Redesigning Xen's Memory Sharing Mechanism for Safe and Efficient I/O Virtualization

Xen's memory sharing mechanism, called the grant mechanism, is used to share I/O buffers in guest domains' memory with a driver domain. Previous studies have identified the grant mechanism as a significant source of network I/O overhead in Xen. This paper describes a redesigned grant mechanism to significantly reduce the associated overheads. Unlike the original grant mechanism, the new mechanism allows guest domains to unilaterally issue and revoke grants. As a result, the new mechanism makes it simple for the guest OS to reduce the number of grant issue and revoke operations that are needed for I/O by taking advantage of temporal and/or spatial locality in its use of I/O buffers.