[PATCH v4 11/38] perf/x86: Forbid PMI handler when guest own PMU

[Mingwei Zhang]

If a guest PMI is delivered after VM-exit, the KVM maskable interrupt will
be held pending until EFLAGS.IF is set. In the meantime, if the logical
processor receives an NMI for any reason at all, perf_event_nmi_handler()
will be invoked. If there is any active perf event anywhere on the system,
x86_pmu_handle_irq() will be invoked, and it will clear
IA32_PERF_GLOBAL_STATUS. By the time KVM's PMI handler is invoked, it will
be a mystery which counter(s) overflowed.

When LVTPC is using KVM PMI vecotr, PMU is owned by guest, Host NMI let
x86_pmu_handle_irq() run, x86_pmu_handle_irq() restore PMU vector to NMI
and clear IA32_PERF_GLOBAL_STATUS, this breaks guest vPMU passthrough
environment.

So modify perf_event_nmi_handler() to check perf_in_guest per cpu variable,
and if so, to simply return without calling x86_pmu_handle_irq().

Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
---
 arch/x86/events/core.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 28161d6ff26d..96a173bbbec2 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -54,6 +54,8 @@ DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = {
 	.pmu = &pmu,
 };
 
+static DEFINE_PER_CPU(bool, pmi_vector_is_nmi) = true;
+
 DEFINE_STATIC_KEY_FALSE(rdpmc_never_available_key);
 DEFINE_STATIC_KEY_FALSE(rdpmc_always_available_key);
 DEFINE_STATIC_KEY_FALSE(perf_is_hybrid);
@@ -1737,6 +1739,24 @@ perf_event_nmi_handler(unsigned int cmd, struct pt_regs *regs)
 	u64 finish_clock;
 	int ret;
 
+	/*
+	 * When guest pmu context is loaded this handler should be forbidden from
+	 * running, the reasons are:
+	 * 1. After perf_guest_enter() is called, and before cpu enter into
+	 *    non-root mode, host non-PMI NMI could happen, but x86_pmu_handle_irq()
+	 *    restore PMU to use NMI vector, which destroy KVM PMI vector setting.
+	 * 2. When VM is running, host non-PMI NMI causes VM exit, KVM will
+	 *    call host NMI handler (vmx_vcpu_enter_exit()) first before KVM save
+	 *    guest PMU context (kvm_pmu_put_guest_context()), as x86_pmu_handle_irq()
+	 *    clear global_status MSR which has guest status now, then this destroy
+	 *    guest PMU status.
+	 * 3. After VM exit, but before KVM save guest PMU context, host non-PMI NMI
+	 *    could happen, x86_pmu_handle_irq() clear global_status MSR which has
+	 *    guest status now, then this destroy guest PMU status.
+	 */
+	if (!this_cpu_read(pmi_vector_is_nmi))
+		return NMI_DONE;
+
 	/*
 	 * All PMUs/events that share this PMI handler should make sure to
 	 * increment active_events for their events.
@@ -2681,10 +2701,13 @@ static void x86_pmu_switch_guest_ctx(bool enter, void *data)
 {
 	u32 guest_lvtpc = *(u32 *)data;
 
-	if (enter)
+	if (enter) {
 		apic_write(APIC_LVTPC, guest_lvtpc);
-	else
+		this_cpu_write(pmi_vector_is_nmi, false);
+	} else {
 		apic_write(APIC_LVTPC, APIC_DM_NMI);
+		this_cpu_write(pmi_vector_is_nmi, true);
+	}
 }
 
 static struct pmu pmu = {
-- 
2.49.0.395.g12beb8f557-goog