linux-kernel - [PATCH] perf/x86/amd: cpu_hw_events::perf_ctr_virt

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Date:   Mon, 11 Apr 2022 21:46:51 +0800
From:   Dongli Si <kvmx86@...il.com>
To:     peterz@...radead.org, joro@...tes.org, likexu@...cent.com
Cc:     liam.merwick@...cle.com, kim.phillips@....com, mingo@...nel.org,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, tglx@...utronix.de, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        jmattson@...gle.com, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] perf/x86/amd: cpu_hw_events::perf_ctr_virt_mask should only be used on host

From: Dongli Si <sidongli1997@...il.com>

perf_ctr_virt_mask is used to mask Host-Only bit when SVM is disabled,
Using it on a guest doesn't make sense and make things obscure.

Revert commit df51fe7ea1c1c
("perf/x86/amd: Don't touch the AMD64_EVENTSEL_HOSTONLY bit inside the guest"),
Because it make things a little obscure and this #GP has been fixed in KVM.

Fixes: 1018faa6cf23 ("perf/x86/kvm: Fix Host-Only/Guest-Only counting with SVM disabled")
Signed-off-by: Dongli Si <sidongli1997@...il.com>
---
 arch/x86/events/amd/core.c   | 19 ++++++++++++++++++-
 arch/x86/events/perf_event.h |  3 +--
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index 9687a8aef01c..5ac7d9410d36 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -533,7 +533,12 @@ static void amd_pmu_cpu_starting(int cpu)
 	struct amd_nb *nb;
 	int i, nb_id;
 
-	cpuc->perf_ctr_virt_mask = AMD64_EVENTSEL_HOSTONLY;
+	/*
+	 * When SVM is disabled, set the Host-Only bit will cause the
+	 * performance counter to not work.
+	 */
+	if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
+		cpuc->perf_ctr_virt_mask = AMD64_EVENTSEL_HOSTONLY;
 
 	if (!x86_pmu.amd_nb_constraints)
 		return;
@@ -1023,10 +1028,16 @@ __init int amd_pmu_init(void)
 	return 0;
 }
 
+/*
+ * Unmask the Host-only bit when SVM is enabled on the Host Hypervisor
+ */
 void amd_pmu_enable_virt(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
+	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
+		return;
+
 	cpuc->perf_ctr_virt_mask = 0;
 
 	/* Reload all events */
@@ -1035,10 +1046,16 @@ void amd_pmu_enable_virt(void)
 }
 EXPORT_SYMBOL_GPL(amd_pmu_enable_virt);
 
+/*
+ * Mask the Host-only bit when SVM is disabled on the Host Hypervisor
+ */
 void amd_pmu_disable_virt(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
+	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
+		return;
+
 	/*
 	 * We only mask out the Host-only bit so that host-only counting works
 	 * when SVM is disabled. If someone sets up a guest-only counter when
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 150261d929b9..fa1428ca60b6 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1138,10 +1138,9 @@ void x86_pmu_stop(struct perf_event *event, int flags);
 
 static inline void x86_pmu_disable_event(struct perf_event *event)
 {
-	u64 disable_mask = __this_cpu_read(cpu_hw_events.perf_ctr_virt_mask);
 	struct hw_perf_event *hwc = &event->hw;
 
-	wrmsrl(hwc->config_base, hwc->config & ~disable_mask);
+	wrmsrl(hwc->config_base, hwc->config);
 
 	if (is_counter_pair(hwc))
 		wrmsrl(x86_pmu_config_addr(hwc->idx + 1), 0);
-- 
2.32.0