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Merge tag 'nmi.2023.02.14a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

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Pull x86 NMI diagnostics from Paul McKenney:
 "Add diagnostics to the x86 NMI handler to help detect NMI-handler bugs
  on the one hand and failing hardware on the other"

* tag 'nmi.2023.02.14a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
  x86/nmi: Print reasons why backtrace NMIs are ignored
  x86/nmi: Accumulate NMI-progress evidence in exc_nmi()
This commit is contained in:
Linus Torvalds
2023-02-23 09:28:37 -08:00
parent 192a5e0a19 344da544f1
commit 525445efac
4 changed files with 128 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files
arch/x86/kernel/nmi.c
+107 -1
View File
@@ -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 @@ nmi_restart:
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 @@ nmi_restart:
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)
@@ -537,6 +570,79 @@ DEFINE_IDTENTRY_RAW(exc_nmi_noist)
EXPORT_SYMBOL_GPL(asm_exc_nmi_noist);
#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++;
include/linux/nmi.h
+8
View File
@@ -214,4 +214,12 @@ int proc_watchdog_cpumask(struct ctl_table *, int, void *, size_t *, loff_t *);
#include <asm/nmi.h>
#endif
#ifdef CONFIG_NMI_CHECK_CPU
void nmi_backtrace_stall_snap(const struct cpumask *btp);
void nmi_backtrace_stall_check(const struct cpumask *btp);
#else
static inline void nmi_backtrace_stall_snap(const struct cpumask *btp) {}
static inline void nmi_backtrace_stall_check(const struct cpumask *btp) {}
#endif
#endif
lib/Kconfig.debug
+11
View File
@@ -1562,6 +1562,17 @@ 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
lib/nmi_backtrace.c
+2
View File
@@ -64,6 +64,7 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
if (!cpumask_empty(to_cpumask(backtrace_mask))) {
pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
nmi_backtrace_stall_snap(to_cpumask(backtrace_mask));
raise(to_cpumask(backtrace_mask));
}
@@ -74,6 +75,7 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
mdelay(1);
touch_softlockup_watchdog();
}
nmi_backtrace_stall_check(to_cpumask(backtrace_mask));
/*
* Force flush any remote buffers that might be stuck in IRQ context