KVM: arm64: Add PMU event filtering infrastructure

It can be desirable to expose a PMU to a guest, and yet not want the
guest to be able to count some of the implemented events (because this
would give information on shared resources, for example.

For this, let's extend the PMUv3 device API, and offer a way to setup a
bitmap of the allowed events (the default being no bitmap, and thus no
filtering).

Userspace can thus allow/deny ranges of event. The default policy
depends on the "polarity" of the first filter setup (default deny if the
filter allows events, and default allow if the filter denies events).
This allows to setup exactly what is allowed for a given guest.

Note that although the ioctl is per-vcpu, the map of allowed events is
global to the VM (it can be setup from any vcpu until the vcpu PMU is
initialized).

Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

2 files changed, 65 insertions, 6 deletions

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 46dc3d75cf13..427848ff6f20 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -145,6 +145,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 {
 	int i;
 
+	bitmap_free(kvm->arch.pmu_filter);
+
 	kvm_vgic_destroy(kvm);
 
 	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 10d3860a9c0a..8cd365968af1 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -593,11 +593,21 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
 	data = __vcpu_sys_reg(vcpu, reg);
 
 	kvm_pmu_stop_counter(vcpu, pmc);
-	eventsel = data & kvm_pmu_event_mask(vcpu->kvm);;
+	if (pmc->idx == ARMV8_PMU_CYCLE_IDX)
+		eventsel = ARMV8_PMUV3_PERFCTR_CPU_CYCLES;
+	else
+		eventsel = data & kvm_pmu_event_mask(vcpu->kvm);
+
+	/* Software increment event doesn't need to be backed by a perf event */
+	if (eventsel == ARMV8_PMUV3_PERFCTR_SW_INCR)
+		return;
 
-	/* Software increment event does't need to be backed by a perf event */
-	if (eventsel == ARMV8_PMUV3_PERFCTR_SW_INCR &&
-	    pmc->idx != ARMV8_PMU_CYCLE_IDX)
+	/*
+	 * If we have a filter in place and that the event isn't allowed, do
+	 * not install a perf event either.
+	 */
+	if (vcpu->kvm->arch.pmu_filter &&
+	    !test_bit(eventsel, vcpu->kvm->arch.pmu_filter))
 		return;
 
 	memset(&attr, 0, sizeof(struct perf_event_attr));
@@ -609,8 +619,7 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
 	attr.exclude_kernel = data & ARMV8_PMU_EXCLUDE_EL1 ? 1 : 0;
 	attr.exclude_hv = 1; /* Don't count EL2 events */
 	attr.exclude_host = 1; /* Don't count host events */
-	attr.config = (pmc->idx == ARMV8_PMU_CYCLE_IDX) ?
-		ARMV8_PMUV3_PERFCTR_CPU_CYCLES : eventsel;
+	attr.config = eventsel;
 
 	counter = kvm_pmu_get_pair_counter_value(vcpu, pmc);
 
@@ -889,6 +898,53 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 		vcpu->arch.pmu.irq_num = irq;
 		return 0;
 	}
+	case KVM_ARM_VCPU_PMU_V3_FILTER: {
+		struct kvm_pmu_event_filter __user *uaddr;
+		struct kvm_pmu_event_filter filter;
+		int nr_events;
+
+		nr_events = kvm_pmu_event_mask(vcpu->kvm) + 1;
+
+		uaddr = (struct kvm_pmu_event_filter __user *)(long)attr->addr;
+
+		if (copy_from_user(&filter, uaddr, sizeof(filter)))
+			return -EFAULT;
+
+		if (((u32)filter.base_event + filter.nevents) > nr_events ||
+		    (filter.action != KVM_PMU_EVENT_ALLOW &&
+		     filter.action != KVM_PMU_EVENT_DENY))
+			return -EINVAL;
+
+		mutex_lock(&vcpu->kvm->lock);
+
+		if (!vcpu->kvm->arch.pmu_filter) {
+			vcpu->kvm->arch.pmu_filter = bitmap_alloc(nr_events, GFP_KERNEL);
+			if (!vcpu->kvm->arch.pmu_filter) {
+				mutex_unlock(&vcpu->kvm->lock);
+				return -ENOMEM;
+			}
+
+			/*
+			 * The default depends on the first applied filter.
+			 * If it allows events, the default is to deny.
+			 * Conversely, if the first filter denies a set of
+			 * events, the default is to allow.
+			 */
+			if (filter.action == KVM_PMU_EVENT_ALLOW)
+				bitmap_zero(vcpu->kvm->arch.pmu_filter, nr_events);
+			else
+				bitmap_fill(vcpu->kvm->arch.pmu_filter, nr_events);
+		}
+
+		if (filter.action == KVM_PMU_EVENT_ALLOW)
+			bitmap_set(vcpu->kvm->arch.pmu_filter, filter.base_event, filter.nevents);
+		else
+			bitmap_clear(vcpu->kvm->arch.pmu_filter, filter.base_event, filter.nevents);
+
+		mutex_unlock(&vcpu->kvm->lock);
+
+		return 0;
+	}
 	case KVM_ARM_VCPU_PMU_V3_INIT:
 		return kvm_arm_pmu_v3_init(vcpu);
 	}
@@ -925,6 +981,7 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	switch (attr->attr) {
 	case KVM_ARM_VCPU_PMU_V3_IRQ:
 	case KVM_ARM_VCPU_PMU_V3_INIT:
+	case KVM_ARM_VCPU_PMU_V3_FILTER:
 		if (kvm_arm_support_pmu_v3() &&
 		    test_bit(KVM_ARM_VCPU_PMU_V3, vcpu->arch.features))
 			return 0;