KVM: arm64: Add helper for writing ID regs

Replace the remaining usage of IDREG() with a new helper for setting the
value of a feature ID register, with the benefit of cramming in some
extra sanity checks.
Reviewed-by: Sebastian Ott <sebott@redhat.com>
Link: https://lore.kernel.org/r/20240619174036.483943-5-oliver.upton@linux.devSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_host.h

@@ -327,7 +327,6 @@ struct kvm_arch {
 	 */
 #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];
 
@@ -1346,6 +1345,8 @@ static inline u64 *__vm_id_reg(struct kvm_arch *ka, u32 reg)
 #define kvm_read_vm_id_reg(kvm, reg)					\
 	({ u64 __val = *__vm_id_reg(&(kvm)->arch, reg); __val; })
 
+void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
+
 #define __expand_field_sign_unsigned(id, fld, val)			\
 	((u64)SYS_FIELD_VALUE(id, fld, val))
 

arch/arm64/kvm/nested.c

@@ -203,8 +203,8 @@ int kvm_init_nv_sysregs(struct kvm *kvm)
 	}
 
 	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]);
+		kvm_set_vm_id_reg(kvm, IDX_IDREG(i), limit_nv_id_reg(IDX_IDREG(i),
+								     kvm->arch.id_regs[i]));
 
 	/* VTTBR_EL2 */
 	res0 = res1 = 0;

arch/arm64/kvm/sys_regs.c

@@ -1851,7 +1851,7 @@ static int set_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
 
 	ret = arm64_check_features(vcpu, rd, val);
 	if (!ret)
-		IDREG(vcpu->kvm, id) = val;
+		kvm_set_vm_id_reg(vcpu->kvm, id, val);
 
 	mutex_unlock(&vcpu->kvm->arch.config_lock);
 
@@ -1867,6 +1867,18 @@ static int set_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
 	return ret;
 }
 
+void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val)
+{
+	u64 *p = __vm_id_reg(&kvm->arch, reg);
+
+	lockdep_assert_held(&kvm->arch.config_lock);
+
+	if (KVM_BUG_ON(kvm_vm_has_ran_once(kvm) || !p, kvm))
+		return;
+
+	*p = val;
+}
+
 static int get_raz_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
 		       u64 *val)
 {
@@ -3549,8 +3561,7 @@ static void reset_vm_ftr_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc
 	if (test_bit(KVM_ARCH_FLAG_ID_REGS_INITIALIZED, &kvm->arch.flags))
 		return;
 
-	lockdep_assert_held(&kvm->arch.config_lock);
-	IDREG(kvm, id) = reg->reset(vcpu, reg);
+	kvm_set_vm_id_reg(kvm, id, reg->reset(vcpu, reg));
 }
 
 static void reset_vcpu_ftr_id_reg(struct kvm_vcpu *vcpu,