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author | Peter Zijlstra <peterz@infradead.org> | 2016-03-17 01:55:21 +0300 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2016-03-21 11:08:15 +0300 |
commit | 5a50f52917011365a4a2c0f1d2cea0990c4465cd (patch) | |
tree | 35a40bdf23e947e83caa3ebb5d3948e3ff72e69c /arch/x86 | |
parent | 0158b83f7508851cda9e62c4b14678c5bd492cb2 (diff) | |
download | linux-5a50f52917011365a4a2c0f1d2cea0990c4465cd.tar.xz |
perf/x86/ibs: Fix race with IBS_STARTING state
While tracing the IBS bits I saw the NMI hitting between clearing
IBS_STARTING and the actual MSR writes to disable the counter.
Since IBS_STARTING was cleared, the handler assumed these were spurious
NMIs and because STOPPING wasn't set yet either, insta-triggered an
"Unknown NMI".
Cure this by clearing IBS_STARTING after disabling the hardware.
Tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86')
-rw-r--r-- | arch/x86/events/amd/ibs.c | 32 |
1 files changed, 29 insertions, 3 deletions
diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c index 7956d29762ef..c43a36d5fd6f 100644 --- a/arch/x86/events/amd/ibs.c +++ b/arch/x86/events/amd/ibs.c @@ -376,7 +376,13 @@ static void perf_ibs_start(struct perf_event *event, int flags) hwc->state = 0; perf_ibs_set_period(perf_ibs, hwc, &period); + /* + * Set STARTED before enabling the hardware, such that + * a subsequent NMI must observe it. Then clear STOPPING + * such that we don't consume NMIs by accident. + */ set_bit(IBS_STARTED, pcpu->state); + clear_bit(IBS_STOPPING, pcpu->state); perf_ibs_enable_event(perf_ibs, hwc, period >> 4); perf_event_update_userpage(event); @@ -390,7 +396,7 @@ static void perf_ibs_stop(struct perf_event *event, int flags) u64 config; int stopping; - stopping = test_and_clear_bit(IBS_STARTED, pcpu->state); + stopping = test_bit(IBS_STARTED, pcpu->state); if (!stopping && (hwc->state & PERF_HES_UPTODATE)) return; @@ -398,8 +404,24 @@ static void perf_ibs_stop(struct perf_event *event, int flags) rdmsrl(hwc->config_base, config); if (stopping) { + /* + * Set STOPPING before disabling the hardware, such that it + * must be visible to NMIs the moment we clear the EN bit, + * at which point we can generate an !VALID sample which + * we need to consume. + */ set_bit(IBS_STOPPING, pcpu->state); perf_ibs_disable_event(perf_ibs, hwc, config); + /* + * Clear STARTED after disabling the hardware; if it were + * cleared before an NMI hitting after the clear but before + * clearing the EN bit might think it a spurious NMI and not + * handle it. + * + * Clearing it after, however, creates the problem of the NMI + * handler seeing STARTED but not having a valid sample. + */ + clear_bit(IBS_STARTED, pcpu->state); WARN_ON_ONCE(hwc->state & PERF_HES_STOPPED); hwc->state |= PERF_HES_STOPPED; } @@ -527,20 +549,24 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs) u64 *buf, *config, period; if (!test_bit(IBS_STARTED, pcpu->state)) { +fail: /* * Catch spurious interrupts after stopping IBS: After * disabling IBS there could be still incoming NMIs * with samples that even have the valid bit cleared. * Mark all this NMIs as handled. */ - return test_and_clear_bit(IBS_STOPPING, pcpu->state) ? 1 : 0; + if (test_and_clear_bit(IBS_STOPPING, pcpu->state)) + return 1; + + return 0; } msr = hwc->config_base; buf = ibs_data.regs; rdmsrl(msr, *buf); if (!(*buf++ & perf_ibs->valid_mask)) - return 0; + goto fail; config = &ibs_data.regs[0]; perf_ibs_event_update(perf_ibs, event, config); |