[patch 1/4] x86, bts: add selftest for BTS

[Markus Metzger]

Add code to test the branch trace store functionality when a cpu
is initialized.

If an error is detected, a WARN()ing is issued and bts is disabled.


Signed-off-by: Markus Metzger <markus.t.metzger@xxxxxxxxx>
---

Index: gits/arch/x86/kernel/ds.c
===================================================================
--- gits.orig/arch/x86/kernel/ds.c	2009-03-03 17:24:56.000000000 +0100
+++ gits/arch/x86/kernel/ds.c	2009-03-03 17:30:36.000000000 +0100
@@ -926,8 +926,217 @@ static const struct ds_configuration ds_
 	.sizeof_rec[ds_pebs]	= 8 * 18,
 };
 
-static void
-ds_configure(const struct ds_configuration *cfg)
+#ifdef CONFIG_X86_DS_SELFTEST
+static int ds_selftest_bts_consistency(const struct bts_trace *trace)
+{
+	int error = 0;
+
+	if (!trace) {
+		printk(KERN_CONT "failed to access trace...");
+		/* Bail out. Other tests are pointless. */
+		return -1;
+	}
+
+	if (!trace->read) {
+		printk(KERN_CONT "bts read not available...");
+		error = -1;
+	}
+
+	/* Do some sanity checks on the trace configuration. */
+	if (!trace->ds.n) {
+		printk(KERN_CONT "empty bts buffer...");
+		error = -1;
+	}
+	if (!trace->ds.size) {
+		printk(KERN_CONT "bad bts trace setup...");
+		error = -1;
+	}
+	if (trace->ds.end !=
+	    (char *) trace->ds.begin + (trace->ds.n * trace->ds.size)) {
+		printk(KERN_CONT "bad bts buffer setup...");
+		error = -1;
+	}
+	if ((trace->ds.top < trace->ds.begin) ||
+	    (trace->ds.end <= trace->ds.top)) {
+		printk(KERN_CONT "bts top out of bounds...");
+		error = -1;
+	}
+
+	return error;
+}
+
+static int ds_selftest_bts_read(struct bts_tracer *tracer,
+				const struct bts_trace *trace,
+				const void *from, const void *to)
+{
+	const unsigned char *at;
+
+	/* Check a few things which do not belong to this test.
+	 * They should be covered by other tests. */
+	if (!trace)
+		return -1;
+
+	if (!trace->read)
+		return -1;
+
+	if (to < from)
+		return -1;
+
+	if (from < trace->ds.begin)
+		return -1;
+
+	if (trace->ds.end < to)
+		return -1;
+
+	if (!trace->ds.size)
+		return -1;
+
+	/* Now to the test itself. */
+	for (at = from; (void *) at < to; at += trace->ds.size) {
+		struct bts_struct bts;
+		size_t index;
+		int error;
+
+		if (((void *) at - trace->ds.begin) % trace->ds.size) {
+			printk(KERN_CONT
+			       "read from non-integer index...");
+			return -1;
+		}
+		index = ((void *) at - trace->ds.begin) / trace->ds.size;
+
+		memset(&bts, 0, sizeof(bts));
+		error = trace->read(tracer, at, &bts);
+		if (error < 0) {
+			printk(KERN_CONT
+			       "error reading bts trace at [%lu] (0x%p)...",
+			       index, at);
+			return error;
+		}
+
+		switch (bts.qualifier) {
+		case BTS_BRANCH:
+			break;
+		default:
+			printk(KERN_CONT
+			       "unexpected bts entry %llu at [%lu] (0x%p)...",
+			       bts.qualifier, index, at);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+#define DS_SELFTEST_SIZEOF_BUFFER 1021 /* intentionally chose an odd size */
+static int ds_selftest_bts(void)
+{
+	const struct bts_trace *trace;
+	struct bts_tracer *tracer;
+	int error = 0;
+	void *top;
+	unsigned char buffer[DS_SELFTEST_SIZEOF_BUFFER];
+
+	tracer =
+		ds_request_bts(/* task = */ NULL, buffer,
+			       DS_SELFTEST_SIZEOF_BUFFER,
+			       /* ovfl = */ NULL, /* th = */ (size_t)-1,
+			       BTS_KERNEL);
+	if (IS_ERR(tracer)) {
+		error = PTR_ERR(tracer);
+		tracer = NULL;
+
+		printk(KERN_CONT
+		       "initialization failed (err: %d)...", error);
+		goto out;
+	}
+
+	/* The return from the initialization call should already give
+	 * us enough trace. */
+	ds_suspend_bts(tracer);
+
+	/* Let's see if we can access the trace. */
+	trace = ds_read_bts(tracer);
+
+	error = ds_selftest_bts_consistency(trace);
+	if (error < 0)
+		goto out;
+
+	/* If everything went well, we should have a few trace entries. */
+	if (trace->ds.top == trace->ds.begin) {
+		/* It is possible but highly unlikely that we got a
+		 * buffer overflow and end up at exactly the same
+		 * position we started from.
+		 * Let's issue a warning, but continue. */
+		printk(KERN_CONT "no trace/overflow...");
+	}
+
+	/* Let's try to read the trace we collected. */
+	error = ds_selftest_bts_read(tracer, trace,
+				     trace->ds.begin, trace->ds.top);
+	if (error < 0)
+		goto out;
+
+	/* Let's read the trace again. Since we suspended tracing, we should
+	 * get the same result. */
+	top = trace->ds.top;
+
+	trace = ds_read_bts(tracer);
+	error = ds_selftest_bts_consistency(trace);
+	if (error < 0)
+		goto out;
+
+	if (top != trace->ds.top) {
+		printk(KERN_CONT "suspend not working...");
+		error = -1;
+		goto out;
+	}
+
+	/* Let's collect some more trace - see if resume is working. */
+	ds_resume_bts(tracer);
+	ds_suspend_bts(tracer);
+
+	trace = ds_read_bts(tracer);
+
+	error = ds_selftest_bts_consistency(trace);
+	if (error < 0)
+		goto out;
+
+	if (trace->ds.top == top) {
+		/* It is possible but highly unlikely that we got a
+		 * buffer overflow and end up at exactly the same
+		 * position we started from.
+		 * Let's issue a warning and check the full trace. */
+		printk(KERN_CONT
+		       "no resume progress/overflow...");
+
+		error = ds_selftest_bts_read(tracer, trace,
+					     trace->ds.begin, trace->ds.end);
+	} else if (trace->ds.top < top) {
+		/* We had a buffer overflow - the entire buffer should
+		 * contain trace records. */
+		error = ds_selftest_bts_read(tracer, trace,
+					     trace->ds.begin, trace->ds.end);
+	} else {
+		/* It is quite likely that the buffer did not
+		 * overflow. Let's just check the delta trace. */
+		error = ds_selftest_bts_read(tracer, trace,
+					     top, trace->ds.top);
+	}
+	if (error < 0)
+		goto out;
+
+	error = 0;
+
+	/* The final test: release the tracer while tracing is suspended. */
+ out:
+	ds_release_bts(tracer);
+
+	return error;
+}
+#endif /* CONFIG_X86_DS_SELFTEST */
+
+
+static void ds_configure(const struct ds_configuration *cfg)
 {
 	memset(&ds_cfg, 0, sizeof(ds_cfg));
 	ds_cfg = *cfg;
@@ -942,6 +1151,21 @@ ds_configure(const struct ds_configurati
 		printk(KERN_INFO "[ds] pebs not available\n");
 
