1 files changed, 662 insertions, 0 deletions

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
new file mode 100644
index 000000000..4766b6bed
--- /dev/null
+++ b/arch/x86/kernel/nmi.c
@@ -0,0 +1,662 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ *  Copyright (C) 2000, 2001, 2002 Andi Kleen, SuSE Labs
+ *  Copyright (C) 2011	Don Zickus Red Hat, Inc.
+ *
+ *  Pentium III FXSR, SSE support
+ *	Gareth Hughes <gareth@valinux.com>, May 2000
+ */
+
+/*
+ * Handle hardware traps and faults.
+ */
+#include <linux/spinlock.h>
+#include <linux/kprobes.h>
+#include <linux/kdebug.h>
+#include <linux/sched/debug.h>
+#include <linux/nmi.h>
+#include <linux/debugfs.h>
+#include <linux/delay.h>
+#include <linux/hardirq.h>
+#include <linux/ratelimit.h>
+#include <linux/slab.h>
+#include <linux/export.h>
+#include <linux/atomic.h>
+#include <linux/sched/clock.h>
+
+#include <asm/cpu_entry_area.h>
+#include <asm/traps.h>
+#include <asm/mach_traps.h>
+#include <asm/nmi.h>
+#include <asm/x86_init.h>
+#include <asm/reboot.h>
+#include <asm/cache.h>
+#include <asm/nospec-branch.h>
+#include <asm/sev.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/nmi.h>
+
+struct nmi_desc {
+	raw_spinlock_t lock;
+	struct list_head head;
+};
+
+static struct nmi_desc nmi_desc[NMI_MAX] = 
+{
+	{
+		.lock = __RAW_SPIN_LOCK_UNLOCKED(&nmi_desc[0].lock),
+		.head = LIST_HEAD_INIT(nmi_desc[0].head),
+	},
+	{
+		.lock = __RAW_SPIN_LOCK_UNLOCKED(&nmi_desc[1].lock),
+		.head = LIST_HEAD_INIT(nmi_desc[1].head),
+	},
+	{
+		.lock = __RAW_SPIN_LOCK_UNLOCKED(&nmi_desc[2].lock),
+		.head = LIST_HEAD_INIT(nmi_desc[2].head),
+	},
+	{
+		.lock = __RAW_SPIN_LOCK_UNLOCKED(&nmi_desc[3].lock),
+		.head = LIST_HEAD_INIT(nmi_desc[3].head),
+	},
+
+};
+
+struct nmi_stats {
+	unsigned int normal;
+	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);
+
+static int ignore_nmis __read_mostly;
+
+int unknown_nmi_panic;
+/*
+ * Prevent NMI reason port (0x61) being accessed simultaneously, can
+ * only be used in NMI handler.
+ */
+static DEFINE_RAW_SPINLOCK(nmi_reason_lock);
+
+static int __init setup_unknown_nmi_panic(char *str)
+{
+	unknown_nmi_panic = 1;
+	return 1;
+}
+__setup("unknown_nmi_panic", setup_unknown_nmi_panic);
+
+#define nmi_to_desc(type) (&nmi_desc[type])
+
+static u64 nmi_longest_ns = 1 * NSEC_PER_MSEC;
+
+static int __init nmi_warning_debugfs(void)
+{
+	debugfs_create_u64("nmi_longest_ns", 0644,
+			arch_debugfs_dir, &nmi_longest_ns);
+	return 0;
+}
+fs_initcall(nmi_warning_debugfs);
+
+static void nmi_check_duration(struct nmiaction *action, u64 duration)
+{
+	int remainder_ns, decimal_msecs;
+
+	if (duration < nmi_longest_ns || duration < action->max_duration)
+		return;
+
+	action->max_duration = duration;
+
+	remainder_ns = do_div(duration, (1000 * 1000));
+	decimal_msecs = remainder_ns / 1000;
+
+	printk_ratelimited(KERN_INFO
+		"INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",
+		action->handler, duration, decimal_msecs);
+}
+
+static int nmi_handle(unsigned int type, struct pt_regs *regs)
+{
+	struct nmi_desc *desc = nmi_to_desc(type);
+	struct nmiaction *a;
+	int handled=0;
+
+	rcu_read_lock();
+
+	/*
+	 * NMIs are edge-triggered, which means if you have enough
+	 * of them concurrently, you can lose some because only one
+	 * can be latched at any given time.  Walk the whole list
+	 * to handle those situations.
