[PATCH v4 29/66] KVM: arm64: nv: Configure HCR_EL2 for nested virtualization

[Marc Zyngier]

From: Jintack Lim <jintack.lim at linaro.org>

We enable nested virtualization by setting the HCR NV and NV1 bit.

When the virtual E2H bit is set, we can support EL2 register accesses
via EL1 registers from the virtual EL2 by doing trap-and-emulate. A
better alternative, however, is to allow the virtual EL2 to access EL2
register states without trap. This can be easily achieved by not traping
EL1 registers since those registers already have EL2 register states.

Signed-off-by: Jintack Lim <jintack.lim at linaro.org>
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/hyp/vhe/switch.c | 36 ++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index a238f52955c5..79789850639b 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -37,9 +37,39 @@ static void __activate_traps(struct kvm_vcpu *vcpu)
 	u64 hcr = vcpu->arch.hcr_el2;
 	u64 val;
 
-	/* Trap VM sysreg accesses if an EL2 guest is not using VHE. */
-	if (vcpu_mode_el2(vcpu) && !vcpu_el2_e2h_is_set(vcpu))
-		hcr |= HCR_TVM | HCR_TRVM;
+	if (is_hyp_ctxt(vcpu)) {
+		hcr |= HCR_NV;
+
+		if (!vcpu_el2_e2h_is_set(vcpu)) {
+			/*
+			 * For a guest hypervisor on v8.0, trap and emulate
+			 * the EL1 virtual memory control register accesses.
+			 */
+			hcr |= HCR_TVM | HCR_TRVM | HCR_NV1;
+		} else {
+			/*
+			 * For a guest hypervisor on v8.1 (VHE), allow to
+			 * access the EL1 virtual memory control registers
+			 * natively. These accesses are to access EL2 register
+			 * states.
+			 * Note that we still need to respect the virtual
+			 * HCR_EL2 state.
+			 */
+			u64 vhcr_el2 = __vcpu_sys_reg(vcpu, HCR_EL2);
+
+			/*
+			 * We already set TVM to handle set/way cache maint
+			 * ops traps, this somewhat collides with the nested
+			 * virt trapping for nVHE. So turn this off for now
+			 * here, in the hope that VHE guests won't ever do this.
+			 * TODO: find out whether it's worth to support both
+			 * cases at the same time.
+			 */
+			hcr &= ~HCR_TVM;
+
+			hcr |= vhcr_el2 & (HCR_TVM | HCR_TRVM);
+		}
+	}
 
 	___activate_traps(vcpu, hcr);
 
-- 
2.29.2