Handling critical instructions Popek and Goldberg virtualization requirements
the conditions isa virtualization expressed in theorem 1 may relaxed @ expense of efficiency property. vmms non-virtualizable isas (in popek , goldberg s sense) have routinely been built.
the virtualization of such architectures requires correct handling of critical instructions, i.e., sensitive unprivileged instructions. 1 approach, known patching, adopts techniques commonly used in dynamic recompilation: critical instructions discovered @ run-time , replaced trap vmm. various mechanisms, such caching of emulation code or hardware assists, have been proposed make patching process more efficient. different approach of paravirtualization, requires guest operating systems modified (ported) before running in virtual environment.
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