KVM: arm64: gic-v5: Mandate architected PPI for PMU emulation on GICv5

Make it mandatory to use the architected PPI when running a GICv5
guest. Attempts to set anything other than the architected PPI (23)
are rejected.

Additionally, KVM_ARM_VCPU_PMU_V3_INIT is relaxed to no longer require
KVM_ARM_VCPU_PMU_V3_IRQ to be called for GICv5-based guests. In this
case, the architectued PPI is automatically used.

Documentation is bumped accordingly.

Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://patch.msgid.link/20260319154937.3619520-33-sascha.bischoff@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

Documentation/virt/kvm/devices/vcpu.rst

@@ -37,7 +37,8 @@ Returns:
 A value describing the PMUv3 (Performance Monitor Unit v3) overflow interrupt
 number for this vcpu. This interrupt could be a PPI or SPI, but the interrupt
 type must be same for each vcpu. As a PPI, the interrupt number is the same for
-all vcpus, while as an SPI it must be a separate number per vcpu.
+all vcpus, while as an SPI it must be a separate number per vcpu. For
+GICv5-based guests, the architected PPI (23) must be used.
 
 1.2 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_INIT
 ---------------------------------------
@@ -50,7 +51,7 @@ Returns:
 	 -EEXIST  Interrupt number already used
 	 -ENODEV  PMUv3 not supported or GIC not initialized
 	 -ENXIO   PMUv3 not supported, missing VCPU feature or interrupt
-		  number not set
+		  number not set (non-GICv5 guests, only)
 	 -EBUSY   PMUv3 already initialized
 	 =======  ======================================================
 

arch/arm64/kvm/pmu-emul.c

@@ -962,8 +962,13 @@ static int kvm_arm_pmu_v3_init(struct kvm_vcpu *vcpu)
 		if (!vgic_initialized(vcpu->kvm))
 			return -ENODEV;
 
-		if (!kvm_arm_pmu_irq_initialized(vcpu))
+		if (!kvm_arm_pmu_irq_initialized(vcpu)) {
-			return -ENXIO;
+			if (!vgic_is_v5(vcpu->kvm))
+				return -ENXIO;
+
+			/* Use the architected irq number for GICv5. */
+			vcpu->arch.pmu.irq_num = KVM_ARMV8_PMU_GICV5_IRQ;
+		}
 
 		ret = kvm_vgic_set_owner(vcpu, vcpu->arch.pmu.irq_num,
 					 &vcpu->arch.pmu);
@@ -988,6 +993,10 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int irq)
 	unsigned long i;
 	struct kvm_vcpu *vcpu;
 
+	/* On GICv5, the PMUIRQ is architecturally mandated to be PPI 23 */
+	if (vgic_is_v5(kvm) && irq != KVM_ARMV8_PMU_GICV5_IRQ)
+		return false;
+
 	kvm_for_each_vcpu(i, vcpu, kvm) {
 		if (!kvm_arm_pmu_irq_initialized(vcpu))
 			continue;

include/kvm/arm_pmu.h

@@ -12,6 +12,9 @@
 
 #define KVM_ARMV8_PMU_MAX_COUNTERS	32
 
+/* PPI #23 - architecturally specified for GICv5 */
+#define KVM_ARMV8_PMU_GICV5_IRQ		0x20000017
+
 #if IS_ENABLED(CONFIG_HW_PERF_EVENTS) && IS_ENABLED(CONFIG_KVM)
 struct kvm_pmc {
 	u8 idx;	/* index into the pmu->pmc array */
@@ -38,7 +41,7 @@ struct arm_pmu_entry {
 };
 
 bool kvm_supports_guest_pmuv3(void);
-#define kvm_arm_pmu_irq_initialized(v)	((v)->arch.pmu.irq_num >= VGIC_NR_SGIS)
+#define kvm_arm_pmu_irq_initialized(v)	((v)->arch.pmu.irq_num != 0)
 u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx);
 void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val);
 void kvm_pmu_set_counter_value_user(struct kvm_vcpu *vcpu, u64 select_idx, u64 val);