Performance and security lessons learned from virtualizing the alpha processor

Abstract

Virtualization has become much more important throughout the computer industry both to improve security and to support multiple workloads on the same hardware with effective isolation between those workloads. The most widely used chip architecture, the Intel and AMD x86 processors, have begun to support virtualization, but the initial implementations show some limitations. This paper examines the virtualization properties of the Alpha architecture with particular emphasis on features that improve performance and security. It shows how the Alpha's features of PALcode, address space numbers, software handling of translation buffer misses, lack of used and modified bits, and secure handling of unpredictable results all contribute to making virtualization of the Alpha particularly easy. The paper then compares the virtual architecture of the Alpha with Intel's and AMD's virtualization approaches for x86. It also comments briefly on Intel's virtualization technology for Itanium, IBM's zSeries and pSeries hypervisors and Sun's UltraSPARC virtualization. It particularly identifies some differences between translation buffers on x86 and translation buffers on VAX and Alpha that can have adverse performance consequences. Copyright 2007 ACM.