kernel.git/arch/x86/kernel/nmi.c, branch linux-rolling-stable

x86: Restrict KVM-induced symbol exports to KVM modules where obvious/possible

2025-11-12T23:29:38Z

Extend KVM's export macro framework to provide EXPORT_SYMBOL_FOR_KVM(), and use the helper macro to export symbols for KVM throughout x86 if and only if KVM will build one or more modules, and only for those modules. To avoid unnecessary exports when CONFIG_KVM=m but kvm.ko will not be built (because no vendor modules are selected), let arch code #define EXPORT_SYMBOL_FOR_KVM to suppress/override the exports. Note, the set of symbols to restrict to KVM was generated by manual search and audit; any "misses" are due to human error, not some grand plan. Signed-off-by: Sean Christopherson Signed-off-by: Dave Hansen Acked-by: Kai Huang Tested-by: Kai Huang Link: https://patch.msgid.link/20251112173944.1380633-5-seanjc%40google.com

x86/nmi: Improve NMI duration console printouts

2025-04-01T20:26:38Z

Convert the last remaining printk() in nmi.c to pr_info(). Along with it, use timespec macros to calculate the NMI handler duration. Signed-off-by: Sohil Mehta Signed-off-by: Ingo Molnar Reviewed-by: Kai Huang Acked-by: Peter Zijlstra (Intel) Reviewed-by: Nikolay Borisov Link: https://lore.kernel.org/r/20250327234629.3953536-10-sohil.mehta@intel.com

x86/nmi: Improve and relocate NMI handler comments

2025-04-01T20:26:16Z

Some of the comments in the default NMI handling code are out of place or inadequate. Move them to the appropriate locations and update them as needed. Move the comment related to CPU-specific NMIs closer to the actual code. Also, add more details about how back-to-back NMIs are detected since that isn't immediately obvious. Opportunistically, replace an #ifdef section in the vicinity with an IS_ENABLED() check to make the code easier to read. Signed-off-by: Sohil Mehta Signed-off-by: Ingo Molnar Acked-by: Kai Huang Acked-by: Peter Zijlstra (Intel) Reviewed-by: Nikolay Borisov Link: https://lore.kernel.org/r/20250327234629.3953536-7-sohil.mehta@intel.com

x86/nmi: Fix comment in unknown_nmi_error()

2025-04-01T20:26:11Z

The comment in unknown_nmi_error() is incorrect and misleading. There is no longer a restriction on having a single Unknown NMI handler. Also, nmi_handle() never used the 'b2b' parameter. The commits that made the comment outdated are: 0d443b70cc92 ("x86/platform: Remove warning message for duplicate NMI handlers") bf9f2ee28d47 ("x86/nmi: Remove the 'b2b' parameter from nmi_handle()") Remove the old comment and update it to reflect the current logic. Signed-off-by: Sohil Mehta Signed-off-by: Ingo Molnar Reviewed-by: Kai Huang Acked-by: Peter Zijlstra (Intel) Reviewed-by: Nikolay Borisov Link: https://lore.kernel.org/r/20250327234629.3953536-6-sohil.mehta@intel.com

x86/nmi: Remove export of local_touch_nmi()

2025-04-01T20:26:06Z

Commit: feb6cd6a0f9f ("thermal/intel_powerclamp: stop sched tick in forced idle") got rid of the last exported user of local_touch_nmi() a while back. Remove the unnecessary export. Signed-off-by: Sohil Mehta Signed-off-by: Ingo Molnar Reviewed-by: Kai Huang Acked-by: Peter Zijlstra (Intel) Reviewed-by: Nikolay Borisov Link: https://lore.kernel.org/r/20250327234629.3953536-5-sohil.mehta@intel.com

x86/nmi: Use a macro to initialize NMI descriptors

2025-04-01T20:26:01Z

The NMI descriptors for each NMI type are stored in an array. However, they are currently initialized using raw numbers, which makes it difficult to understand the code. Introduce a macro to initialize the NMI descriptors using the NMI type enum values to make the code more readable. No functional change intended. Signed-off-by: Sohil Mehta Signed-off-by: Ingo Molnar Reviewed-by: Kai Huang Acked-by: Peter Zijlstra (Intel) Reviewed-by: Nikolay Borisov Link: https://lore.kernel.org/r/20250327234629.3953536-4-sohil.mehta@intel.com

