Commit 1a3ea611 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

x86/nmi: Accumulate NMI-progress evidence in exc_nmi() 



CPUs ignoring NMIs is often a sign of those CPUs going bad, but there
are quite a few other reasons why a CPU might ignore NMIs.  Therefore,
accumulate evidence within exc_nmi() as to what might be preventing a
given CPU from responding to an NMI.

[ paulmck: Apply Peter Zijlstra feedback. ]

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: <x86@kernel.org>
Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1b929c02

arch/x86/kernel/nmi.c

+34 −1
Original line number Diff line number Diff line
@@ -69,6 +69,15 @@ struct nmi_stats { 
	unsigned int unknown;

	unsigned int external;

	unsigned int swallow;

	unsigned long recv_jiffies;

	unsigned long idt_seq;

	unsigned long idt_nmi_seq;

	unsigned long idt_ignored;

	atomic_long_t idt_calls;

	unsigned long idt_seq_snap;

	unsigned long idt_nmi_seq_snap;

	unsigned long idt_ignored_snap;

	long idt_calls_snap;

};



static DEFINE_PER_CPU(struct nmi_stats, nmi_stats);
@@ -479,12 +488,15 @@ static DEFINE_PER_CPU(unsigned long, nmi_dr7); 
DEFINE_IDTENTRY_RAW(exc_nmi)

{

	irqentry_state_t irq_state;

	struct nmi_stats *nsp = this_cpu_ptr(&nmi_stats);



	/*

	 * Re-enable NMIs right here when running as an SEV-ES guest. This might

	 * cause nested NMIs, but those can be handled safely.

	 */

	sev_es_nmi_complete();

	if (IS_ENABLED(CONFIG_NMI_CHECK_CPU))

		arch_atomic_long_inc(&nsp->idt_calls);



	if (IS_ENABLED(CONFIG_SMP) && arch_cpu_is_offline(smp_processor_id()))

		return;
@@ -495,6 +507,11 @@ DEFINE_IDTENTRY_RAW(exc_nmi) 
	}

	this_cpu_write(nmi_state, NMI_EXECUTING);

	this_cpu_write(nmi_cr2, read_cr2());

	if (IS_ENABLED(CONFIG_NMI_CHECK_CPU)) {

		WRITE_ONCE(nsp->idt_seq, nsp->idt_seq + 1);

		WARN_ON_ONCE(!(nsp->idt_seq & 0x1));

		WRITE_ONCE(nsp->recv_jiffies, jiffies);

	}

nmi_restart:



	/*
@@ -509,8 +526,19 @@ DEFINE_IDTENTRY_RAW(exc_nmi) 


	inc_irq_stat(__nmi_count);



	if (!ignore_nmis)

	if (IS_ENABLED(CONFIG_NMI_CHECK_CPU) && ignore_nmis) {

		WRITE_ONCE(nsp->idt_ignored, nsp->idt_ignored + 1);

	} else if (!ignore_nmis) {

		if (IS_ENABLED(CONFIG_NMI_CHECK_CPU)) {

			WRITE_ONCE(nsp->idt_nmi_seq, nsp->idt_nmi_seq + 1);

			WARN_ON_ONCE(!(nsp->idt_nmi_seq & 0x1));

		}

		default_do_nmi(regs);

		if (IS_ENABLED(CONFIG_NMI_CHECK_CPU)) {

			WRITE_ONCE(nsp->idt_nmi_seq, nsp->idt_nmi_seq + 1);

			WARN_ON_ONCE(nsp->idt_nmi_seq & 0x1);

		}

	}



	irqentry_nmi_exit(regs, irq_state);
@@ -525,6 +553,11 @@ DEFINE_IDTENTRY_RAW(exc_nmi) 


	if (user_mode(regs))

		mds_user_clear_cpu_buffers();

	if (IS_ENABLED(CONFIG_NMI_CHECK_CPU)) {

		WRITE_ONCE(nsp->idt_seq, nsp->idt_seq + 1);

		WARN_ON_ONCE(nsp->idt_seq & 0x1);

		WRITE_ONCE(nsp->recv_jiffies, jiffies);

	}

}



#if defined(CONFIG_X86_64) && IS_ENABLED(CONFIG_KVM_INTEL)

lib/Kconfig.debug

+11 −0
Original line number Diff line number Diff line
@@ -1552,6 +1552,17 @@ config TRACE_IRQFLAGS_NMI 
	depends on TRACE_IRQFLAGS

	depends on TRACE_IRQFLAGS_NMI_SUPPORT



config NMI_CHECK_CPU

	bool "Debugging for CPUs failing to respond to backtrace requests"

	depends on DEBUG_KERNEL

	depends on X86

	default n

	help

	  Enables debug prints when a CPU fails to respond to a given

	  backtrace NMI.  These prints provide some reasons why a CPU

	  might legitimately be failing to respond, for example, if it

	  is offline of if ignore_nmis is set.



config DEBUG_IRQFLAGS

	bool "Debug IRQ flag manipulation"

	help