vfio-ccw: Introduce a new CRW region

This region provides a mechanism to pass a Channel Report Word
that affect vfio-ccw devices, and needs to be passed to the guest
for its awareness and/or processing.

The base driver (see crw_collect_info()) provides space for two
CRWs, as a subchannel event may have two CRWs chained together
(one for the ssid, one for the subchannel).  As vfio-ccw will
deal with everything at the subchannel level, provide space
for a single CRW to be transferred in one shot.

Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20200505122745.53208-7-farman@linux.ibm.com>
[CH: added padding to ccw_crw_region]
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

Documentation/s390/vfio-ccw.rst

@@ -298,6 +298,26 @@ This region is exposed via region type VFIO_REGION_SUBTYPE_CCW_SCHIB.
 Reading this region triggers a STORE SUBCHANNEL to be issued to the
 associated hardware.
 
+vfio-ccw crw region
+---------------------
+
+The vfio-ccw crw region is used to return Channel Report Word (CRW)
+data to userspace::
+
+  struct ccw_crw_region {
+         __u32 crw;
+         __u32 pad;
+  } __packed;
+
+This region is exposed via region type VFIO_REGION_SUBTYPE_CCW_CRW.
+
+Reading this region returns a CRW if one that is relevant for this
+subchannel (e.g. one reporting changes in channel path state) is
+pending, or all zeroes if not. If multiple CRWs are pending (including
+possibly chained CRWs), reading this region again will return the next
+one, until no more CRWs are pending and zeroes are returned. This is
+similar to how STORE CHANNEL REPORT WORD works.
+
 vfio-ccw operation details
 --------------------------
 

drivers/s390/cio/vfio_ccw_chp.c

@@ -74,3 +74,58 @@ int vfio_ccw_register_schib_dev_regions(struct vfio_ccw_private *private)
 					    VFIO_REGION_INFO_FLAG_READ,
 					    private->schib_region);
 }
+
+static ssize_t vfio_ccw_crw_region_read(struct vfio_ccw_private *private,
+					char __user *buf, size_t count,
+					loff_t *ppos)
+{
+	unsigned int i = VFIO_CCW_OFFSET_TO_INDEX(*ppos) - VFIO_CCW_NUM_REGIONS;
+	loff_t pos = *ppos & VFIO_CCW_OFFSET_MASK;
+	struct ccw_crw_region *region;
+	int ret;
+
+	if (pos + count > sizeof(*region))
+		return -EINVAL;
+
+	mutex_lock(&private->io_mutex);
+	region = private->region[i].data;
+
+	if (copy_to_user(buf, (void *)region + pos, count))
+		ret = -EFAULT;
+	else
+		ret = count;
+
+	region->crw = 0;
+
+	mutex_unlock(&private->io_mutex);
+	return ret;
+}
+
+static ssize_t vfio_ccw_crw_region_write(struct vfio_ccw_private *private,
+					 const char __user *buf, size_t count,
+					 loff_t *ppos)
+{
+	return -EINVAL;
+}
+
+static void vfio_ccw_crw_region_release(struct vfio_ccw_private *private,
+					struct vfio_ccw_region *region)
+{
+
+}
+
+const struct vfio_ccw_regops vfio_ccw_crw_region_ops = {
+	.read = vfio_ccw_crw_region_read,
+	.write = vfio_ccw_crw_region_write,
+	.release = vfio_ccw_crw_region_release,
+};
+
+int vfio_ccw_register_crw_dev_regions(struct vfio_ccw_private *private)
+{
+	return vfio_ccw_register_dev_region(private,
+					    VFIO_REGION_SUBTYPE_CCW_CRW,
+					    &vfio_ccw_crw_region_ops,
+					    sizeof(struct ccw_crw_region),
+					    VFIO_REGION_INFO_FLAG_READ,
+					    private->crw_region);
+}

drivers/s390/cio/vfio_ccw_drv.c

@@ -28,6 +28,7 @@ struct workqueue_struct *vfio_ccw_work_q;
 static struct kmem_cache *vfio_ccw_io_region;
 static struct kmem_cache *vfio_ccw_cmd_region;
 static struct kmem_cache *vfio_ccw_schib_region;
+static struct kmem_cache *vfio_ccw_crw_region;
 
 debug_info_t *vfio_ccw_debug_msg_id;
 debug_info_t *vfio_ccw_debug_trace_id;
@@ -120,6 +121,8 @@ static void vfio_ccw_sch_irq(struct subchannel *sch)
 
 static void vfio_ccw_free_regions(struct vfio_ccw_private *private)
 {
+	if (private->crw_region)
+		kmem_cache_free(vfio_ccw_crw_region, private->crw_region);
 	if (private->schib_region)
 		kmem_cache_free(vfio_ccw_schib_region, private->schib_region);
 	if (private->cmd_region)
@@ -165,6 +168,12 @@ static int vfio_ccw_sch_probe(struct subchannel *sch)
 	if (!private->schib_region)
 		goto out_free;
 
