Memory Hierarchy Design - Computer Architecture: A Quantitative Approach - page 126

Pitfall Not Delivering High Memory Bandwidth In A Cache-based System
Caches help with average cache memory latency but may not deliver high memory bandwidth
to an application that must go to main memory. The architect must design a high bandwidth
memory behind the cache for such applications. We will revisit this pitfall in Chapters 4 and 5 .
Pitfall Implementing A Virtual Machine Monitor On An Instruction Set Architecture
That Wasn't Designed To Be Virtualizable
Many architects in the 1970s and 1980s weren't careful to make sure that all instructions read-
ing or writing information related to hardware resource infor-mation were privileged. This
laissez faire atitude causes problems for VMMs for all of these architectures, including the
80x86, which we use here as an example.
Figure 2.28 describes the 18 instructions that cause problems for virtualization [ Robin and
Irvine 2000 ] . The two broad classes are instructions that
■ Read control registers in user mode that reveal that the guest operating system is running
in a virtual machine (such as POPF mentioned earlier)
■ Check protection as required by the segmented architecture but assume that the operating
system is running at the highest privilege level.