+	 */
+	list_for_each_entry_rcu(a, &desc->head, list) {
+		int thishandled;
+		u64 delta;
+
+		delta = sched_clock();
+		thishandled = a->handler(type, regs);
+		handled += thishandled;
+		delta = sched_clock() - delta;
+		trace_nmi_handler(a->handler, (int)delta, thishandled);
+
+		nmi_check_duration(a, delta);
+	}
+
+	rcu_read_unlock();
+
+	/* return total number of NMI events handled */
+	return handled;
+}
+NOKPROBE_SYMBOL(nmi_handle);
+
+int __register_nmi_handler(unsigned int type, struct nmiaction *action)
+{
+	struct nmi_desc *desc = nmi_to_desc(type);
+	unsigned long flags;
+
+	if (WARN_ON_ONCE(!action->handler || !list_empty(&action->list)))
+		return -EINVAL;
+
+	raw_spin_lock_irqsave(&desc->lock, flags);
+
+	/*
+	 * Indicate if there are multiple registrations on the
+	 * internal NMI handler call chains (SERR and IO_CHECK).
+	 */
+	WARN_ON_ONCE(type == NMI_SERR && !list_empty(&desc->head));
+	WARN_ON_ONCE(type == NMI_IO_CHECK && !list_empty(&desc->head));
+
+	/*
+	 * some handlers need to be executed first otherwise a fake
+	 * event confuses some handlers (kdump uses this flag)
+	 */
+	if (action->flags & NMI_FLAG_FIRST)
+		list_add_rcu(&action->list, &desc->head);
+	else
+		list_add_tail_rcu(&action->list, &desc->head);
+
+	raw_spin_unlock_irqrestore(&desc->lock, flags);
+	return 0;
+}
+EXPORT_SYMBOL(__register_nmi_handler);
+
+void unregister_nmi_handler(unsigned int type, const char *name)
+{
+	struct nmi_desc *desc = nmi_to_desc(type);
+	struct nmiaction *n, *found = NULL;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&desc->lock, flags);
+
+	list_for_each_entry_rcu(n, &desc->head, list) {
+		/*
+		 * the name passed in to describe the nmi handler
+		 * is used as the lookup key
+		 */
+		if (!strcmp(n->name, name)) {
+			WARN(in_nmi(),
+				"Trying to free NMI (%s) from NMI context!\n", n->name);
+			list_del_rcu(&n->list);
+			found = n;
+			break;
+		}
+	}
+
+	raw_spin_unlock_irqrestore(&desc->lock, flags);
+	if (found) {
+		synchronize_rcu();
+		INIT_LIST_HEAD(&found->list);
+	}
+}
+EXPORT_SYMBOL_GPL(unregister_nmi_handler);
+
+static void
+pci_serr_error(unsigned char reason, struct pt_regs *regs)
+{
+	/* check to see if anyone registered against these types of errors */
+	if (nmi_handle(NMI_SERR, regs))
+		return;
+
+	pr_emerg("NMI: PCI system error (SERR) for reason %02x on CPU %d.\n",
+		 reason, smp_processor_id());
+
+	if (panic_on_unrecovered_nmi)
+		nmi_panic(regs, "NMI: Not continuing");
+
+	pr_emerg("Dazed and confused, but trying to continue\n");
+
+	/* Clear and disable the PCI SERR error line. */
+	reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_SERR;
+	outb(reason, NMI_REASON_PORT);
+}
+NOKPROBE_SYMBOL(pci_serr_error);
+
+static void
+io_check_error(unsigned char reason, struct pt_regs *regs)
+{
+	unsigned long i;
+
+	/* check to see if anyone registered against these types of errors */
+	if (nmi_handle(NMI_IO_CHECK, regs))
+		return;
+
+	pr_emerg(
+	"NMI: IOCK error (debug interrupt?) for reason %02x on CPU %d.\n",
+		 reason, smp_processor_id());
+	show_regs(regs);
+
+	if (panic_on_io_nmi) {
+		nmi_panic(regs, "NMI IOCK error: Not continuing");
+
+		/*
+		 * If we end up here, it means we have received an NMI while
+		 * processing panic(). Simply return without delaying and
+		 * re-enabling NMIs.
