Protected Execution Context Switching with Selective Save and Lazy Restore
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Solution Overview
Problem
Saving and restoring the context of processors in protected execution environments is inefficient due to the high power consumption and latency associated with saving and restoring a substantial amount of context, especially when frequent asynchronous exits occur, which limits performance.
Innovation Solution
Implementing a context save and restore unit with selective save, sanitize, and lazy restore mechanisms that utilize context metadata to determine which context elements have been modified or accessed, allowing only modified elements to be saved or sanitized, and restoring them on demand, thereby reducing unnecessary operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all context elements are saved and restored during thread switching, then context integrity is maintained, but power consumption and latency increase
Solution Approach 1:
The context is segmented into individual context elements, each tracked with metadata indicating whether it has been modified. Only modified context elements are saved and restored, rather than saving the entire context. This segmentation allows selective processing of only the necessary portions of the context, reducing power consumption while maintaining integrity of the modified elements.
Solution Approach 2:
Instead of performing the complete action of saving and restoring all context elements, the system performs partial action by saving and restoring only the modified context elements. The metadata tracking mechanism identifies which elements require saving, enabling the system to do just enough work to maintain context integrity without the excessive overhead of processing unchanged elements.
2Reliability
If all context elements are saved and restored during thread switching, then context integrity is maintained, but switching latency increases
Solution Approach 1:
The context switching operation is segmented into individual element operations based on modification status. The system identifies and processes only modified context elements, breaking down the monolithic save/restore operation into smaller, selective operations. This reduces the total time required for context switching while ensuring that all modified elements are properly preserved.
Solution Approach 2:
The system performs partial context saving by identifying modified context elements through metadata and saving only those elements. This partial action approach eliminates the time overhead of saving and restoring unchanged context elements, significantly reducing switching latency while maintaining the necessary context integrity for thread resumption.
3Reliability
If frequent asynchronous exits are handled with full context saves, then context reliability is maintained, but performance deteriorates
Solution Approach 1:
The system performs preliminary action by maintaining metadata that tracks modifications to context elements before actual context saving is needed. This preliminary tracking allows the system to quickly identify which context elements require saving during asynchronous exits, eliminating the need for full context saves and thereby maintaining performance during frequent exit operations while preserving context reliability.
Solution Approach 2:
During frequent asynchronous exits, the system performs partial context saving by processing only the modified context elements identified through metadata tracking. This approach avoids the excessive overhead of saving unchanged elements during each exit, maintaining high performance even under frequent exit conditions while ensuring that all modified context is reliably preserved for correct thread resumption.
Data Source
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AI summary
An apparatus of an aspect includes a context storage to store context of a logical processor, and an execution unit coupled with the context storage. The execution unit to perform operations corresponding to a control primitive or an exceptional condition. The operations including to selectively save a first subset of the context, from a first subset of the context storage written to after entrance into a protected execution environment, to system memory, and cause the logical processor to exit the protected execution environment. Other apparatus, methods, systems, and instructions are disclosed.