KVM: s390: interface for suppressible I/O adapters

In order to properly implement adapter-interruption suppression, we
need a way for userspace to specify which adapters are subject to
suppression. Let's convert the existing (and unused) 'pad' field into
a 'flags' field and define a flag value for suppressible adapters.

Besides, add documentation for the interface.
Signed-off-by: Fei Li <sherrylf@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

Documentation/virtual/kvm/devices/s390_flic.txt

@@ -64,12 +64,18 @@ struct kvm_s390_io_adapter {
 	__u8 isc;
 	__u8 maskable;
 	__u8 swap;
-	__u8 pad;
+	__u8 flags;
 };
 
    id contains the unique id for the adapter, isc the I/O interruption subclass
-   to use, maskable whether this adapter may be masked (interrupts turned off)
-   and swap whether the indicators need to be byte swapped.
+   to use, maskable whether this adapter may be masked (interrupts turned off),
+   swap whether the indicators need to be byte swapped, and flags contains
+   further characteristics of the adapter.
+   Currently defined values for 'flags' are:
+   - KVM_S390_ADAPTER_SUPPRESSIBLE: adapter is subject to AIS
+     (adapter-interrupt-suppression) facility. This flag only has an effect if
+     the AIS capability is enabled.
+   Unknown flag values are ignored.
 
 
   KVM_DEV_FLIC_ADAPTER_MODIFY

arch/s390/include/asm/kvm_host.h

@@ -621,6 +621,7 @@ struct s390_io_adapter {
 	bool maskable;
 	bool masked;
 	bool swap;
+	bool suppressible;
 	struct rw_semaphore maps_lock;
 	struct list_head maps;
 	atomic_t nr_maps;

arch/s390/include/uapi/asm/kvm.h

@@ -41,9 +41,11 @@ struct kvm_s390_io_adapter {
 	__u8 isc;
 	__u8 maskable;
 	__u8 swap;
-	__u8 pad;
+	__u8 flags;
 };
 
+#define KVM_S390_ADAPTER_SUPPRESSIBLE 0x01
+
 #define KVM_S390_IO_ADAPTER_MASK 1
 #define KVM_S390_IO_ADAPTER_MAP 2
 #define KVM_S390_IO_ADAPTER_UNMAP 3

arch/s390/kvm/interrupt.c

@@ -1997,6 +1997,8 @@ static int register_io_adapter(struct kvm_device *dev,
 	adapter->maskable = adapter_info.maskable;
 	adapter->masked = false;
 	adapter->swap = adapter_info.swap;
+	adapter->suppressible = (adapter_info.flags) &
+				KVM_S390_ADAPTER_SUPPRESSIBLE;
 	dev->kvm->arch.adapters[adapter->id] = adapter;
 
 	return 0;