KVM: arm64: PMU: Assume PMU presence in pmu-emul.c

Many functions in pmu-emul.c checks kvm_vcpu_has_pmu(vcpu). A favorable
interpretation is defensive programming, but it also has downsides:

- It is confusing as it implies these functions are called without PMU
  although most of them are called only when a PMU is present.

- It makes semantics of functions fuzzy. For example, calling
  kvm_pmu_disable_counter_mask() without PMU may result in no-op as
  there are no enabled counters, but it's unclear what
  kvm_pmu_get_counter_value() returns when there is no PMU.

- It allows callers without checking kvm_vcpu_has_pmu(vcpu), but it is
  often wrong to call these functions without PMU.

- It is error-prone to duplicate kvm_vcpu_has_pmu(vcpu) checks into
  multiple functions. Many functions are called for system registers,
  and the system register infrastructure already employs less
  error-prone, comprehensive checks.

Check kvm_vcpu_has_pmu(vcpu) in callers of these functions instead,
and remove the obsolete checks from pmu-emul.c. The only exceptions are
the functions that implement ioctls as they have definitive semantics
even when the PMU is not present.

Signed-off-by: Akihiko Odaki <[email protected]>
Reviewed-by: Marc Zyngier <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Oliver Upton <[email protected]>

1 files changed, 4 insertions, 2 deletions

diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
index 607d37bab70b..9293fb078fc6 100644
--- a/arch/arm64/kvm/emulate-nested.c
+++ b/arch/arm64/kvm/emulate-nested.c
@@ -2516,7 +2516,8 @@ void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu)
 	kvm_arch_vcpu_load(vcpu, smp_processor_id());
 	preempt_enable();
 
-	kvm_pmu_nested_transition(vcpu);
+	if (kvm_vcpu_has_pmu(vcpu))
+		kvm_pmu_nested_transition(vcpu);
 }
 
 static void kvm_inject_el2_exception(struct kvm_vcpu *vcpu, u64 esr_el2,
@@ -2599,7 +2600,8 @@ static int kvm_inject_nested(struct kvm_vcpu *vcpu, u64 esr_el2,
 	kvm_arch_vcpu_load(vcpu, smp_processor_id());
 	preempt_enable();
 
-	kvm_pmu_nested_transition(vcpu);
+	if (kvm_vcpu_has_pmu(vcpu))
+		kvm_pmu_nested_transition(vcpu);
 
 	return 1;
 }