KVM: arm64: nv: Compute NV view of idregs as a one-off

Now that we have a full copy of the idregs for each VM, there is
no point in repainting the sysregs on each access. Instead, we
can simply perform the transmation as a one-off and be done
with it.
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_host.h

@@ -306,6 +306,7 @@ struct kvm_arch {
 	 * Atomic access to multiple idregs are guarded by kvm_arch.config_lock.
 	 */
 #define IDREG_IDX(id)		(((sys_reg_CRm(id) - 1) << 3) | sys_reg_Op2(id))
+#define IDX_IDREG(idx)		sys_reg(3, 0, 0, ((idx) >> 3) + 1, (idx) & Op2_mask)
 #define IDREG(kvm, id)		((kvm)->arch.id_regs[IDREG_IDX(id)])
 #define KVM_ARM_ID_REG_NUM	(IDREG_IDX(sys_reg(3, 0, 0, 7, 7)) + 1)
 	u64 id_regs[KVM_ARM_ID_REG_NUM];

arch/arm64/include/asm/kvm_nested.h

@@ -14,10 +14,6 @@ static inline bool vcpu_has_nv(const struct kvm_vcpu *vcpu)
 
 extern bool __check_nv_sr_forward(struct kvm_vcpu *vcpu);
 
-struct sys_reg_params;
-struct sys_reg_desc;
-
-void access_nested_id_reg(struct kvm_vcpu *v, struct sys_reg_params *p,
-			  const struct sys_reg_desc *r);
+int kvm_init_nv_sysregs(struct kvm *kvm);
 
 #endif /* __ARM64_KVM_NESTED_H */

arch/arm64/kvm/arm.c

@@ -669,6 +669,12 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
 			return ret;
 	}
 
+	if (vcpu_has_nv(vcpu)) {
+		ret = kvm_init_nv_sysregs(vcpu->kvm);
+		if (ret)
+			return ret;
+	}
+
 	ret = kvm_timer_enable(vcpu);
 	if (ret)
 		return ret;

arch/arm64/kvm/nested.c

@@ -23,13 +23,9 @@
  * This list should get updated as new features get added to the NV
  * support, and new extension to the architecture.
  */
-void access_nested_id_reg(struct kvm_vcpu *v, struct sys_reg_params *p,
-			  const struct sys_reg_desc *r)
+static u64 limit_nv_id_reg(u32 id, u64 val)
 {
-	u32 id = reg_to_encoding(r);
-	u64 val, tmp;
-
-	val = p->regval;
+	u64 tmp;
 
 	switch (id) {
 	case SYS_ID_AA64ISAR0_EL1:
@@ -158,5 +154,17 @@ void access_nested_id_reg(struct kvm_vcpu *v, struct sys_reg_params *p,
 		break;
 	}
 
-	p->regval = val;
+	return val;
+}
+int kvm_init_nv_sysregs(struct kvm *kvm)
+{
+	mutex_lock(&kvm->arch.config_lock);
+
+	for (int i = 0; i < KVM_ARM_ID_REG_NUM; i++)
+		kvm->arch.id_regs[i] = limit_nv_id_reg(IDX_IDREG(i),
+						       kvm->arch.id_regs[i]);
+
+	mutex_unlock(&kvm->arch.config_lock);
+
+	return 0;
 }

arch/arm64/kvm/sys_regs.c

@@ -1505,8 +1505,6 @@ static bool access_id_reg(struct kvm_vcpu *vcpu,
 		return write_to_read_only(vcpu, p, r);
 
 	p->regval = read_id_reg(vcpu, r);
-	if (vcpu_has_nv(vcpu))
-		access_nested_id_reg(vcpu, p, r);
 
 	return true;
 }