[PATCH v02 4/5] perf/x86/intel: MSR_LAST_BRANCH_FROM_x quirk for ctx switch

[David Carrillo-Cisneros]

Add quirk for context switch to save/restore the value of
MSR_LAST_BRANCH_FROM_x when LBR is enabled and there is potential for
kernel addresses to be in the lbr_from register.

To test this patch, use a perf tool and kernel with the patch
next in this series. That patch removes the work around that masked
the hw bug:

  $ ./lbr_perf record --call-graph lbr -e cycles:k sleep 1

where lbr_perf is the patched perf tool, that allows to specify :k
on lbr mode. The above command will trigger a #GPF :

[  411.191445] ------------[ cut here ]------------
[  411.196015] WARNING: CPU: 28 PID: 14096 at arch/x86/mm/extable.c:65 ex_handler_wrmsr_unsafe+0x70/0x80
[  411.205123] unchecked MSR access error: WRMSR to 0x681 (tried to write 0x1fffffff81010794)
...
[  411.265962] Call Trace:
[  411.268384]  [<ffffffff8167af49>] dump_stack+0x4d/0x63
[  411.273462]  [<ffffffff810b9b15>] __warn+0xe5/0x100
[  411.278278]  [<ffffffff810b9be9>] warn_slowpath_fmt+0x49/0x50
[  411.283955]  [<ffffffff810abb40>] ex_handler_wrmsr_unsafe+0x70/0x80
[  411.290144]  [<ffffffff810abc42>] fixup_exception+0x42/0x50
[  411.295658]  [<ffffffff81079d1a>] do_general_protection+0x8a/0x160
[  411.301764]  [<ffffffff81684ec2>] general_protection+0x22/0x30
[  411.307527]  [<ffffffff810101b9>] ? intel_pmu_lbr_sched_task+0xc9/0x380
[  411.314063]  [<ffffffff81009d7c>] intel_pmu_sched_task+0x3c/0x60
[  411.319996]  [<ffffffff81003a2b>] x86_pmu_sched_task+0x1b/0x20
[  411.325762]  [<ffffffff81192a5b>] perf_pmu_sched_task+0x6b/0xb0
[  411.331610]  [<ffffffff8119746d>] __perf_event_task_sched_in+0x7d/0x150
[  411.338145]  [<ffffffff810dd9dc>] finish_task_switch+0x15c/0x200
[  411.344078]  [<ffffffff8167f894>] __schedule+0x274/0x6cc
[  411.349325]  [<ffffffff8167fdd9>] schedule+0x39/0x90
[  411.354229]  [<ffffffff81675398>] exit_to_usermode_loop+0x39/0x89
[  411.360246]  [<ffffffff810028ce>] prepare_exit_to_usermode+0x2e/0x30
[  411.366524]  [<ffffffff81683c1b>] retint_user+0x8/0x10
[  411.371599] ---[ end trace 1ed61b8a551e95d3 ]---

Signed-off-by: David Carrillo-Cisneros <davidcc@xxxxxxxxxx>
Reviewed-by: Stephane Eranian <eranian@xxxxxxxxxx>
---
 arch/x86/events/intel/lbr.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 2ee5dde..6cd7cc0 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -281,6 +281,21 @@ inline u64 lbr_from_signext_quirk_wr(u64 val)
 	return val;
 }
 
+/*
+ * If quirk is needed, ensure sign extension is 61 bits.
+ */
+
+u64 lbr_from_signext_quirk_rd(u64 val)
+{
+	if (static_branch_unlikely(&lbr_from_quirk_key))
+		/*
+		 * Quirk is on when TSX is not enabled. Therefore TSX
+		 * flags must be read as OFF.
+		 */
+		val &= ~(LBR_FROM_FLAG_IN_TX | LBR_FROM_FLAG_ABORT);
+	return val;
+}
+
 static void __intel_pmu_lbr_restore(struct x86_perf_task_context *task_ctx)
 {
 	int i;
@@ -297,7 +312,8 @@ static void __intel_pmu_lbr_restore(struct x86_perf_task_context *task_ctx)
 	tos = task_ctx->tos;
 	for (i = 0; i < tos; i++) {
 		lbr_idx = (tos - i) & mask;
-		wrmsrl(x86_pmu.lbr_from + lbr_idx, task_ctx->lbr_from[i]);
+		wrmsrl(x86_pmu.lbr_from + lbr_idx,
+			lbr_from_signext_quirk_wr(task_ctx->lbr_from[i]));
 		wrmsrl(x86_pmu.lbr_to + lbr_idx, task_ctx->lbr_to[i]);
 		if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_INFO)
 			wrmsrl(MSR_LBR_INFO_0 + lbr_idx, task_ctx->lbr_info[i]);
@@ -310,7 +326,7 @@ static void __intel_pmu_lbr_save(struct x86_perf_task_context *task_ctx)
 {
 	int i;
 	unsigned lbr_idx, mask;
-	u64 tos;
+	u64 tos, val;
 
 	if (task_ctx->lbr_callstack_users == 0) {
 		task_ctx->lbr_stack_state = LBR_NONE;
@@ -321,7 +337,8 @@ static void __intel_pmu_lbr_save(struct x86_perf_task_context *task_ctx)
 	tos = intel_pmu_lbr_tos();
 	for (i = 0; i < tos; i++) {
 		lbr_idx = (tos - i) & mask;
-		rdmsrl(x86_pmu.lbr_from + lbr_idx, task_ctx->lbr_from[i]);
+		rdmsrl(x86_pmu.lbr_from + lbr_idx, val);
+		task_ctx->lbr_from[i] = lbr_from_signext_quirk_rd(val);
 		rdmsrl(x86_pmu.lbr_to + lbr_idx, task_ctx->lbr_to[i]);
 		if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_INFO)
 			rdmsrl(MSR_LBR_INFO_0 + lbr_idx, task_ctx->lbr_info[i]);
@@ -499,6 +516,8 @@ static void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc)
 		int lbr_flags = lbr_desc[lbr_format];
 
 		rdmsrl(x86_pmu.lbr_from + lbr_idx, from);
+		from = lbr_from_signext_quirk_rd(from);
+
 		rdmsrl(x86_pmu.lbr_to   + lbr_idx, to);
 
 		if (lbr_format == LBR_FORMAT_INFO && need_info) {
-- 
2.8.0.rc3.226.g39d4020