KVM: arm64: Fix PMU probe ordering

Russell reported that since 5.13, KVM's probing of the PMU has
started to fail on his HW. As it turns out, there is an implicit
ordering dependency between the architectural PMU probing code and
and KVM's own probing. If, due to probe ordering reasons, KVM probes
before the PMU driver, it will fail to detect the PMU and prevent it
from being advertised to guests as well as the VMM.

Obviously, this is one probing too many, and we should be able to
deal with any ordering.

Add a callback from the PMU code into KVM to advertise the registration
of a host CPU PMU, allowing for any probing order.

Fixes: 5421db1be3b1 ("KVM: arm64: Divorce the perf code from oprofile helpers")
Reported-by: "Russell King (Oracle)" <linux@armlinux.org.uk>
Tested-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/YUYRKVflRtUytzy5@shell.armlinux.org.uk
Cc: stable@vger.kernel.org
diff --git a/arch/arm64/kvm/perf.c b/arch/arm64/kvm/perf.c
index f9bb3b1..c84fe24 100644
--- a/arch/arm64/kvm/perf.c
+++ b/arch/arm64/kvm/perf.c
@@ -50,9 +50,6 @@
 
 int kvm_perf_init(void)
 {
-	if (kvm_pmu_probe_pmuver() != ID_AA64DFR0_PMUVER_IMP_DEF && !is_protected_kvm_enabled())
-		static_branch_enable(&kvm_arm_pmu_available);
-
 	return perf_register_guest_info_callbacks(&kvm_guest_cbs);
 }
 
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index f5065f2..2af3c37 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -740,7 +740,14 @@
 	kvm_pmu_create_perf_event(vcpu, select_idx);
 }
 
-int kvm_pmu_probe_pmuver(void)
+void kvm_host_pmu_init(struct arm_pmu *pmu)
+{
+	if (pmu->pmuver != 0 && pmu->pmuver != ID_AA64DFR0_PMUVER_IMP_DEF &&
+	    !kvm_arm_support_pmu_v3() && !is_protected_kvm_enabled())
+		static_branch_enable(&kvm_arm_pmu_available);
+}
+
+static int kvm_pmu_probe_pmuver(void)
 {
 	struct perf_event_attr attr = { };
 	struct perf_event *event;
diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 3cbc3ba..295cc79 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -952,6 +952,8 @@
 		pmu->name, pmu->num_events,
 		has_nmi ? ", using NMIs" : "");
 
+	kvm_host_pmu_init(pmu);
+
 	return 0;
 
 out_destroy:
diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index 864b999..90f2189 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -61,7 +61,6 @@
 int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu,
 			    struct kvm_device_attr *attr);
 int kvm_arm_pmu_v3_enable(struct kvm_vcpu *vcpu);
-int kvm_pmu_probe_pmuver(void);
 #else
 struct kvm_pmu {
 };
@@ -118,8 +117,6 @@
 	return 0;
 }
 
-static inline int kvm_pmu_probe_pmuver(void) { return 0xf; }
-
 #endif
 
 #endif
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 5054802..2512e2f 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -163,6 +163,12 @@
 static inline int arm_pmu_acpi_probe(armpmu_init_fn init_fn) { return 0; }
 #endif
 
+#ifdef CONFIG_KVM
+void kvm_host_pmu_init(struct arm_pmu *pmu);
+#else
+#define kvm_host_pmu_init(x)	do { } while(0)
+#endif
+
 /* Internal functions only for core arm_pmu code */
 struct arm_pmu *armpmu_alloc(void);
 struct arm_pmu *armpmu_alloc_atomic(void);