This paper presents the architecture for a selfstabilizing hypervisor able to recover itself in the presence of Byzantine faults regardless of the state it is currently in. Our architecture is applicable to wide variety of underlying hardware and software and does not require augmenting computers with special hardware. The actions representing defense and recovery strategies can be specified by a user. We describe our architecture in OS-independent terms, thus making it applicable to various virtualization infrastructures. We also provide a prototype extending the Linux-based hypervisor KVM with the self-stabilizing functionality. These features allow augmenting KVM with robustness functionality in the coming stages and moving to cloud management system architectures such as OpenStack to support more industrial scenarios.
A card guessing game is played between two players, Guesser and Dealer. At the beginning of the game, the Dealer holds a deck of n cards (labeled 1, ..., n). For n turns, the Dealer draws a card from the deck, the Guesser guesses which card was drawn, and then the card is discarded from the deck. The Guesser receives a point for each correctly guessed card.With perfect memory, a Guesser can keep track of all cards that were played so far and pick at random a card that has not appeared so far, yielding in expectation ln n correct guesses. With no memory, the best a Guesser can do will result in a single guess in expectation.We consider the case of a memory bounded Guesser that has m < n memory bits. We show that the performance of such a memory bounded Guesser depends much on the behavior of the Dealer. In more detail, we show that there is a gap between the static case, where the Dealer draws cards from a properly shuffled deck or a prearranged one, and the adaptive case, where the Dealer draws cards thoughtfully, in an adversarial manner. Specifically:1. We show a Guesser with O(log 2 n) memory bits that scores a near optimal result against any static Dealer.2. We show that no Guesser with m bits of memory can score better than O( √ m) correct guesses, thus, no Guesser can score better than min{ √ m, ln n}, i.e., the above Guesser is optimal.3. We show an efficient adaptive Dealer against which no Guesser with m memory bits can make more than ln m + 2 ln log n + O(1) correct guesses in expectation.These results are (almost) tight, and we prove them using compression arguments that harness the guessing strategy for encoding.
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