x86/nmi: Consolidate NMI panic variables

2025-04-01T20:25:56Z

Commit: c305a4e98378 ("x86: Move sysctls into arch/x86") recently moved the sysctl handling of panic_on_unrecovered_nmi and panic_on_io_nmi to x86-specific code. These variables no longer need to be declared in the generic header file. Relocate the variable definitions and declarations closer to where they are used. This makes all the NMI panic options consistent and easier to track. [ mingo: Fixed up the SHA1 of the commit reference. ] Signed-off-by: Sohil Mehta Signed-off-by: Ingo Molnar Reviewed-by: Kai Huang Acked-by: Peter Zijlstra (Intel) Reviewed-by: Nikolay Borisov Cc: Joel Granados Link: https://lore.kernel.org/r/20250327234629.3953536-3-sohil.mehta@intel.com

x86/nmi: Add an emergency handler in nmi_desc & use it in nmi_shootdown_cpus()

2025-02-25T13:38:43Z

Depending on the type of panics, it was found that the __register_nmi_handler() function can be called in NMI context from nmi_shootdown_cpus() leading to a lockdep splat: WARNING: inconsistent lock state inconsistent {INITIAL USE} -> {IN-NMI} usage. lock(&nmi_desc[0].lock); lock(&nmi_desc[0].lock); Call Trace: _raw_spin_lock_irqsave __register_nmi_handler nmi_shootdown_cpus kdump_nmi_shootdown_cpus native_machine_crash_shutdown __crash_kexec In this particular case, the following panic message was printed before: Kernel panic - not syncing: Fatal hardware error! This message seemed to be given out from __ghes_panic() running in NMI context. The __register_nmi_handler() function which takes the nmi_desc lock with irq disabled shouldn't be called from NMI context as this can lead to deadlock. The nmi_shootdown_cpus() function can only be invoked once. After the first invocation, all other CPUs should be stuck in the newly added crash_nmi_callback() and cannot respond to a second NMI. Fix it by adding a new emergency NMI handler to the nmi_desc structure and provide a new set_emergency_nmi_handler() helper to set crash_nmi_callback() in any context. The new emergency handler will preempt other handlers in the linked list. That will eliminate the need to take any lock and serve the panic in NMI use case. Signed-off-by: Waiman Long Signed-off-by: Ingo Molnar Acked-by: Rik van Riel Cc: Thomas Gleixner Link: https://lore.kernel.org/r/20250206191844.131700-1-longman@redhat.com

x86/nmi: Upgrade NMI backtrace stall checks & messages

2024-03-26T09:07:59Z

The commit to improve NMI stall debuggability: 344da544f177 ("x86/nmi: Print reasons why backtrace NMIs are ignored") ... has shown value, but widespread use has also identified a few opportunities for improvement. The systems have (as usual) shown far more creativity than that commit's author, demonstrating yet again that failing CPUs can do whatever they want. In addition, the current message format is less friendly than one might like to those attempting to use these messages to identify failing CPUs. Therefore, separately flag CPUs that, during the full time that the stack-backtrace request was waiting, were always in an NMI handler, were never in an NMI handler, or exited one NMI handler. Also, split the message identifying the CPU and the time since that CPU's last NMI-related activity so that a single line identifies the CPU without any other variable information, greatly reducing the processing overhead required to identify repeat-offender CPUs. Co-developed-by: Breno Leitao Signed-off-by: Breno Leitao Signed-off-by: Paul E. McKenney Signed-off-by: Ingo Molnar Cc: Linus Torvalds Link: https://lore.kernel.org/r/ab4d70c8-c874-42dc-b206-643018922393@paulmck-laptop

Merge tag 'x86-cleanups-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2024-03-12T02:37:56Z

Pull x86 cleanups from Ingo Molnar: "Misc cleanups, including a large series from Thomas Gleixner to cure sparse warnings" * tag 'x86-cleanups-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/nmi: Drop unused declaration of proc_nmi_enabled() x86/callthunks: Use EXPORT_PER_CPU_SYMBOL_GPL() for per CPU variables x86/cpu: Provide a declaration for itlb_multihit_kvm_mitigation x86/cpu: Use EXPORT_PER_CPU_SYMBOL_GPL() for x86_spec_ctrl_current x86/uaccess: Add missing __force to casts in __access_ok() and valid_user_address() x86/percpu: Cure per CPU madness on UP smp: Consolidate smp_prepare_boot_cpu() x86/msr: Add missing __percpu annotations x86/msr: Prepare for including into perf/x86/amd/uncore: Fix __percpu annotation x86/nmi: Remove an unnecessary IS_ENABLED(CONFIG_SMP) x86/apm_32: Remove dead function apm_get_battery_status() x86/insn-eval: Fix function param name in get_eff_addr_sib()