[PATCH v8 10/11] KVM: arm64: PMU: Introduce FIXED_COUNTERS_ONLY

Introduce the KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY attribute to
create a "fixed-counters-only" PMU.

Much like KVM_ARM_VCPU_PMU_V3_IRQ and other read-write attributes, this
attribute provides a getter that facilitates kernel and userspace
debugging/testing.

Signed-off-by: Akihiko Odaki <[email protected]>
---
 Documentation/virt/kvm/devices/vcpu.rst | 30 ++++++++++++++++++++++++++----
 arch/arm64/include/uapi/asm/kvm.h       |  1 +
 arch/arm64/kvm/pmu-emul.c               | 26 +++++++++++++++++++++++++-
 3 files changed, 52 insertions(+), 5 deletions(-)

diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
index 5e3805820010..b7ac4a545ffb 100644
--- a/Documentation/virt/kvm/devices/vcpu.rst
+++ b/Documentation/virt/kvm/devices/vcpu.rst
@@ -71,7 +71,8 @@ irqchip.
 	 -ENODEV  PMUv3 not supported or GIC not initialized
 	 -ENXIO   PMUv3 not properly configured or in-kernel irqchip not
 	 	  configured as required prior to calling this attribute
-	 -EBUSY   PMUv3 already initialized or a VCPU has already run
+	 -EBUSY   PMUv3 already initialized, a VCPU has already run or
+		  FIXED_COUNTERS_ONLY has already been set
 	 -EINVAL  Invalid filter range
 	 =======  ======================================================
 
@@ -113,14 +114,14 @@ using event 0x11 (CPU_CYCLES).
 
 :Returns:
 
-	 =======  ====================================================
+	 =======  ===========================================================
 	 -EBUSY   PMUv3 already initialized, a VCPU has already run or
-                  an event filter has already been set
+                  an event filter or FIXED_COUNTERS_ONLY has already been set
 	 -EFAULT  Error accessing the PMU identifier
 	 -ENXIO   PMU not found
 	 -ENODEV  PMUv3 not supported or GIC not initialized
 	 -ENOMEM  Could not allocate memory
-	 =======  ====================================================
+	 =======  ===========================================================
 
 Request that the VCPU uses the specified hardware PMU when creating guest events
 for the purpose of PMU emulation. The PMU identifier can be read from the "type"
@@ -162,6 +163,27 @@ explicitly selected, or the number of counters is out of range for the
 selected PMU. Selecting a new PMU cancels the effect of setting this
 attribute.
 
+1.6 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY
+------------------------------------------------------
+
+:Parameters: no additional parameter in kvm_device_attr.addr
+
+:Returns:
+
+	 =======  ==================================================
+	 -EBUSY   PMUv3 already initialized, a VCPU has already run,
+		  an event filter has already been set or
+		  a hardware PMU has already been specified
+	 -ENXIO   Attempted to get before setting
+	 -ENODEV  Attempted to set while PMUv3 not supported
+	 =======  ==================================================
+
+If set, KVM emulates PMUv3 without programmable event counters.
+
+When this attribute is enabled, the vCPU can run on any physical CPU
+that has a PMU, regardless of the underlying implementation. This
+attribute is VM-scoped.
+
 2. GROUP: KVM_ARM_VCPU_TIMER_CTRL
 =================================
 
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 1c13bfa2d38a..39a1a1e412e6 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -437,6 +437,7 @@ enum {
 #define   KVM_ARM_VCPU_PMU_V3_FILTER		2
 #define   KVM_ARM_VCPU_PMU_V3_SET_PMU		3
 #define   KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS	4
+#define   KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY	5
 #define KVM_ARM_VCPU_TIMER_CTRL		1
 #define   KVM_ARM_VCPU_TIMER_IRQ_VTIMER		0
 #define   KVM_ARM_VCPU_TIMER_IRQ_PTIMER		1
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 1aa115aee781..89d63e5fffec 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -1150,11 +1150,13 @@ static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id)
 		arm_pmu = entry->arm_pmu;
 		if (arm_pmu->pmu.type == pmu_id) {
 			if (kvm_vm_has_ran_once(kvm) ||
+			    kvm_pmu_fixed_counters_only(kvm) ||
 			    (kvm->arch.pmu_filter && kvm->arch.arm_pmu != arm_pmu)) {
 				ret = -EBUSY;
 				break;
 			}
 
+			set_bit(KVM_ARCH_FLAG_PMU_V3_EXPLICIT, &kvm->arch.flags);
 			kvm_arm_set_pmu(kvm, arm_pmu);
 			cpumask_copy(kvm->arch.supported_cpus, &arm_pmu->supported_cpus);
 			ret = 0;
@@ -1165,6 +1167,22 @@ static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id)
 	return ret;
 }
 
+static int kvm_arm_pmu_v3_set_pmu_fixed_counters_only(struct kvm_vcpu *vcpu)
+{
+	struct kvm *kvm = vcpu->kvm;
+
+	lockdep_assert_held(&kvm->arch.config_lock);
+
+	if (kvm_vm_has_ran_once(kvm) || kvm->arch.pmu_filter ||
+	    test_bit(KVM_ARCH_FLAG_PMU_V3_EXPLICIT, &kvm->arch.flags))
+		return -EBUSY;
+
+	set_bit(KVM_ARCH_FLAG_PMU_V3_FIXED_COUNTERS_ONLY, &kvm->arch.flags);
+	kvm_arm_set_nr_counters(kvm, 0);
+
+	return 0;
+}
+
 static int kvm_arm_pmu_v3_set_nr_counters(struct kvm_vcpu *vcpu, unsigned int n)
 {
 	struct kvm *kvm = vcpu->kvm;
@@ -1239,7 +1257,7 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 		     filter.action != KVM_PMU_EVENT_DENY))
 			return -EINVAL;
 
-		if (kvm_vm_has_ran_once(kvm))
+		if (kvm_vm_has_ran_once(kvm) || kvm_pmu_fixed_counters_only(kvm))
 			return -EBUSY;
 
 		if (!kvm->arch.pmu_filter) {
@@ -1284,6 +1302,8 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 
 		return kvm_arm_pmu_v3_set_nr_counters(vcpu, n);
 	}
+	case KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY:
+		return kvm_arm_pmu_v3_set_pmu_fixed_counters_only(vcpu);
 	case KVM_ARM_VCPU_PMU_V3_INIT:
 		return kvm_arm_pmu_v3_init(vcpu);
 	}
@@ -1310,6 +1330,9 @@ int kvm_arm_pmu_v3_get_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 		irq = vcpu->arch.pmu.irq_num;
 		return put_user(irq, uaddr);
 	}
+	case KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY:
+		if (kvm_pmu_fixed_counters_only(vcpu->kvm))
+			return 0;
 	}
 
 	return -ENXIO;
@@ -1323,6 +1346,7 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	case KVM_ARM_VCPU_PMU_V3_FILTER:
 	case KVM_ARM_VCPU_PMU_V3_SET_PMU:
 	case KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS:
+	case KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY:
 		if (kvm_vcpu_has_pmu(vcpu))
 			return 0;
 	}

-- 
2.55.0