 	WARN_ON_ONCE(MAX_SIZEOF_DS < (12 * ds_cfg.sizeof_field));
+
+#ifdef CONFIG_X86_DS_SELFTEST
+	if (ds_cfg.ctl[dsf_bts]) {
+		int error;
+
+		printk(KERN_INFO "[ds] bts selftest...");
+		error = ds_selftest_bts();
+		printk(KERN_CONT "%s.\n", (error ? "failed" : "passed"));
+
+		if (error) {
+			WARN(1, "[ds] selftest failed. disabling bts.\n");
+			ds_cfg.ctl[dsf_bts] = 0;
+		}
+	}
+#endif /* CONFIG_X86_DS_SELFTEST */
 }
 
 void __cpuinit ds_init_intel(struct cpuinfo_x86 *c)
Index: gits/arch/x86/Kconfig.debug
===================================================================
--- gits.orig/arch/x86/Kconfig.debug	2009-03-03 17:24:57.000000000 +0100
+++ gits/arch/x86/Kconfig.debug	2009-03-03 17:25:01.000000000 +0100
@@ -176,6 +176,15 @@ config IOMMU_LEAK
 	  Add a simple leak tracer to the IOMMU code. This is useful when you
 	  are debugging a buggy device driver that leaks IOMMU mappings.
 
+config X86_DS_SELFTEST
+    bool "DS selftest"
+    default y
+    depends on DEBUG_KERNEL
+    depends on X86_DS
+	---help---
+	  Perform Debug Store selftests at boot time.
+	  If in doubt, say "N".
+
 config HAVE_MMIOTRACE_SUPPORT
 	def_bool y
 
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