KVM: arm64: nv: Add additional trap setup for CPTR_EL2

We need to teach KVM a couple of new tricks. CPTR_EL2 and its
VHE accessor CPACR_EL1 need to be handled specially:

- CPACR_EL1 is trapped on VHE so that we can track the TCPAC
  and TTA bits

- CPTR_EL2.{TCPAC,E0POE} are propagated from L1 to L2

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240620164653.1130714-15-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/kvm/hyp/vhe/switch.c

@@ -87,11 +87,23 @@ static void __activate_cptr_traps(struct kvm_vcpu *vcpu)
 		__activate_traps_fpsimd32(vcpu);
 	}
 
+	if (!vcpu_has_nv(vcpu))
+		goto write;
+
+	/*
+	 * The architecture is a bit crap (what a surprise): an EL2 guest
+	 * writing to CPTR_EL2 via CPACR_EL1 can't set any of TCPAC or TTA,
+	 * as they are RES0 in the guest's view. To work around it, trap the
+	 * sucker using the very same bit it can't set...
+	 */
+	if (vcpu_el2_e2h_is_set(vcpu) && is_hyp_ctxt(vcpu))
+		val |= CPTR_EL2_TCPAC;
+
 	/*
 	 * Layer the guest hypervisor's trap configuration on top of our own if
 	 * we're in a nested context.
 	 */
-	if (!vcpu_has_nv(vcpu) || is_hyp_ctxt(vcpu))
+	if (is_hyp_ctxt(vcpu))
 		goto write;
 
 	cptr = vcpu_sanitised_cptr_el2(vcpu);
@@ -115,6 +127,11 @@ static void __activate_cptr_traps(struct kvm_vcpu *vcpu)
 	if (!(SYS_FIELD_GET(CPACR_ELx, ZEN, cptr) & BIT(0)))
 		val &= ~CPACR_ELx_ZEN;
 
+	if (kvm_has_feat(vcpu->kvm, ID_AA64MMFR3_EL1, S2POE, IMP))
+		val |= cptr & CPACR_ELx_E0POE;
+
+	val |= cptr & CPTR_EL2_TCPAC;
+
 write:
 	write_sysreg(val, cpacr_el1);
 }