KVM: arm64: Define helper for ICH_VTR_EL2

Move the computation of the ICH_VTR_EL2 value to a common location,
so that it can be reused by the save/restore code.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250714122634.3334816-5-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: Marc Zyngier

arch/arm64/kvm/sys_regs.c

@@ -2521,11 +2521,7 @@ static bool access_gic_vtr(struct kvm_vcpu *vcpu,
 	if (p->is_write)
 		return write_to_read_only(vcpu, p, r);
 
-	p->regval = kvm_vgic_global_state.ich_vtr_el2;
-	p->regval &= ~(ICH_VTR_EL2_DVIM 	|
-		       ICH_VTR_EL2_A3V		|
-		       ICH_VTR_EL2_IDbits);
-	p->regval |= ICH_VTR_EL2_nV4;
+	p->regval = kvm_get_guest_vtr_el2();
 
 	return true;
 }

arch/arm64/kvm/vgic/vgic.h

@@ -66,6 +66,21 @@
 
 #define KVM_ICC_SRE_EL2		(ICC_SRE_EL2_ENABLE | ICC_SRE_EL2_SRE |	\
 				 ICC_SRE_EL1_DIB | ICC_SRE_EL1_DFB)
+#define KVM_ICH_VTR_EL2_RES0	(ICH_VTR_EL2_DVIM 	|	\
+				 ICH_VTR_EL2_A3V	|	\
+				 ICH_VTR_EL2_IDbits)
+#define KVM_ICH_VTR_EL2_RES1	ICH_VTR_EL2_nV4
+
+static inline u64 kvm_get_guest_vtr_el2(void)
+{
+	u64 vtr;
+
+	vtr  = kvm_vgic_global_state.ich_vtr_el2;
+	vtr &= ~KVM_ICH_VTR_EL2_RES0;
+	vtr |= KVM_ICH_VTR_EL2_RES1;
+
+	return vtr;
+}
 
 /*
  * As per Documentation/virt/kvm/devices/arm-vgic-its.rst,