[patch 3/3] x86, perf_counter, bts: do not allow kernel BTS tracing.

[markus . t . metzger]

Kernel BTS tracing generates too much data too fast for us to handle,
causing the kernel to hang.

Fail for BTS requests for kernel code.

CC: Peter Zijlstra <a.p.zjilstra@xxxxxxxxx>
Signed-off-by: Markus Metzger <markus.t.metzger@xxxxxxxxx>
---
 arch/x86/kernel/cpu/perf_counter.c |   11 	9 +	2 -	0 !
 1 files changed, 9 insertions(+), 2 deletions(-)

Index: b/arch/x86/kernel/cpu/perf_counter.c
===================================================================
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -984,8 +984,15 @@ static int __hw_perf_counter_init(struct
 	 * Branch tracing:
 	 */
 	if ((attr->config == PERF_COUNT_HW_BRANCH_INSTRUCTIONS) &&
-	    (hwc->sample_period == 1) && !bts_available())
-		return -EOPNOTSUPP;
+	    (hwc->sample_period == 1)) {
+		/* BTS is not supported by this architecture. */
+		if (!bts_available())
+			return -EOPNOTSUPP;
+
+		/* BTS is currently only allowed for user-mode. */
+		if (hwc->config & ARCH_PERFMON_EVENTSEL_OS)
+			return -EOPNOTSUPP;
+	}
 
 	hwc->config |= config;
 

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