linux-kernel - [PATCH 10/21] perf/x86/intel: Check Arch LBR MSRs

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Date:   Fri, 19 Jun 2020 07:03:58 -0700
From:   kan.liang@...ux.intel.com
To:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        tglx@...utronix.de, bp@...en8.de, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, dave.hansen@...el.com,
        yu-cheng.yu@...el.com, bigeasy@...utronix.de, gorcunov@...il.com,
        hpa@...or.com, alexey.budankov@...ux.intel.com, eranian@...gle.com,
        ak@...ux.intel.com, like.xu@...ux.intel.com,
        yao.jin@...ux.intel.com, Kan Liang <kan.liang@...ux.intel.com>
Subject: [PATCH 10/21] perf/x86/intel: Check Arch LBR MSRs

From: Kan Liang <kan.liang@...ux.intel.com>

The KVM may not support the MSRs of Architecture LBR. Accessing the
MSRs may cause #GP and crash the guest.

The MSRs have to be checked at guest boot time.

Only using the max number of Architecture LBR depth to check the
MSR_ARCH_LBR_DEPTH should be good enough. The max number can be
calculated by 8 * the position of the last set bit of LBR_DEPTH value
in CPUID enumeration.

Co-developed-by: Like Xu <like.xu@...ux.intel.com>
Signed-off-by: Like Xu <like.xu@...ux.intel.com>
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
---
 arch/x86/events/intel/core.c | 24 ++++++++++++++++++++++--
 arch/x86/events/perf_event.h |  5 +++++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index b236cff..c3372bd 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -4145,6 +4145,8 @@ static bool check_msr(unsigned long msr, u64 mask)
 
 	if (is_lbr_from(msr))
 		val_tmp = lbr_from_signext_quirk_wr(val_tmp);
+	else if (msr == MSR_ARCH_LBR_DEPTH)
+		val_tmp = x86_pmu_get_max_arch_lbr_nr();
 
 	if (wrmsrl_safe(msr, val_tmp) ||
 	    rdmsrl_safe(msr, &val_new))
@@ -5188,8 +5190,23 @@ __init int intel_pmu_init(void)
 	 * Check all LBT MSR here.
 	 * Disable LBR access if any LBR MSRs can not be accessed.
 	 */
-	if (x86_pmu.lbr_nr && !check_msr(x86_pmu.lbr_tos, 0x3UL))
-		x86_pmu.lbr_nr = 0;
+	if (x86_pmu.lbr_nr) {
+		if (x86_pmu.arch_lbr) {
+			u64 mask = 1;
+
+			if (x86_pmu.arch_lbr_cpl)
+				mask |= ARCH_LBR_CTL_CPL;
+			if (x86_pmu.arch_lbr_filter)
+				mask |= ARCH_LBR_CTL_FILTER;
+			if (x86_pmu.arch_lbr_call_stack)
+				mask |= ARCH_LBR_CTL_STACK;
+			if (!check_msr(MSR_ARCH_LBR_CTL, mask))
+				x86_pmu.lbr_nr = 0;
+			if (!check_msr(MSR_ARCH_LBR_DEPTH, 0))
+				x86_pmu.lbr_nr = 0;
+		} else if (!check_msr(x86_pmu.lbr_tos, 0x3UL))
+			x86_pmu.lbr_nr = 0;
+	}
 	for (i = 0; i < x86_pmu.lbr_nr; i++) {
 		if (!(check_msr(x86_pmu.lbr_from + i, 0xffffUL) &&
 		      check_msr(x86_pmu.lbr_to + i, 0xffffUL)))
@@ -5206,6 +5223,9 @@ __init int intel_pmu_init(void)
 	 */
 	if (x86_pmu.extra_regs) {
 		for (er = x86_pmu.extra_regs; er->msr; er++) {
+			/* Skip Arch LBR which is already verified */
+			if (x86_pmu.arch_lbr && (er->idx == EXTRA_REG_LBR))
+				continue;
 			er->extra_msr_access = check_msr(er->msr, 0x11UL);
 			/* Disable LBR select mapping */
 			if ((er->idx == EXTRA_REG_LBR) && !er->extra_msr_access)
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index cbfc55b..7112c51 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -853,6 +853,11 @@ static inline bool x86_pmu_has_lbr_callstack(void)
 		x86_pmu.lbr_sel_map[PERF_SAMPLE_BRANCH_CALL_STACK_SHIFT] > 0;
 }
 
+static inline int x86_pmu_get_max_arch_lbr_nr(void)
+{
+	return fls(x86_pmu.arch_lbr_depth_mask) * 8;
+}
+
 DECLARE_PER_CPU(struct cpu_hw_events, cpu_hw_events);
 
 int x86_perf_event_set_period(struct perf_event *event);
-- 
2.7.4