[PATCH v4 2/7] KVM: arm64: PMU: Assume PMU presence in pmu-emul.c

[Akihiko Odaki <akihiko.odaki@daynix.com>]

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 <akihiko.odaki@daynix.com>
---
 arch/arm64/kvm/arm.c      |  8 +++++---
 arch/arm64/kvm/pmu-emul.c | 25 +------------------------
 arch/arm64/kvm/sys_regs.c |  6 ++++--
 3 files changed, 10 insertions(+), 29 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index f66ce098f03b..e375468a2217 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -834,9 +834,11 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
 	if (ret)
 		return ret;
 
-	ret = kvm_arm_pmu_v3_enable(vcpu);
-	if (ret)
-		return ret;
+	if (kvm_vcpu_has_pmu(vcpu)) {
+		ret = kvm_arm_pmu_v3_enable(vcpu);
+		if (ret)
+			return ret;
+	}
 
 	if (is_protected_kvm_enabled()) {
 		ret = pkvm_create_hyp_vm(kvm);
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index e3e82b66e226..3dd0b479c6fd 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -144,9 +144,6 @@ static u64 kvm_pmu_get_pmc_value(struct kvm_pmc *pmc)
  */
 u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
 {
-	if (!kvm_vcpu_has_pmu(vcpu))
-		return 0;
-
 	return kvm_pmu_get_pmc_value(kvm_vcpu_idx_to_pmc(vcpu, select_idx));
 }
 
@@ -185,9 +182,6 @@ static void kvm_pmu_set_pmc_value(struct kvm_pmc *pmc, u64 val, bool force)
  */
 void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val)
 {
-	if (!kvm_vcpu_has_pmu(vcpu))
-		return;
-
 	kvm_pmu_set_pmc_value(kvm_vcpu_idx_to_pmc(vcpu, select_idx), val, false);
 }
 
@@ -289,8 +283,6 @@ u64 kvm_pmu_valid_counter_mask(struct kvm_vcpu *vcpu)
 void kvm_pmu_enable_counter_mask(struct kvm_vcpu *vcpu, u64 val)
 {
 	int i;
-	if (!kvm_vcpu_has_pmu(vcpu))
-		return;
 
 	if (!(kvm_vcpu_read_pmcr(vcpu) & ARMV8_PMU_PMCR_E) || !val)
 		return;
@@ -324,7 +316,7 @@ void kvm_pmu_disable_counter_mask(struct kvm_vcpu *vcpu, u64 val)
 {
 	int i;
 
-	if (!kvm_vcpu_has_pmu(vcpu) || !val)
+	if (!val)
 		return;
 
 	for (i = 0; i < KVM_ARMV8_PMU_MAX_COUNTERS; i++) {
@@ -357,9 +349,6 @@ static void kvm_pmu_update_state(struct kvm_vcpu *vcpu)
 	struct kvm_pmu *pmu = &vcpu->arch.pmu;
 	bool overflow;
 
-	if (!kvm_vcpu_has_pmu(vcpu))
-		return;
-
 	overflow = !!kvm_pmu_overflow_status(vcpu);
 	if (pmu->irq_level == overflow)
 		return;
@@ -555,9 +544,6 @@ void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
 {
 	int i;
 
-	if (!kvm_vcpu_has_pmu(vcpu))
-		return;
-
 	/* Fixup PMCR_EL0 to reconcile the PMU version and the LP bit */
 	if (!kvm_has_feat(vcpu->kvm, ID_AA64DFR0_EL1, PMUVer, V3P5))
 		val &= ~ARMV8_PMU_PMCR_LP;
@@ -696,9 +682,6 @@ void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
 	struct kvm_pmc *pmc = kvm_vcpu_idx_to_pmc(vcpu, select_idx);
 	u64 reg;
 
-	if (!kvm_vcpu_has_pmu(vcpu))
-		return;
-
 	reg = counter_index_to_evtreg(pmc->idx);
 	__vcpu_sys_reg(vcpu, reg) = data & kvm_pmu_evtyper_mask(vcpu->kvm);
 
@@ -804,9 +787,6 @@ u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
 	u64 val, mask = 0;
 	int base, i, nr_events;
 
-	if (!kvm_vcpu_has_pmu(vcpu))
-		return 0;
-
 	if (!pmceid1) {
 		val = compute_pmceid0(cpu_pmu);
 		base = 0;
@@ -847,9 +827,6 @@ void kvm_vcpu_reload_pmu(struct kvm_vcpu *vcpu)
 
 int kvm_arm_pmu_v3_enable(struct kvm_vcpu *vcpu)
 {
-	if (!kvm_vcpu_has_pmu(vcpu))
-		return 0;
-
 	if (!vcpu->arch.pmu.created)
 		return -EINVAL;
 
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 0a2ce931a946..6e75557bea1d 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1784,12 +1784,14 @@ static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 static u64 read_sanitised_id_dfr0_el1(struct kvm_vcpu *vcpu,
 				      const struct sys_reg_desc *rd)
 {
-	u8 perfmon = pmuver_to_perfmon(kvm_arm_pmu_get_pmuver_limit());
+	u8 perfmon;
 	u64 val = read_sanitised_ftr_reg(SYS_ID_DFR0_EL1);
 
 	val &= ~ID_DFR0_EL1_PerfMon_MASK;
-	if (kvm_vcpu_has_pmu(vcpu))
+	if (kvm_vcpu_has_pmu(vcpu)) {
+		perfmon = pmuver_to_perfmon(kvm_arm_pmu_get_pmuver_limit());
 		val |= SYS_FIELD_PREP(ID_DFR0_EL1, PerfMon, perfmon);
+	}
 
 	val = ID_REG_LIMIT_FIELD_ENUM(val, ID_DFR0_EL1, CopDbg, Debugv8p8);
 

-- 
2.48.1