linux-kernel - [PATCH] perf/x86/amd: Don't touch the Host-Only/Guest-Only bit inside the guest

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Date:   Fri,  1 Apr 2022 16:36:59 +0800
From:   Dongli Si <kvmx86@...il.com>
To:     peterz@...radead.org, joro@...tes.org
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,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] perf/x86/amd: Don't touch the Host-Only/Guest-Only bit inside the guest

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

With nested virtualization on AMD Milan:

If "perf record" is run in an L1 hypervisor with an L2 guest,
the following warning is emitted in the L1 guest.

[] unchecked MSR access error: WRMSR to 0xc0010200 (tried to write 0x0000020000510076)
at rIP: 0xffffffff81003a50 (x86_pmu_enable_all+0x60/0x100)
[] Call Trace:
[]  <IRQ>
[]  ? x86_pmu_enable+0x146/0x300
[]  __perf_install_in_context+0x150/0x170

and

If "perf record" is run in an L2 guest,
the following warning is emitted in the L1 guest.

[] unchecked MSR access error: WRMSR to 0xc0010200 (tried to write 0x0000010000510076)
at rIP: 0xffffffff81003a50 (x86_pmu_enable_all+0x60/0x100)
[] Call Trace:
[]  <TASK>
[]  ? x86_pmu_enable+0x146/0x300
[]  __perf_install_in_context+0x150/0x170

The AMD64_EVENTSEL_HOSTONLY/AMD64_EVENTSEL_GUESTONLY bit is defined and
used on the host (L0), while the L1 hypervisor Performance Monitor Unit
should avoid such use.

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 | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index 9687a8aef01c..79bd60d6b0fd 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -8,6 +8,7 @@
 #include <linux/jiffies.h>
 #include <asm/apicdef.h>
 #include <asm/nmi.h>
+#include <asm/hypervisor.h>
 
 #include "../perf_event.h"
 
@@ -533,7 +534,15 @@ static void amd_pmu_cpu_starting(int cpu)
 	struct amd_nb *nb;
 	int i, nb_id;
 
-	cpuc->perf_ctr_virt_mask = AMD64_EVENTSEL_HOSTONLY;
+	/*
+	 * The Host-Only/Guest-Only bit can only be set on the host.
+	 * When SVM is disabled, set the Host-Only bit will cause the
+	 * performance counter to not work.
+	 */
+	if (hypervisor_is_type(X86_HYPER_NATIVE))
+		cpuc->perf_ctr_virt_mask = AMD64_EVENTSEL_HOSTONLY;
+	else
+		cpuc->perf_ctr_virt_mask = AMD64_EVENTSEL_GUESTONLY | AMD64_EVENTSEL_HOSTONLY;
 
 	if (!x86_pmu.amd_nb_constraints)
 		return;
@@ -1023,10 +1032,16 @@ __init int amd_pmu_init(void)
 	return 0;
 }
 
+/*
+ * Unmask the Host-only bit when virtualization is enabled on the Host Hypervisor
+ */
 void amd_pmu_enable_virt(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
+	if (!hypervisor_is_type(X86_HYPER_NATIVE))
+		return;
+
 	cpuc->perf_ctr_virt_mask = 0;
 
 	/* Reload all events */
@@ -1035,10 +1050,16 @@ void amd_pmu_enable_virt(void)
 }
 EXPORT_SYMBOL_GPL(amd_pmu_enable_virt);
 
+/*
+ * Mask the Host-only bit when virtualization is disabled on the Host Hypervisor
+ */
 void amd_pmu_disable_virt(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
+	if (!hypervisor_is_type(X86_HYPER_NATIVE))
+		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
-- 
2.32.0