[PATCH v2 24/28] KVM: arm64: Engage NV3 ERET trap elision

[Marc Zyngier]

When running on NV3 HW, always engage ERET trap elision when running
the L1 context, as there is no benefit in not doing so.

An L1 can itself engage trap elision by setting its own view of
HCRX_EL2.NVTGE==1, which will subsequently be honored.

Reviewed-by: Joey Gouly <joey.gouly at arm.com>
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/include/asm/kvm_emulate.h | 10 ++++++++++
 arch/arm64/kvm/hyp/vhe/switch.c      |  4 ++++
 2 files changed, 14 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index c562d8171d5e1..b32870a5e1236 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -706,6 +706,16 @@ static inline void vcpu_set_hcrx(struct kvm_vcpu *vcpu)
 
 		if (kvm_has_feat(kvm, ID_AA64ISAR1_EL1, LS64, LS64_V))
 			vcpu->arch.hcrx_el2 |= HCRX_EL2_EnASR;
+
+		/*
+		 * NV3 is a host-specific extension, and we always use it
+		 * when present and that the guest uses NV. It may be be
+		 * hidden from the guest though.
+		 */
+		if (cpus_have_final_cap(ARM64_HAS_NV3) &&
+		    vcpu_has_nv(vcpu) && vcpu_el2_e2h_is_set(vcpu)) {
+			vcpu->arch.hcrx_el2 |= HCRX_EL2_NVTGE;
+		}
 	}
 }
 #endif /* __ARM64_KVM_EMULATE_H__ */
diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index e823046d28796..8a39e72d8386b 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -345,6 +345,10 @@ static bool kvm_hyp_handle_eret(struct kvm_vcpu *vcpu, u64 *exit_code)
 	u64 esr = kvm_vcpu_get_esr(vcpu);
 	u64 spsr, elr, mode;
 
+	/* With NV3, the fast path is handled in HW */
+	if (cpus_have_final_cap(ARM64_HAS_NV3) && vcpu_el2_e2h_is_set(vcpu))
+		return false;
+
 	/*
 	 * Going through the whole put/load motions is a waste of time
 	 * if this is a VHE guest hypervisor returning to its own
-- 
2.47.3