+	private->crw_region = kmem_cache_zalloc(vfio_ccw_crw_region,
+						GFP_KERNEL | GFP_DMA);
+
+	if (!private->crw_region)
+		goto out_free;
+
 	private->sch = sch;
 	dev_set_drvdata(&sch->dev, private);
 	mutex_init(&private->io_mutex);
@@ -366,6 +375,7 @@ static void vfio_ccw_debug_exit(void)
 
 static void vfio_ccw_destroy_regions(void)
 {
+	kmem_cache_destroy(vfio_ccw_crw_region);
 	kmem_cache_destroy(vfio_ccw_schib_region);
 	kmem_cache_destroy(vfio_ccw_cmd_region);
 	kmem_cache_destroy(vfio_ccw_io_region);
@@ -413,6 +423,16 @@ static int __init vfio_ccw_sch_init(void)
 		goto out_err;
 	}
 
+	vfio_ccw_crw_region = kmem_cache_create_usercopy("vfio_ccw_crw_region",
+					sizeof(struct ccw_crw_region), 0,
+					SLAB_ACCOUNT, 0,
+					sizeof(struct ccw_crw_region), NULL);
+
+	if (!vfio_ccw_crw_region) {
+		ret = -ENOMEM;
+		goto out_err;
+	}
+
 	isc_register(VFIO_CCW_ISC);
 	ret = css_driver_register(&vfio_ccw_sch_driver);
 	if (ret) {

drivers/s390/cio/vfio_ccw_ops.c

@@ -178,6 +178,10 @@ static int vfio_ccw_mdev_open(struct mdev_device *mdev)
 	if (ret)
 		goto out_unregister;
 
+	ret = vfio_ccw_register_crw_dev_regions(private);
+	if (ret)
+		goto out_unregister;
+
 	return ret;
 
 out_unregister:
@@ -389,6 +393,7 @@ static int vfio_ccw_mdev_get_irq_info(struct vfio_irq_info *info)
 {
 	switch (info->index) {
 	case VFIO_CCW_IO_IRQ_INDEX:
+	case VFIO_CCW_CRW_IRQ_INDEX:
 		info->count = 1;
 		info->flags = VFIO_IRQ_INFO_EVENTFD;
 		break;
@@ -416,6 +421,9 @@ static int vfio_ccw_mdev_set_irqs(struct mdev_device *mdev,
 	case VFIO_CCW_IO_IRQ_INDEX:
 		ctx = &private->io_trigger;
 		break;
+	case VFIO_CCW_CRW_IRQ_INDEX:
+		ctx = &private->crw_trigger;
+		break;
 	default:
 		return -EINVAL;
 	}

drivers/s390/cio/vfio_ccw_private.h

@@ -57,6 +57,7 @@ void vfio_ccw_unregister_dev_regions(struct vfio_ccw_private *private);
 
 int vfio_ccw_register_async_dev_regions(struct vfio_ccw_private *private);
 int vfio_ccw_register_schib_dev_regions(struct vfio_ccw_private *private);
+int vfio_ccw_register_crw_dev_regions(struct vfio_ccw_private *private);
 
 /**
  * struct vfio_ccw_private
@@ -71,6 +72,7 @@ int vfio_ccw_register_schib_dev_regions(struct vfio_ccw_private *private);
  * @region: additional regions for other subchannel operations
  * @cmd_region: MMIO region for asynchronous I/O commands other than START
  * @schib_region: MMIO region for SCHIB information
+ * @crw_region: MMIO region for getting channel report words
  * @num_regions: number of additional regions
  * @cp: channel program for the current I/O operation
  * @irb: irb info received from interrupt
@@ -90,13 +92,15 @@ struct vfio_ccw_private {
 	struct vfio_ccw_region *region;
 	struct ccw_cmd_region	*cmd_region;
 	struct ccw_schib_region *schib_region;
+	struct ccw_crw_region	*crw_region;
 	int num_regions;
 
 	struct channel_program	cp;
 	struct irb		irb;
 	union scsw		scsw;
 
 	struct eventfd_ctx	*io_trigger;
+	struct eventfd_ctx	*crw_trigger;
 	struct work_struct	io_work;
 } __aligned(8);
 

include/uapi/linux/vfio.h

@@ -379,6 +379,7 @@ struct vfio_region_gfx_edid {
 /* sub-types for VFIO_REGION_TYPE_CCW */
 #define VFIO_REGION_SUBTYPE_CCW_ASYNC_CMD	(1)
 #define VFIO_REGION_SUBTYPE_CCW_SCHIB		(2)
+#define VFIO_REGION_SUBTYPE_CCW_CRW		(3)
 
 /*
  * The MSIX mappable capability informs that MSIX data of a BAR can be mmapped
@@ -578,6 +579,7 @@ enum {
 
 enum {
 	VFIO_CCW_IO_IRQ_INDEX,
+	VFIO_CCW_CRW_IRQ_INDEX,
 	VFIO_CCW_NUM_IRQS
 };
 

include/uapi/linux/vfio_ccw.h

@@ -44,4 +44,13 @@ struct ccw_schib_region {
 	__u8 schib_area[SCHIB_AREA_SIZE];
 } __packed;
 
+/*
+ * Used for returning a Channel Report Word to userspace.
+ * Note: this is controlled by a capability
+ */
+struct ccw_crw_region {
+	__u32 crw;
+	__u32 pad;
+} __packed;
+
 #endif