[PATCH v2 09/14] KVM: arm64: Hide FEAT_NMI from guests

[Mark Brown]

FEAT_NMI is not yet useful to guests pending implementation of vGIC
support. Mask out the feature from the ID register and prevent guests
creating state in ALLINT.ALLINT by activating the trap on write provided
in HCRX_EL2.TALLINT when they are running. There is no trap available
for reads from ALLINT.

We do not need to check for FEAT_HCRX since it is mandatory since v8.7
and FEAT_NMI is a v8.8 feature.

Signed-off-by: Mark Brown <broonie at kernel.org>
---
 arch/arm64/kvm/hyp/include/hyp/switch.h | 6 ++++++
 arch/arm64/kvm/sys_regs.c               | 1 +
 2 files changed, 7 insertions(+)

diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index 6cbbb6c02f66..89e78c4e5cce 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -85,6 +85,9 @@ static inline void __activate_traps_common(struct kvm_vcpu *vcpu)
 		write_sysreg(ARMV8_PMU_USERENR_MASK, pmuserenr_el0);
 	}
 
+	if (cpus_have_final_cap(ARM64_HAS_NMI))
+		sysreg_clear_set_s(SYS_HCRX_EL2, 0, HCRX_EL2_TALLINT);
+
 	vcpu->arch.mdcr_el2_host = read_sysreg(mdcr_el2);
 	write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
 }
@@ -93,6 +96,9 @@ static inline void __deactivate_traps_common(struct kvm_vcpu *vcpu)
 {
 	write_sysreg(vcpu->arch.mdcr_el2_host, mdcr_el2);
 
+	if (cpus_have_final_cap(ARM64_HAS_NMI))
+		sysreg_clear_set_s(SYS_HCRX_EL2, HCRX_EL2_TALLINT, 0);
+
 	write_sysreg(0, hstr_el2);
 	if (kvm_arm_support_pmu_v3())
 		write_sysreg(0, pmuserenr_el0);
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index f4a7c5abcbca..1bd4d4109a05 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1092,6 +1092,7 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, struct sys_reg_desc const *r
 			val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MTE);
 
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_SME);
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_NMI);
 		break;
 	case SYS_ID_AA64ISAR1_EL1:
 		if (!vcpu_has_ptrauth(vcpu))
-- 
2.30.2