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perf/x86/ibs: Fix race with IBS_STARTING state

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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>
This commit is contained in:
Peter Zijlstra 2016-03-16 23:55:21 +01:00 committed by Ingo Molnar
parent 0158b83f75
commit 5a50f52917
1 changed files with 29 additions and 3 deletions
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32
arch/x86/events/amd/ibs.c
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@ -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);