Virtualization technology takes an important place for the cloud service provider (CSP) because of the rapid development of cloud computing. In order to obtain more profits, the CSP need to maximize hardware performance as much as possible while ensuring good user experience. By leveraging information such as the priority and importance of I/O requests, researchers have proposed many methods to improve program performance in Linux kernel. However, the information in virtual machines can get lost during the transfer to the host. We therefore propose an I/O assurance framework based on servicelevel objective (SLO). We firstly explore the reasons for the loss of information such as I/O request priority, and then present the key issues to be addressed for information delivering. Our framework transmits the SLO information of the threads in the virtual machine to the host machine successfully by expanding Linux kernel, the virtio protocol and KVM I/O virtualization program QEMU. What's more, we implement a scheduler based on SLO. Experimental results verify the feasibility of the proposed framework. The thread with highest priority has a throughput up to 260 KB/s while the throughput of the thread with lowest priority is 10 KB/s. we prove that the SLO information delivered by the proposed framework plays a positive role in the scheduling of the scheduler in the host machine.