+		 */
+		return;
+	}
+
+	/* Re-enable the IOCK line, wait for a few seconds */
+	reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_IOCHK;
+	outb(reason, NMI_REASON_PORT);
+
+	i = 20000;
+	while (--i) {
+		touch_nmi_watchdog();
+		udelay(100);
+	}
+
+	reason &= ~NMI_REASON_CLEAR_IOCHK;
+	outb(reason, NMI_REASON_PORT);
+}
+NOKPROBE_SYMBOL(io_check_error);
+
+static void
+unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
+{
+	int handled;
+
+	/*
+	 * Use 'false' as back-to-back NMIs are dealt with one level up.
+	 * Of course this makes having multiple 'unknown' handlers useless
+	 * as only the first one is ever run (unless it can actually determine
+	 * if it caused the NMI)
+	 */
+	handled = nmi_handle(NMI_UNKNOWN, regs);
+	if (handled) {
+		__this_cpu_add(nmi_stats.unknown, handled);
+		return;
+	}
+
+	__this_cpu_add(nmi_stats.unknown, 1);
+
+	pr_emerg("Uhhuh. NMI received for unknown reason %02x on CPU %d.\n",
+		 reason, smp_processor_id());
+
+	if (unknown_nmi_panic || panic_on_unrecovered_nmi)
+		nmi_panic(regs, "NMI: Not continuing");
+
+	pr_emerg("Dazed and confused, but trying to continue\n");
+}
+NOKPROBE_SYMBOL(unknown_nmi_error);
+
+static DEFINE_PER_CPU(bool, swallow_nmi);
+static DEFINE_PER_CPU(unsigned long, last_nmi_rip);
+
+static noinstr void default_do_nmi(struct pt_regs *regs)
+{
+	unsigned char reason = 0;
+	int handled;
+	bool b2b = false;
+
+	/*
+	 * CPU-specific NMI must be processed before non-CPU-specific
+	 * NMI, otherwise we may lose it, because the CPU-specific
+	 * NMI can not be detected/processed on other CPUs.
+	 */
+
+	/*
+	 * Back-to-back NMIs are interesting because they can either
+	 * be two NMI or more than two NMIs (any thing over two is dropped
+	 * due to NMI being edge-triggered).  If this is the second half
+	 * of the back-to-back NMI, assume we dropped things and process
+	 * more handlers.  Otherwise reset the 'swallow' NMI behaviour
+	 */
+	if (regs->ip == __this_cpu_read(last_nmi_rip))
+		b2b = true;
+	else
+		__this_cpu_write(swallow_nmi, false);
+
+	__this_cpu_write(last_nmi_rip, regs->ip);
+
+	instrumentation_begin();
+
+	handled = nmi_handle(NMI_LOCAL, regs);
+	__this_cpu_add(nmi_stats.normal, handled);
+	if (handled) {
+		/*
+		 * There are cases when a NMI handler handles multiple
+		 * events in the current NMI.  One of these events may
+		 * be queued for in the next NMI.  Because the event is
+		 * already handled, the next NMI will result in an unknown
+		 * NMI.  Instead lets flag this for a potential NMI to
+		 * swallow.
