--- /dev/null
+/*
+ * 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/nmi.h>
+#include <linux/debugfs.h>
+#include <linux/delay.h>
+#include <linux/hardirq.h>
+#include <linux/slab.h>
+#include <linux/export.h>
+
+#if defined(CONFIG_EDAC)
+#include <linux/edac.h>
+#endif
+
+#include <linux/atomic.h>
+#include <asm/traps.h>
+#include <asm/mach_traps.h>
+#include <asm/nmi.h>
+#include <asm/x86_init.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/nmi.h>
+
+struct nmi_desc {
+ spinlock_t lock;
+ struct list_head head;
+};
+
+static struct nmi_desc nmi_desc[NMI_MAX] =
+{
+ {
+ .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[0].lock),
+ .head = LIST_HEAD_INIT(nmi_desc[0].head),
+ },
+ {
+ .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[1].lock),
+ .head = LIST_HEAD_INIT(nmi_desc[1].head),
+ },
+ {
+ .lock = __SPIN_LOCK_UNLOCKED(&nmi_desc[2].lock),
+ .head = LIST_HEAD_INIT(nmi_desc[2].head),
+ },
+ {
+ .lock = __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;
+};
+
+static DEFINE_PER_CPU(struct nmi_stats, nmi_stats);
+
+static int ignore_nmis;
+
+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_max_handler(struct irq_work *w)
+{
+ struct nmiaction *a = container_of(w, struct nmiaction, irq_work);
+ int remainder_ns, decimal_msecs;
+ u64 whole_msecs = ACCESS_ONCE(a->max_duration);
+
+ remainder_ns = do_div(whole_msecs, (1000 * 1000));
+ decimal_msecs = remainder_ns / 1000;
+
+ printk_ratelimited(KERN_INFO
+ "INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",
+ a->handler, whole_msecs, decimal_msecs);
+}
+
+static int nmi_handle(unsigned int type, struct pt_regs *regs, bool b2b)
+{
+ 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);
+
+ if (delta < nmi_longest_ns || delta < a->max_duration)
+ continue;
+
+ a->max_duration = delta;
+ irq_work_queue(&a->irq_work);
+ }
+
+ 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 (!action->handler)
+ return -EINVAL;
+
+ init_irq_work(&action->irq_work, nmi_max_handler);
+
+ spin_lock_irqsave(&desc->lock, flags);
+
+ /*
+ * most handlers of type NMI_UNKNOWN never return because
+ * they just assume the NMI is theirs. Just a sanity check
+ * to manage expectations
+ */
+ WARN_ON_ONCE(type == NMI_UNKNOWN && !list_empty(&desc->head));
+ 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);
+
+ 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;
+ unsigned long flags;
+
+ 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);
+ break;
+ }
+ }
+
+ spin_unlock_irqrestore(&desc->lock, flags);
+ synchronize_rcu();
+}
+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, false))
+ return;
+
+ pr_emerg("NMI: PCI system error (SERR) for reason %02x on CPU %d.\n",
+ reason, smp_processor_id());
+
+ /*
+ * On some machines, PCI SERR line is used to report memory
+ * errors. EDAC makes use of it.
+ */
+#if defined(CONFIG_EDAC)
+ if (edac_handler_set()) {
+ edac_atomic_assert_error();
+ return;
+ }
+#endif
+
+ if (panic_on_unrecovered_nmi)
+ panic("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, false))
+ 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)
+ panic("NMI IOCK error: Not continuing");
+
+ /* 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, false);
+ 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());
+
+ pr_emerg("Do you have a strange power saving mode enabled?\n");
+ if (unknown_nmi_panic || panic_on_unrecovered_nmi)
+ panic("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 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);
+
+ handled = nmi_handle(NMI_LOCAL, regs, b2b);
+ __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);
+ return;
+ }
+
+ /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
+ raw_spin_lock(&nmi_reason_lock);
+ 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);
+ return;
+ }
+ 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 descibed above). When the next NMI gets
+ * processed, it will be flagged by perf as handled, but
+ * noone 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);
+}
+NOKPROBE_SYMBOL(default_do_nmi);
+
+/*
+ * NMIs can hit breakpoints which will cause it to lose its
+ * NMI context with the CPU when the breakpoint does an iret.
+ */
+#ifdef CONFIG_X86_32
+/*
+ * For i386, NMIs use the same stack as the kernel, and we can
+ * add a workaround to the iret problem in C (preventing nested
+ * NMIs if an NMI takes a trap). Simply have 3 states the NMI
+ * can be in:
+ *
+ * 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 hits a breakpoint that 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);
+
+#define nmi_nesting_preprocess(regs) \
+ do { \
+ 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()); \
+ } while (0); \
+ nmi_restart:
+
+#define nmi_nesting_postprocess() \
+ do { \
+ if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) \
+ write_cr2(this_cpu_read(nmi_cr2)); \
+ if (this_cpu_dec_return(nmi_state)) \
+ goto nmi_restart; \
+ } while (0)
+#else /* x86_64 */
+/*
+ * In x86_64 things are a bit more difficult. This has the same problem
+ * where an NMI hitting a breakpoint that calls iret will remove the
+ * NMI context, allowing a nested NMI to enter. What makes this more
+ * difficult is that both NMIs and breakpoints have their own stack.
+ * When a new NMI or breakpoint is executed, the stack is set to a fixed
+ * point. If an NMI is nested, it will have its stack set at that same
+ * fixed address that the first NMI had, and will start corrupting the
+ * stack. This is handled in entry_64.S, but the same problem exists with
+ * the breakpoint stack.
+ *
+ * If a breakpoint is being processed, and the debug stack is being used,
+ * if an NMI comes in and also hits a breakpoint, the stack pointer
+ * will be set to the same fixed address as the breakpoint that was
+ * interrupted, causing that stack to be corrupted. To handle this case,
+ * check if the stack that was interrupted is the debug stack, and if
+ * so, change the IDT so that new breakpoints will use the current stack
+ * and not switch to the fixed address. On return of the NMI, switch back
+ * to the original IDT.
+ */
+static DEFINE_PER_CPU(int, update_debug_stack);
+
+static inline void nmi_nesting_preprocess(struct pt_regs *regs)
+{
+ /*
+ * If we interrupted a breakpoint, it is possible that
+ * the nmi handler will have breakpoints too. We need to
+ * change the IDT such that breakpoints that happen here
+ * continue to use the NMI stack.
+ */
+ if (unlikely(is_debug_stack(regs->sp))) {
+ debug_stack_set_zero();
+ this_cpu_write(update_debug_stack, 1);
+ }
+}
+
+static inline void nmi_nesting_postprocess(void)
+{
+ if (unlikely(this_cpu_read(update_debug_stack))) {
+ debug_stack_reset();
+ this_cpu_write(update_debug_stack, 0);
+ }
+}
+#endif
+
+dotraplinkage notrace void
+do_nmi(struct pt_regs *regs, long error_code)
+{
+ nmi_nesting_preprocess(regs);
+
+ nmi_enter();
+
+ inc_irq_stat(__nmi_count);
+
+ if (!ignore_nmis)
+ default_do_nmi(regs);
+
+ nmi_exit();
+
+ /* On i386, may loop back to preprocess */
+ nmi_nesting_postprocess();
+}
+NOKPROBE_SYMBOL(do_nmi);
+
+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);
Code Review / kvmfornfv.git / blobdiff