KVM is the dominant VM hypervisor on Linux, and relies on QEMU to realize the backends of the virtio family of devices such as virtio-blk. However, KVM/QEMU-based paravirtualization prolongs the guest I/O path with multiple context switches. As fast NVMe storage devices have been widely used, the software overhead becomes non-negligible. To shorten the I/O path, virtio-blk’s variations, vhost-kernel-blk and vhost-user-blk, respectively perform all guest I/O processing in kernel and user spaces. Unfortunately, they essentially forsake the collaboration between KVM and QEMU, sacrifice important QEMU features including live migration, snapshots, and flexible image format support. This article presents EXO, an extension of virtio-blk for efficient KVM/QEMU-based storage paravirtualization. The insight is that no matter how complex the QEMU backend’s processing is, to handle a guest I/O request, the host storage stack only needs to know the request’s guest-to-host address mapping. Therefore, we preserve the original slow I/O path of virtio-blk as a fallback, and leverage eBPF to introduce an in-kernel fast path that directly queries the address mapping without switching to the user-space backend processing. Extensive evaluation shows that EXO achieves similar or even higher performance compared to the variations (vhost-kernel-blk/vhost-user-blk) of virtio-blk, while preserving virtio-blk’s flexibility, safety, and compatibility.

Emerging memory-semantic fabrics such as CXL and UB enable direct load/store access to remote memory at byte granularity, opening new opportunities for cluster-wide memory pooling and sharing. However, building a high-performance, fault-tolerant memory pool atop such fabrics remains challenging. Systems must coordinate application transparency with heterogeneous memory topologies, ensure safe memory reuse across machines, and handle instruction-level memory failures that manifest as hardware exceptions in user code. We present Oak, a resilient, high-performance memory pool service that enables transparent and efficient memory pooling and sharing across machines via memory-semantic interconnects. Oak decouples memory metadata from control logic via a stateless global memory manager, which is backed by a distributed KV store enabling scalable, fault-tolerant orchestration. To tolerate memory faults ranging from device loss to single-page uncorrectable errors, Oak provides a lightweight kernel-user cooperative recovery mechanism that intercepts memory failures in the kernel, performs microsecond-scale recovery, and defers metadata updates to user-space asynchronously. We demonstrate Oak's practicality by building Oak-KV, a fault-tolerant, zero-copy key-value store that runs entirely on Oak-managed shared memory. Evaluations show that Oak-KV delivers higher throughput than representative baselines under both normal and failure conditions.

GPU Direct Storage (GDS) plays a vital role in GPU-based training and inference systems, leveraging Peer-to-Peer Direct Memory Access (P2P-DMA) to establish a direct data transfer path between the GPU and the storage device. The direct I/O path reduces GPU storage access latency and CPU overhead, thus improving the efficiency of data transfer. Currently, however, GDS employs a phony buffer in the host memory to interact with the Linux kernel, which results in suboptimal I/O performance, extra resource consumption, and high deployment complexity.