+		 */
+		if (handled > 1)
+			__this_cpu_write(swallow_nmi, true);
+		goto out;
+	}
+
+	/*
+	 * Non-CPU-specific NMI: NMI sources can be processed on any CPU.
+	 *
+	 * Another CPU may be processing panic routines while holding
+	 * nmi_reason_lock. Check if the CPU issued the IPI for crash dumping,
+	 * and if so, call its callback directly.  If there is no CPU preparing
+	 * crash dump, we simply loop here.
+	 */
+	while (!raw_spin_trylock(&nmi_reason_lock)) {
+		run_crash_ipi_callback(regs);
+		cpu_relax();
+	}
+
+	reason = x86_platform.get_nmi_reason();
+
+	if (reason & NMI_REASON_MASK) {
+		if (reason & NMI_REASON_SERR)
+			pci_serr_error(reason, regs);
+		else if (reason & NMI_REASON_IOCHK)
+			io_check_error(reason, regs);
+#ifdef CONFIG_X86_32
+		/*
+		 * Reassert NMI in case it became active
+		 * meanwhile as it's edge-triggered:
+		 */
+		reassert_nmi();
+#endif
+		__this_cpu_add(nmi_stats.external, 1);
+		raw_spin_unlock(&nmi_reason_lock);
+		goto out;
+	}
+	raw_spin_unlock(&nmi_reason_lock);
+
+	/*
+	 * Only one NMI can be latched at a time.  To handle
+	 * this we may process multiple nmi handlers at once to
+	 * cover the case where an NMI is dropped.  The downside
+	 * to this approach is we may process an NMI prematurely,
+	 * while its real NMI is sitting latched.  This will cause
+	 * an unknown NMI on the next run of the NMI processing.
+	 *
+	 * We tried to flag that condition above, by setting the
+	 * swallow_nmi flag when we process more than one event.
+	 * This condition is also only present on the second half
+	 * of a back-to-back NMI, so we flag that condition too.
+	 *
+	 * If both are true, we assume we already processed this
+	 * NMI previously and we swallow it.  Otherwise we reset
+	 * the logic.
+	 *
+	 * There are scenarios where we may accidentally swallow
+	 * a 'real' unknown NMI.  For example, while processing
+	 * a perf NMI another perf NMI comes in along with a
+	 * 'real' unknown NMI.  These two NMIs get combined into
+	 * one (as described above).  When the next NMI gets
+	 * processed, it will be flagged by perf as handled, but
+	 * no one will know that there was a 'real' unknown NMI sent
+	 * also.  As a result it gets swallowed.  Or if the first
+	 * perf NMI returns two events handled then the second
+	 * NMI will get eaten by the logic below, again losing a
+	 * 'real' unknown NMI.  But this is the best we can do
+	 * for now.
+	 */
+	if (b2b && __this_cpu_read(swallow_nmi))
+		__this_cpu_add(nmi_stats.swallow, 1);
+	else
+		unknown_nmi_error(reason, regs);
+
+out:
+	instrumentation_end();
+}
+
+/*
+ * NMIs can page fault or hit breakpoints which will cause it to lose
+ * its NMI context with the CPU when the breakpoint or page fault does an IRET.
+ *
+ * As a result, NMIs can nest if NMIs get unmasked due an IRET during
+ * NMI processing.  On x86_64, the asm glue protects us from nested NMIs
+ * if the outer NMI came from kernel mode, but we can still nest if the
+ * outer NMI came from user mode.
+ *
+ * To handle these nested NMIs, we have three states:
+ *
+ *  1) not running
+ *  2) executing
+ *  3) latched
+ *
+ * When no NMI is in progress, it is in the "not running" state.
+ * When an NMI comes in, it goes into the "executing" state.
+ * Normally, if another NMI is triggered, it does not interrupt
+ * the running NMI and the HW will simply latch it so that when
+ * the first NMI finishes, it will restart the second NMI.
