KVM: s390: add functions to (un)register GISC with GISA

Add the Interruption Alert Mask (IAM) to the architecture specific
kvm struct. This mask in the GISA is used to define for which ISC
a GIB alert will be issued.

The functions kvm_s390_gisc_register() and kvm_s390_gisc_unregister()
are used to (un)register a GISC (guest ISC) with a virtual machine and
its GISA.

Upon successful completion, kvm_s390_gisc_register() returns the
ISC to be used for GIB alert interruptions. A negative return code
indicates an error during registration.

Theses functions will be used by other adapter types like AP and PCI to
request pass-through interruption support.
Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
Acked-by: Pierre Morel <pmorel@linux.ibm.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20190131085247.13826-12-mimu@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/include/asm/kvm_host.h

@@ -781,6 +781,9 @@ struct kvm_s390_gisa {
 			u8  reserved03[11];
 			u32 airq_count;
 		} g1;
+		struct {
+			u64 word[4];
+		} u64;
 	};
 };
 
@@ -813,8 +816,15 @@ struct kvm_s390_vsie {
 	struct page *pages[KVM_MAX_VCPUS];
 };
 
+struct kvm_s390_gisa_iam {
+	u8 mask;
+	spinlock_t ref_lock;
+	u32 ref_count[MAX_ISC + 1];
+};
+
 struct kvm_s390_gisa_interrupt {
 	struct kvm_s390_gisa *origin;
+	struct kvm_s390_gisa_iam alert;
 };
 
 struct kvm_arch{
@@ -885,6 +895,9 @@ void kvm_arch_crypto_set_masks(struct kvm *kvm, unsigned long *apm,
 extern int sie64a(struct kvm_s390_sie_block *, u64 *);
 extern char sie_exit;
 
+extern int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc);
+extern int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc);
+
 static inline void kvm_arch_hardware_disable(void) {}
 static inline void kvm_arch_check_processor_compat(void *rtn) {}
 static inline void kvm_arch_sync_events(struct kvm *kvm) {}

arch/s390/kvm/interrupt.c

@@ -222,6 +222,33 @@ static inline u8 int_word_to_isc(u32 int_word)
  */
 #define IPM_BIT_OFFSET (offsetof(struct kvm_s390_gisa, ipm) * BITS_PER_BYTE)
 
+/**
+ * gisa_set_iam - change the GISA interruption alert mask
+ *
+ * @gisa: gisa to operate on
+ * @iam: new IAM value to use
+ *
+ * Change the IAM atomically with the next alert address and the IPM
+ * of the GISA if the GISA is not part of the GIB alert list. All three
+ * fields are located in the first long word of the GISA.
+ *
+ * Returns: 0 on success
+ *          -EBUSY in case the gisa is part of the alert list
+ */
+static inline int gisa_set_iam(struct kvm_s390_gisa *gisa, u8 iam)
+{
+	u64 word, _word;
+
+	do {
+		word = READ_ONCE(gisa->u64.word[0]);
+		if ((u64)gisa != word >> 32)
+			return -EBUSY;
+		_word = (word & ~0xffUL) | iam;
+	} while (cmpxchg(&gisa->u64.word[0], word, _word) != word);
+
+	return 0;
+}
+
 static inline void gisa_set_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
 {
 	set_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
@@ -2911,6 +2938,8 @@ void kvm_s390_gisa_init(struct kvm *kvm)
 	if (!css_general_characteristics.aiv)
 		return;
 	gi->origin = &kvm->arch.sie_page2->gisa;
+	gi->alert.mask = 0;
+	spin_lock_init(&gi->alert.ref_lock);
 	kvm_s390_gisa_clear(kvm);
 	VM_EVENT(kvm, 3, "gisa 0x%pK initialized", gi->origin);
 }
@@ -2920,6 +2949,89 @@ void kvm_s390_gisa_destroy(struct kvm *kvm)
 	kvm->arch.gisa_int.origin = NULL;
 }
 
+/**
+ * kvm_s390_gisc_register - register a guest ISC
+ *
+ * @kvm:  the kernel vm to work with
+ * @gisc: the guest interruption sub class to register
+ *
+ * The function extends the vm specific alert mask to use.
+ * The effective IAM mask in the GISA is updated as well
+ * in case the GISA is not part of the GIB alert list.
+ * It will be updated latest when the IAM gets restored
+ * by gisa_get_ipm_or_restore_iam().
+ *
+ * Returns: the nonspecific ISC (NISC) the gib alert mechanism
+ *          has registered with the channel subsystem.
+ *          -ENODEV in case the vm uses no GISA
+ *          -ERANGE in case the guest ISC is invalid
+ */
+int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc)
+{
+	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
+
+	if (!gi->origin)
+		return -ENODEV;
+	if (gisc > MAX_ISC)
+		return -ERANGE;
+
+	spin_lock(&gi->alert.ref_lock);
+	gi->alert.ref_count[gisc]++;
+	if (gi->alert.ref_count[gisc] == 1) {
+		gi->alert.mask |= 0x80 >> gisc;
+		gisa_set_iam(gi->origin, gi->alert.mask);
+	}
+	spin_unlock(&gi->alert.ref_lock);
+
+	return gib->nisc;
+}
+EXPORT_SYMBOL_GPL(kvm_s390_gisc_register);
+
+/**
+ * kvm_s390_gisc_unregister - unregister a guest ISC
+ *
+ * @kvm:  the kernel vm to work with
+ * @gisc: the guest interruption sub class to register
+ *
+ * The function reduces the vm specific alert mask to use.
+ * The effective IAM mask in the GISA is updated as well
+ * in case the GISA is not part of the GIB alert list.
+ * It will be updated latest when the IAM gets restored
+ * by gisa_get_ipm_or_restore_iam().
+ *
+ * Returns: the nonspecific ISC (NISC) the gib alert mechanism
+ *          has registered with the channel subsystem.
+ *          -ENODEV in case the vm uses no GISA
+ *          -ERANGE in case the guest ISC is invalid
+ *          -EINVAL in case the guest ISC is not registered
+ */
+int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc)
+{
+	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
+	int rc = 0;
+
+	if (!gi->origin)
+		return -ENODEV;
+	if (gisc > MAX_ISC)
+		return -ERANGE;
+
+	spin_lock(&gi->alert.ref_lock);
+	if (gi->alert.ref_count[gisc] == 0) {
+		rc = -EINVAL;
+		goto out;
+	}
+	gi->alert.ref_count[gisc]--;
+	if (gi->alert.ref_count[gisc] == 0) {
+		gi->alert.mask &= ~(0x80 >> gisc);
+		gisa_set_iam(gi->origin, gi->alert.mask);
+	}
+out:
+	spin_unlock(&gi->alert.ref_lock);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(kvm_s390_gisc_unregister);
+
 void kvm_s390_gib_destroy(void)
 {
 	if (!gib)