[PATCH v6 02/11] KVM: arm64: PMU: Set the default PMU for the guest on vCPU reset

[Raghavendra Rao Ananta <rananta@google.com>]

From: Reiji Watanabe <reijiw@google.com>

The following patches will use the number of counters information
from the arm_pmu and use this to set the PMCR.N for the guest
during vCPU reset. However, since the guest is not associated
with any arm_pmu until userspace configures the vPMU device
attributes, and a reset can happen before this event, call
kvm_arm_support_pmu_v3() just before doing the reset.

No functional change intended.

Signed-off-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
---
 arch/arm64/kvm/pmu-emul.c | 12 ++----------
 arch/arm64/kvm/reset.c    | 18 +++++++++++++-----
 include/kvm/arm_pmu.h     |  6 ++++++
 3 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index fb9817bdfeb57..998e1bbd5310d 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -717,8 +717,7 @@ static struct arm_pmu *kvm_pmu_probe_armpmu(void)
 	 * It is still necessary to get a valid cpu, though, to probe for the
 	 * default PMU instance as userspace is not required to specify a PMU
 	 * type. In order to uphold the preexisting behavior KVM selects the
-	 * PMU instance for the core where the first call to the
-	 * KVM_ARM_VCPU_PMU_V3_CTRL attribute group occurs. A dependent use case
+	 * PMU instance for the core during the vcpu reset. A dependent use case
 	 * would be a user with disdain of all things big.LITTLE that affines
 	 * the VMM to a particular cluster of cores.
 	 *
@@ -893,7 +892,7 @@ static void kvm_arm_set_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu)
  * where vCPUs can be scheduled on any core but the guest
  * counters could stop working.
  */
-static int kvm_arm_set_default_pmu(struct kvm *kvm)
+int kvm_arm_set_default_pmu(struct kvm *kvm)
 {
 	struct arm_pmu *arm_pmu = kvm_pmu_probe_armpmu();
 
@@ -946,13 +945,6 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	if (vcpu->arch.pmu.created)
 		return -EBUSY;
 
-	if (!kvm->arch.arm_pmu) {
-		int ret = kvm_arm_set_default_pmu(kvm);
-
-		if (ret)
-			return ret;
-	}
-
 	switch (attr->attr) {
 	case KVM_ARM_VCPU_PMU_V3_IRQ: {
 		int __user *uaddr = (int __user *)(long)attr->addr;
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 7a65a35ee4ac4..6912832b44b6d 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -206,6 +206,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)
  */
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 {
+	struct kvm *kvm = vcpu->kvm;
 	struct vcpu_reset_state reset_state;
 	int ret;
 	bool loaded;
@@ -216,6 +217,18 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 	vcpu->arch.reset_state.reset = false;
 	spin_unlock(&vcpu->arch.mp_state_lock);
 
+	if (kvm_vcpu_has_pmu(vcpu)) {
+		if (!kvm_arm_support_pmu_v3())
+			return -EINVAL;
+
+		/*
+		 * When the vCPU has a PMU, but no PMU is set for the guest
+		 * yet, set the default one.
+		 */
+		if (unlikely(!kvm->arch.arm_pmu) && kvm_arm_set_default_pmu(kvm))
+			return -EINVAL;
+	}
+
 	/* Reset PMU outside of the non-preemptible section */
 	kvm_pmu_vcpu_reset(vcpu);
 
@@ -255,11 +268,6 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 	else
 		pstate = VCPU_RESET_PSTATE_EL1;
 
-	if (kvm_vcpu_has_pmu(vcpu) && !kvm_arm_support_pmu_v3()) {
-		ret = -EINVAL;
-		goto out;
-	}
-
 	/* Reset core registers */
 	memset(vcpu_gp_regs(vcpu), 0, sizeof(*vcpu_gp_regs(vcpu)));
 	memset(&vcpu->arch.ctxt.fp_regs, 0, sizeof(vcpu->arch.ctxt.fp_regs));
diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index 31029f4f7be85..b80c75d80886b 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -101,6 +101,7 @@ void kvm_vcpu_pmu_resync_el0(void);
 })
 
 u8 kvm_arm_pmu_get_pmuver_limit(void);
+int kvm_arm_set_default_pmu(struct kvm *kvm);
 
 #else
 struct kvm_pmu {
@@ -174,6 +175,11 @@ static inline u8 kvm_arm_pmu_get_pmuver_limit(void)
 }
 static inline void kvm_vcpu_pmu_resync_el0(void) {}
 
+static inline int kvm_arm_set_default_pmu(struct kvm *kvm)
+{
+	return -ENODEV;
+}
+
 #endif
 
 #endif
-- 
2.42.0.582.g8ccd20d70d-goog