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

1 files changed, 8 insertions, 1 deletions

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index f5065f23b413..2af3c37445e0 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -740,7 +740,14 @@ void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
 	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;