From 7f47d8cc039f8746e0038fe05f1ddcb15a2e27f0 Mon Sep 17 00:00:00 2001
From: Andi Kleen <ak@linux.intel.com>
Date: Tue, 1 Dec 2015 17:00:59 -0800
Subject: x86, tracing, perf: Add trace point for MSR accesses

For debugging low level code interacting with the CPU it is often
useful to trace the MSR read/writes. This gives a concise summary of
PMU and other operations.

perf has an ad-hoc way to do this using trace_printk, but it's
somewhat limited (and also now spews ugly boot messages when enabled)

Instead define real trace points for all MSR accesses.

This adds three new trace points: read_msr and write_msr and rdpmc.

They also report if the access faulted (if *_safe is used)

This allows filtering and triggering on specific MSR values, which
allows various more advanced debugging techniques.

All the values are well defined in the CPU documentation.

The trace can be post processed with
Documentation/trace/postprocess/decode_msr.py to add symbolic MSR
names to the trace.

I only added it to native MSR accesses in C, not paravirtualized or in
entry*.S (which is not too interesting)

Originally the patch kit moved the MSRs out of line.  This uses an
alternative approach recommended by Steven Rostedt of only moving the
trace calls out of line, but open coding the access to the jump label.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
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>
Link: http://lkml.kernel.org/r/1449018060-1742-3-git-send-email-andi@firstfloor.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/lib/msr.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

(limited to 'arch/x86/lib/msr.c')

diff --git a/arch/x86/lib/msr.c b/arch/x86/lib/msr.c
index 43623739c7cf..004c861b1648 100644
--- a/arch/x86/lib/msr.c
+++ b/arch/x86/lib/msr.c
@@ -1,6 +1,8 @@
 #include <linux/module.h>
 #include <linux/preempt.h>
 #include <asm/msr.h>
+#define CREATE_TRACE_POINTS
+#include <asm/msr-trace.h>
 
 struct msr *msrs_alloc(void)
 {
@@ -108,3 +110,27 @@ int msr_clear_bit(u32 msr, u8 bit)
 {
 	return __flip_bit(msr, bit, false);
 }
+
+#ifdef CONFIG_TRACEPOINTS
+void do_trace_write_msr(unsigned msr, u64 val, int failed)
+{
+	trace_write_msr(msr, val, failed);
+}
+EXPORT_SYMBOL(do_trace_write_msr);
+EXPORT_TRACEPOINT_SYMBOL(write_msr);
+
+void do_trace_read_msr(unsigned msr, u64 val, int failed)
+{
+	trace_read_msr(msr, val, failed);
+}
+EXPORT_SYMBOL(do_trace_read_msr);
+EXPORT_TRACEPOINT_SYMBOL(read_msr);
+
+void do_trace_rdpmc(unsigned counter, u64 val, int failed)
+{
+	trace_rdpmc(counter, val, failed);
+}
+EXPORT_SYMBOL(do_trace_rdpmc);
+EXPORT_TRACEPOINT_SYMBOL(rdpmc);
+
+#endif
-- 
cgit