[PATCH 2/2] KVM: arm64: Don't access PMSELR_EL0/PMUSERENR_EL0 when no PMU is available

[Marc Zyngier]

When running under a nesting hypervisor, it isn't guaranteed that
the virtual HW will include a PMU. In which case, let's not try
to access the PMU registers in the world switch, as that'd be
deadly.

Reported-by: Andre Przywara <andre.przywara at arm.com>
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kernel/image-vars.h          | 3 +++
 arch/arm64/kvm/hyp/include/hyp/switch.h | 9 ++++++---
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index f676243abac6..32af3c865700 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -102,6 +102,9 @@ KVM_NVHE_ALIAS(__stop___kvm_ex_table);
 /* Array containing bases of nVHE per-CPU memory regions. */
 KVM_NVHE_ALIAS(kvm_arm_hyp_percpu_base);
 
+/* PMU available static key */
+KVM_NVHE_ALIAS(kvm_arm_pmu_available);
+
 #endif /* CONFIG_KVM */
 
 #endif /* __ARM64_KERNEL_IMAGE_VARS_H */
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index 84473574c2e7..75c0faa3b791 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -90,15 +90,18 @@ static inline void __activate_traps_common(struct kvm_vcpu *vcpu)
 	 * counter, which could make a PMXEVCNTR_EL0 access UNDEF at
 	 * EL1 instead of being trapped to EL2.
 	 */
-	write_sysreg(0, pmselr_el0);
-	write_sysreg(ARMV8_PMU_USERENR_MASK, pmuserenr_el0);
+	if (kvm_arm_support_pmu_v3()) {
+		write_sysreg(0, pmselr_el0);
+		write_sysreg(ARMV8_PMU_USERENR_MASK, pmuserenr_el0);
+	}
 	write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
 }
 
 static inline void __deactivate_traps_common(void)
 {
 	write_sysreg(0, hstr_el2);
-	write_sysreg(0, pmuserenr_el0);
+	if (kvm_arm_support_pmu_v3())
+		write_sysreg(0, pmuserenr_el0);
 }
 
 static inline void ___activate_traps(struct kvm_vcpu *vcpu)
-- 
2.29.2