Handling Critical Instructions
The conditions for ISA virtualization expressed in Theorem 1 may be relaxed at the expense of the efficiency property. VMMs for non-virtualizable ISAs (in the Popek and Goldberg's sense) have routinely been built.
The virtualization of such architectures requires correct handling of critical instructions, i.e., sensitive but unprivileged instructions. One approach, known as patching, adopts techniques commonly used in dynamic recompilation: critical instructions are discovered at run-time and replaced with a trap into the VMM. Various mechanisms, such as the caching of emulation code or hardware assists, have been proposed to make the patching process more efficient. A different approach is that of paravirtualization, which requires guest operating systems to be modified (ported) before running in the virtual environment.
Read more about this topic: Popek And Goldberg Virtualization Requirements
Famous quotes containing the words handling, critical and/or instructions:
“For a novel addressed by a man to men and women of full age; which attempts to deal unaffectedly with the fret and fever, derision and disaster, that may press in the wake of the strongest passion known to humanity; to tell, without a mincing of words, of a deadly war waged between flesh and spirit; and to point the tragedy of unfulfilled aims, I am not aware that there is anything in the handling to which exception can be taken.”
—Thomas Hardy (1840–1928)
“Productive collaborations between family and school, therefore, will demand that parents and teachers recognize the critical importance of each other’s participation in the life of the child. This mutuality of knowledge, understanding, and empathy comes not only with a recognition of the child as the central purpose for the collaboration but also with a recognition of the need to maintain roles and relationships with children that are comprehensive, dynamic, and differentiated.”
—Sara Lawrence Lightfoot (20th century)
“They had supposed their formula was fixed.
They had obeyed instructions to devise
A type of cold, a type of hooded gaze.
But when the Negroes came they were perplexed.
These Negroes looked like men....”
—Gwendolyn Brooks (b. 1917)