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Commit 5a50f529 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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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: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 0158b83f

arch/x86/events/amd/ibs.c

+29 −3
Original line number Diff line number Diff line
@@ -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);