+ * (Note, the latch is binary, thus multiple NMIs triggering,
+ *  when one is running, are ignored. Only one NMI is restarted.)
+ *
+ * If an NMI executes an iret, another NMI can preempt it. We do not
+ * want to allow this new NMI to run, but we want to execute it when the
+ * first one finishes.  We set the state to "latched", and the exit of
+ * the first NMI will perform a dec_return, if the result is zero
+ * (NOT_RUNNING), then it will simply exit the NMI handler. If not, the
+ * dec_return would have set the state to NMI_EXECUTING (what we want it
+ * to be when we are running). In this case, we simply jump back to
+ * rerun the NMI handler again, and restart the 'latched' NMI.
+ *
+ * No trap (breakpoint or page fault) should be hit before nmi_restart,
+ * thus there is no race between the first check of state for NOT_RUNNING
+ * and setting it to NMI_EXECUTING. The HW will prevent nested NMIs
+ * at this point.
+ *
+ * In case the NMI takes a page fault, we need to save off the CR2
+ * because the NMI could have preempted another page fault and corrupt
+ * the CR2 that is about to be read. As nested NMIs must be restarted
+ * and they can not take breakpoints or page faults, the update of the
+ * CR2 must be done before converting the nmi state back to NOT_RUNNING.
+ * Otherwise, there would be a race of another nested NMI coming in
+ * after setting state to NOT_RUNNING but before updating the nmi_cr2.
+ */
+enum nmi_states {
+	NMI_NOT_RUNNING = 0,
+	NMI_EXECUTING,
+	NMI_LATCHED,
+};
+static DEFINE_PER_CPU(enum nmi_states, nmi_state);
+static DEFINE_PER_CPU(unsigned long, nmi_cr2);
+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))
+		raw_atomic_long_inc(&nsp->idt_calls);
+
+	if (IS_ENABLED(CONFIG_SMP) && arch_cpu_is_offline(smp_processor_id()))
+		return;
+
+	if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) {
+		this_cpu_write(nmi_state, NMI_LATCHED);
+		return;
+	}
+	this_cpu_write(nmi_state, NMI_EXECUTING);
+	this_cpu_write(nmi_cr2, read_cr2());
+
+nmi_restart:
+	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);
+	}
+
+	/*
+	 * Needs to happen before DR7 is accessed, because the hypervisor can
+	 * intercept DR7 reads/writes, turning those into #VC exceptions.
+	 */
+	sev_es_ist_enter(regs);
+
+	this_cpu_write(nmi_dr7, local_db_save());
+
+	irq_state = irqentry_nmi_enter(regs);
+
+	inc_irq_stat(__nmi_count);
+
+	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);
+
+	local_db_restore(this_cpu_read(nmi_dr7));
+
+	sev_es_ist_exit();
+
+	if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))
+		write_cr2(this_cpu_read(nmi_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);
+	}
+	if (this_cpu_dec_return(nmi_state))
+		goto nmi_restart;
+
+	if (user_mode(regs))
+		mds_user_clear_cpu_buffers();
+}
+
+#if IS_ENABLED(CONFIG_KVM_INTEL)
+DEFINE_IDTENTRY_RAW(exc_nmi_kvm_vmx)
+{
+	exc_nmi(regs);
+}
+#if IS_MODULE(CONFIG_KVM_INTEL)
