linux-kernel - [PATCH v2 8/8] perf/x86/intel/lbr: add the guest

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Date:   Thu,  6 Sep 2018 19:30:56 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        pbonzini@...hat.com, ak@...ux.intel.com
Cc:     kan.liang@...el.com, peterz@...radead.org, mingo@...hat.com,
        rkrcmar@...hat.com, like.xu@...el.com, wei.w.wang@...el.com
Subject: [PATCH v2 8/8] perf/x86/intel/lbr: add the guest_lbr boolean to cpuc

From: Like Xu <like.xu@...el.com>

The host creates an lbr perf event for the guest vCPU only for the
purpose of saving/restoring the lbr stack on the vCPU context switching.
There is no need to enable the lbr functionality for this lbr perf event,
because the feature is essentially used in the vCPU.

So, we introduce the guest_lbr boolean control to cpuc, to indicate if
the lbr perf event is created for the guest. When the perf subsystem
handles this event (e.g. enable or read lbr stack on PMI) and finds it
is for the guest, it simply returns, because all we need for the perf
event is just a context switch support for the lbr stack.

Signed-off-by: Like Xu <like.xu@...el.com>
Signed-off-by: Wei Wang <wei.w.wang@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/events/intel/lbr.c  | 10 +++++++---
 arch/x86/events/perf_event.h |  1 +
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 50921d3..74f6ad9 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -481,6 +481,9 @@ void intel_pmu_lbr_add(struct perf_event *event)
 	if (!x86_pmu.lbr_nr)
 		return;
 
+	if (event->attr.exclude_host)
+		cpuc->guest_lbr = true;
+
 	cpuc->br_sel = event->hw.branch_reg.reg;
 
 	if (branch_user_callstack(cpuc->br_sel) && event->ctx->task_ctx_data) {
@@ -528,6 +531,7 @@ void intel_pmu_lbr_del(struct perf_event *event)
 		set_pv_lbr_ctrl_active(false);
 	}
 
+	cpuc->guest_lbr = false;
 	cpuc->lbr_users--;
 	WARN_ON_ONCE(cpuc->lbr_users < 0);
 	perf_sched_cb_dec(event->ctx->pmu);
@@ -537,7 +541,7 @@ void intel_pmu_lbr_enable_all(bool pmi)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
-	if (cpuc->lbr_users)
+	if (cpuc->lbr_users && !cpuc->guest_lbr)
 		__intel_pmu_lbr_enable(pmi);
 }
 
@@ -545,7 +549,7 @@ void intel_pmu_lbr_disable_all(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
-	if (cpuc->lbr_users)
+	if (cpuc->lbr_users && !cpuc->guest_lbr)
 		__intel_pmu_lbr_disable();
 }
 
@@ -679,7 +683,7 @@ void intel_pmu_lbr_read(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
-	if (!cpuc->lbr_users)
+	if (!cpuc->lbr_users || cpuc->guest_lbr)
 		return;
 
 	if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_32)
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 1562863..a91fdef 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -223,6 +223,7 @@ struct cpu_hw_events {
 	 */
 	u64				intel_ctrl_guest_mask;
 	u64				intel_ctrl_host_mask;
+	bool				guest_lbr;
 	struct perf_guest_switch_msr	guest_switch_msrs[X86_PMC_IDX_MAX];
 
 	/*
-- 
2.7.4