KVM: arm64: pmu: Set the CHAINED attribute before creating the in-kernel event

The current convention for KVM to request a chained event from the
host PMU is to set bit[0] in attr.config1 (PERF_ATTR_CFG1_KVM_PMU_CHAINED).

But as it turns out, this bit gets set *after* we create the kernel
event that backs our virtual counter, meaning that we never get
a 64bit counter.

Moving the setting to an earlier point solves the problem.

Fixes: 80f393a23be6 ("KVM: arm/arm64: Support chained PMU counters")
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index c30c3a7..f291d4a 100644 (file)
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c
@@ -569,12 +569,12 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
                 * high counter.
                 */
                attr.sample_period = (-counter) & GENMASK(63, 0);
+               if (kvm_pmu_counter_is_enabled(vcpu, pmc->idx + 1))
+                       attr.config1 |= PERF_ATTR_CFG1_KVM_PMU_CHAINED;
+
                event = perf_event_create_kernel_counter(&attr, -1, current,
                                                         kvm_pmu_perf_overflow,
                                                         pmc + 1);
-
-               if (kvm_pmu_counter_is_enabled(vcpu, pmc->idx + 1))
-                       attr.config1 |= PERF_ATTR_CFG1_KVM_PMU_CHAINED;
        } else {
                /* The initial sample period (overflow count) of an event. */
                if (kvm_pmu_idx_is_64bit(vcpu, pmc->idx))