+EXPORT_SYMBOL_GPL(asm_exc_nmi_kvm_vmx);
+#endif
+#endif
+
+#ifdef CONFIG_NMI_CHECK_CPU
+
+static char *nmi_check_stall_msg[] = {
+/*									*/
+/* +--------- nsp->idt_seq_snap & 0x1: CPU is in NMI handler.		*/
+/* | +------ cpu_is_offline(cpu)					*/
+/* | | +--- nsp->idt_calls_snap != atomic_long_read(&nsp->idt_calls):	*/
+/* | | |	NMI handler has been invoked.				*/
+/* | | |								*/
+/* V V V								*/
+/* 0 0 0 */ "NMIs are not reaching exc_nmi() handler",
+/* 0 0 1 */ "exc_nmi() handler is ignoring NMIs",
+/* 0 1 0 */ "CPU is offline and NMIs are not reaching exc_nmi() handler",
+/* 0 1 1 */ "CPU is offline and exc_nmi() handler is legitimately ignoring NMIs",
+/* 1 0 0 */ "CPU is in exc_nmi() handler and no further NMIs are reaching handler",
+/* 1 0 1 */ "CPU is in exc_nmi() handler which is legitimately ignoring NMIs",
+/* 1 1 0 */ "CPU is offline in exc_nmi() handler and no more NMIs are reaching exc_nmi() handler",
+/* 1 1 1 */ "CPU is offline in exc_nmi() handler which is legitimately ignoring NMIs",
+};
+
+void nmi_backtrace_stall_snap(const struct cpumask *btp)
+{
+	int cpu;
+	struct nmi_stats *nsp;
+
+	for_each_cpu(cpu, btp) {
+		nsp = per_cpu_ptr(&nmi_stats, cpu);
+		nsp->idt_seq_snap = READ_ONCE(nsp->idt_seq);
+		nsp->idt_nmi_seq_snap = READ_ONCE(nsp->idt_nmi_seq);
+		nsp->idt_ignored_snap = READ_ONCE(nsp->idt_ignored);
+		nsp->idt_calls_snap = atomic_long_read(&nsp->idt_calls);
+	}
+}
+
+void nmi_backtrace_stall_check(const struct cpumask *btp)
+{
+	int cpu;
+	int idx;
+	unsigned long nmi_seq;
+	unsigned long j = jiffies;
+	char *modp;
+	char *msgp;
+	char *msghp;
+	struct nmi_stats *nsp;
+
+	for_each_cpu(cpu, btp) {
+		nsp = per_cpu_ptr(&nmi_stats, cpu);
+		modp = "";
+		msghp = "";
+		nmi_seq = READ_ONCE(nsp->idt_nmi_seq);
+		if (nsp->idt_nmi_seq_snap + 1 == nmi_seq && (nmi_seq & 0x1)) {
+			msgp = "CPU entered NMI handler function, but has not exited";
+		} else if ((nsp->idt_nmi_seq_snap & 0x1) != (nmi_seq & 0x1)) {
+			msgp = "CPU is handling NMIs";
+		} else {
+			idx = ((nsp->idt_seq_snap & 0x1) << 2) |
+			      (cpu_is_offline(cpu) << 1) |
+			      (nsp->idt_calls_snap != atomic_long_read(&nsp->idt_calls));
+			msgp = nmi_check_stall_msg[idx];
+			if (nsp->idt_ignored_snap != READ_ONCE(nsp->idt_ignored) && (idx & 0x1))
+				modp = ", but OK because ignore_nmis was set";
+			if (nmi_seq & ~0x1)
+				msghp = " (CPU currently in NMI handler function)";
+			else if (nsp->idt_nmi_seq_snap + 1 == nmi_seq)
+				msghp = " (CPU exited one NMI handler function)";
+		}
+		pr_alert("%s: CPU %d: %s%s%s, last activity: %lu jiffies ago.\n",
+			 __func__, cpu, msgp, modp, msghp, j - READ_ONCE(nsp->recv_jiffies));
+	}
+}
+
+#endif
+
+void stop_nmi(void)
+{
+	ignore_nmis++;
+}
+
+void restart_nmi(void)
+{
+	ignore_nmis--;
+}
+
+/* reset the back-to-back NMI logic */
+void local_touch_nmi(void)
+{
+	__this_cpu_write(last_nmi_rip, 0);
+}
+EXPORT_SYMBOL_GPL(local_touch_nmi);