Merge: [s390]: RHEL9 - KVM: s390: pv: don't allow userspace to set the clock under PV

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/1800

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2154283

Tested: by IBM

Build-Info: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=49687044

Commits:
6973091 KVM: s390: pv: don't allow userspace to set the clock under PV

Signed-off-by: Tobias Huschle <thuschle@redhat.com>

Approved-by: Cornelia Huck <cohuck@redhat.com>
Approved-by: Steve Best <sbest@redhat.com>

Signed-off-by: Herton R. Krzesinski <herton@redhat.com>

Author: Herton R. Krzesinski

Documentation/virt/kvm/devices/vm.rst

@@ -215,6 +215,7 @@ KVM_S390_VM_TOD_EXT).
 :Parameters: address of a buffer in user space to store the data (u8) to
 :Returns:   -EFAULT if the given address is not accessible from kernel space;
 	    -EINVAL if setting the TOD clock extension to != 0 is not supported
+	    -EOPNOTSUPP for a PV guest (TOD managed by the ultravisor)
 
 3.2. ATTRIBUTE: KVM_S390_VM_TOD_LOW
 -----------------------------------
@@ -224,6 +225,7 @@ the POP (u64).
 
 :Parameters: address of a buffer in user space to store the data (u64) to
 :Returns:    -EFAULT if the given address is not accessible from kernel space
+	     -EOPNOTSUPP for a PV guest (TOD managed by the ultravisor)
 
 3.3. ATTRIBUTE: KVM_S390_VM_TOD_EXT
 -----------------------------------
@@ -237,6 +239,7 @@ it, it is stored as 0 and not allowed to be set to a value != 0.
 	     (kvm_s390_vm_tod_clock) to
 :Returns:   -EFAULT if the given address is not accessible from kernel space;
 	    -EINVAL if setting the TOD clock extension to != 0 is not supported
+	    -EOPNOTSUPP for a PV guest (TOD managed by the ultravisor)
 
 4. GROUP: KVM_S390_VM_CRYPTO
 ============================

arch/s390/kvm/kvm-s390.c

@@ -1205,6 +1205,8 @@ static int kvm_s390_vm_get_migration(struct kvm *kvm,
 	return 0;
 }
 
+static void __kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod);
+
 static int kvm_s390_set_tod_ext(struct kvm *kvm, struct kvm_device_attr *attr)
 {
 	struct kvm_s390_vm_tod_clock gtod;
@@ -1214,7 +1216,7 @@ static int kvm_s390_set_tod_ext(struct kvm *kvm, struct kvm_device_attr *attr)
 
 	if (!test_kvm_facility(kvm, 139) && gtod.epoch_idx)
 		return -EINVAL;
-	kvm_s390_set_tod_clock(kvm, &gtod);
+	__kvm_s390_set_tod_clock(kvm, &gtod);
 
 	VM_EVENT(kvm, 3, "SET: TOD extension: 0x%x, TOD base: 0x%llx",
 		gtod.epoch_idx, gtod.tod);
@@ -1245,7 +1247,7 @@ static int kvm_s390_set_tod_low(struct kvm *kvm, struct kvm_device_attr *attr)
 			   sizeof(gtod.tod)))
 		return -EFAULT;
 
-	kvm_s390_set_tod_clock(kvm, &gtod);
+	__kvm_s390_set_tod_clock(kvm, &gtod);
 	VM_EVENT(kvm, 3, "SET: TOD base: 0x%llx", gtod.tod);
 	return 0;
 }
@@ -1257,6 +1259,16 @@ static int kvm_s390_set_tod(struct kvm *kvm, struct kvm_device_attr *attr)
 	if (attr->flags)
 		return -EINVAL;
 
+	mutex_lock(&kvm->lock);
+	/*
+	 * For protected guests, the TOD is managed by the ultravisor, so trying
+	 * to change it will never bring the expected results.
+	 */
+	if (kvm_s390_pv_is_protected(kvm)) {
+		ret = -EOPNOTSUPP;
+		goto out_unlock;
+	}
+
 	switch (attr->attr) {
 	case KVM_S390_VM_TOD_EXT:
 		ret = kvm_s390_set_tod_ext(kvm, attr);
@@ -1271,6 +1283,9 @@ static int kvm_s390_set_tod(struct kvm *kvm, struct kvm_device_attr *attr)
 		ret = -ENXIO;
 		break;
 	}
+
+out_unlock:
+	mutex_unlock(&kvm->lock);
 	return ret;
 }
 
@@ -4381,13 +4396,6 @@ static void __kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_t
 	preempt_enable();
 }
 
-void kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod)
-{
-	mutex_lock(&kvm->lock);
-	__kvm_s390_set_tod_clock(kvm, gtod);
-	mutex_unlock(&kvm->lock);
-}
-
 int kvm_s390_try_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod)
 {
 	if (!mutex_trylock(&kvm->lock))

arch/s390/kvm/kvm-s390.h

@@ -363,7 +363,6 @@ int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu);
 int kvm_s390_handle_sigp_pei(struct kvm_vcpu *vcpu);
 
 /* implemented in kvm-s390.c */
-void kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod);
 int kvm_s390_try_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod);
 long kvm_arch_fault_in_page(struct kvm_vcpu *vcpu, gpa_t gpa, int writable);
 int kvm_s390_store_status_unloaded(struct kvm_vcpu *vcpu, unsigned long addr);