vduse: Support querying information of IOVA regions

This introduces a new ioctl: VDUSE_IOTLB_GET_INFO to
support querying some information of IOVA regions.

Now it can be used to query whether the IOVA region
supports userspace memory registration.
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Message-Id: <20220803045523.23851-6-xieyongji@bytedance.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vdpa/vdpa_user/vduse_dev.c

@@ -1228,6 +1228,45 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
 					   umem.size);
 		break;
 	}
+	case VDUSE_IOTLB_GET_INFO: {
+		struct vduse_iova_info info;
+		struct vhost_iotlb_map *map;
+		struct vduse_iova_domain *domain = dev->domain;
+
+		ret = -EFAULT;
+		if (copy_from_user(&info, argp, sizeof(info)))
+			break;
+
+		ret = -EINVAL;
+		if (info.start > info.last)
+			break;
+
+		if (!is_mem_zero((const char *)info.reserved,
+				 sizeof(info.reserved)))
+			break;
+
+		spin_lock(&domain->iotlb_lock);
+		map = vhost_iotlb_itree_first(domain->iotlb,
+					      info.start, info.last);
+		if (map) {
+			info.start = map->start;
+			info.last = map->last;
+			info.capability = 0;
+			if (domain->bounce_map && map->start == 0 &&
+			    map->last == domain->bounce_size - 1)
+				info.capability |= VDUSE_IOVA_CAP_UMEM;
+		}
+		spin_unlock(&domain->iotlb_lock);
+		if (!map)
+			break;
+
+		ret = -EFAULT;
+		if (copy_to_user(argp, &info, sizeof(info)))
+			break;
+
+		ret = 0;
+		break;
+	}
 	default:
 		ret = -ENOIOCTLCMD;
 		break;

include/uapi/linux/vduse.h

@@ -233,6 +233,30 @@ struct vduse_iova_umem {
 /* De-register the userspace memory. Caller should set iova and size field. */
 #define VDUSE_IOTLB_DEREG_UMEM	_IOW(VDUSE_BASE, 0x19, struct vduse_iova_umem)
 
+/**
+ * struct vduse_iova_info - information of one IOVA region
+ * @start: start of the IOVA region
+ * @last: last of the IOVA region
+ * @capability: capability of the IOVA regsion
+ * @reserved: for future use, needs to be initialized to zero
+ *
+ * Structure used by VDUSE_IOTLB_GET_INFO ioctl to get information of
+ * one IOVA region.
+ */
+struct vduse_iova_info {
+	__u64 start;
+	__u64 last;
+#define VDUSE_IOVA_CAP_UMEM (1 << 0)
+	__u64 capability;
+	__u64 reserved[3];
+};
+
+/*
+ * Find the first IOVA region that overlaps with the range [start, last]
+ * and return some information on it. Caller should set start and last fields.
+ */
+#define VDUSE_IOTLB_GET_INFO	_IOWR(VDUSE_BASE, 0x1a, struct vduse_iova_info)
+
 /* The control messages definition for read(2)/write(2) on /dev/vduse/$NAME */
 
 /**