KVM: arm64: Move HCRX_EL2 switch to load/put on VHE systems

Although the nVHE behaviour requires HCRX_EL2 to be switched
on each switch between host and guest, there is nothing in
this register that would affect a VHE host.

It is thus possible to save/restore this register on load/put
on VHE systems, avoiding unnecessary sysreg access on the hot
path. Additionally, it avoids unnecessary traps when running
with NV.

To achieve this, simply move the read/writes to the *_common()
helpers, which are called on load/put on VHE, and more eagerly
on nVHE.
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Jing Zhang <jingzhangos@google.com>
Link: https://lore.kernel.org/r/20230815183903.2735724-28-maz@kernel.org

arch/arm64/kvm/hyp/include/hyp/switch.h

@@ -197,6 +197,9 @@ static inline void __activate_traps_common(struct kvm_vcpu *vcpu)
 	vcpu->arch.mdcr_el2_host = read_sysreg(mdcr_el2);
 	write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
 
+	if (cpus_have_final_cap(ARM64_HAS_HCX))
+		write_sysreg_s(HCRX_GUEST_FLAGS, SYS_HCRX_EL2);
+
 	__activate_traps_hfgxtr(vcpu);
 }
 
@@ -213,6 +216,9 @@ static inline void __deactivate_traps_common(struct kvm_vcpu *vcpu)
 		vcpu_clear_flag(vcpu, PMUSERENR_ON_CPU);
 	}
 
+	if (cpus_have_final_cap(ARM64_HAS_HCX))
+		write_sysreg_s(HCRX_HOST_FLAGS, SYS_HCRX_EL2);
+
 	__deactivate_traps_hfgxtr(vcpu);
 }
 
@@ -227,9 +233,6 @@ static inline void ___activate_traps(struct kvm_vcpu *vcpu)
 
 	if (cpus_have_final_cap(ARM64_HAS_RAS_EXTN) && (hcr & HCR_VSE))
 		write_sysreg_s(vcpu->arch.vsesr_el2, SYS_VSESR_EL2);
-
-	if (cpus_have_final_cap(ARM64_HAS_HCX))
-		write_sysreg_s(HCRX_GUEST_FLAGS, SYS_HCRX_EL2);
 }
 
 static inline void ___deactivate_traps(struct kvm_vcpu *vcpu)
@@ -244,9 +247,6 @@ static inline void ___deactivate_traps(struct kvm_vcpu *vcpu)
 		vcpu->arch.hcr_el2 &= ~HCR_VSE;
 		vcpu->arch.hcr_el2 |= read_sysreg(hcr_el2) & HCR_VSE;
 	}
-
-	if (cpus_have_final_cap(ARM64_HAS_HCX))
-		write_sysreg_s(HCRX_HOST_FLAGS, SYS_HCRX_EL2);
 }
 
 static inline bool __populate_fault_info(struct kvm_vcpu *vcpu)