.
> - Fix a couple of typo.
> - Replace pr_err to pr_info_once to warn user about memory hotplug
> support.
> - In crash hotplug handle exit the for loop if FDT segment is found.
>
> v3
> - Move fdt_index and fdt_index_vaild variables to kimage_arch struct.
> - Rebase patche on top of
> https://lore.kernel.org/lkml/20220303162725.49640-1-eric.devolder@xxxxxxxxxx/
> - Fixed warning reported by checpatch script
>
> v2:
> - Use generic hotplug handler introduced by
> https://lore.kernel.org/lkml/20220209195706.51522-1-eric.devolder@xxxxxxxxxx/
> a significant change from v1.
>
> Cc: Akhil Raj <lf32.dev@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxx>
> Cc: Baoquan He <bhe@xxxxxxxxxx>
> Cc: Borislav Petkov (AMD) <bp@xxxxxxxxx>
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Dave Young <dyoung@xxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Hari Bathini <hbathini@xxxxxxxxxxxxx>
> Cc: Laurent Dufour <laurent.dufour@xxxxxxxxxx>
> Cc: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> Cc: Naveen N Rao <naveen@xxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> Cc: kexec@xxxxxxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx
>
> Sourabh Jain (6):
> crash: forward memory_notify arg to arch crash hotplug handler
> crash: add a new kexec flag for hotplug support
> powerpc/kexec: move *_memory_ranges functions to ranges.c
> PowerPC/kexec: make the update_cpus_node() function public
> powerpc/crash: add crash CPU hotplug support
> powerpc/crash: add crash memory hotplug support
>
> arch/powerpc/Kconfig | 4 +
> arch/powerpc/include/asm/kexec.h | 15 ++
> arch/powerpc/include/asm/kexec_ranges.h | 20 +-
> arch/powerpc/kexec/Makefile | 4 +-
> arch/powerpc/kexec/core_64.c | 91 +++++++
> arch/powerpc/kexec/crash.c | 196 +++++++++++++++
> arch/powerpc/kexec/elf_64.c | 3 +-
> arch/powerpc/kexec/file_load_64.c | 314 +++---------------------
> arch/powerpc/kexec/ranges.c | 312 ++++++++++++++++++++++-
> arch/x86/include/asm/kexec.h | 13 +-
> arch/x86/kernel/crash.c | 32 ++-
> drivers/base/cpu.c | 2 +-
> drivers/base/memory.c | 2 +-
> include/linux/crash_core.h | 15 +-
> include/linux/kexec.h | 11 +-
> include/uapi/linux/kexec.h | 1 +
> kernel/crash_core.c | 29 +--
> kernel/kexec.c | 4 +-
> kernel/kexec_file.c | 5 +
> 19 files changed, 714 insertions(+), 359 deletions(-)
>
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