Prefix Page Table for Virtual Machine Memory Management
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Solution Overview
Problem
In virtualized computing environments, managing prefix pages for virtual machines, especially secure virtual machines, is cumbersome for hypervisors due to the need to pin these pages in memory and maintain their host translation, and this complicates memory management, particularly when secure virtual machines prevent non-trusted hypervisors from accessing guest data.
Innovation Solution
A trusted execution environment, such as an ultravisor, is used to manage prefix page access for virtual machines by checking accessibility during execution, handling explicit and implicit accesses, and ensuring secure communication between the virtual machine and the operating system, allowing the hypervisor to maintain memory management while preserving security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the hypervisor pins prefix pages in memory and maintains host translation for virtual machines, then the virtual machines can access prefix pages reliably, but the memory management becomes cumbersome and complex
Solution Approach 1:
The patent introduces a prefix page table as an intermediary structure between the hypervisor and the prefix pages. This table maps virtual machine prefix page addresses to physical memory locations, allowing the hypervisor to manage memory without directly pinning pages or maintaining complex translation tables for each virtual machine. The intermediary structure simplifies the hypervisor's memory management while ensuring reliable prefix page accessibility.
2Reliability
If secure virtual machines prevent non-trusted hypervisors from accessing guest data, then security is improved, but the hypervisor loses the ability to access prefix pages belonging to secure guests
Solution Approach 1:
The prefix page table serves as a mediator that enables secure access patterns. The hypervisor can read entries from the table to determine which prefix pages belong to secure virtual machines, while the table structure itself remains accessible to the hypervisor for management purposes. This allows the hypervisor to operate with secure virtual machines without violating security constraints that prevent direct access to guest data.
3Reliability
If the hypervisor maintains host translation for guest prefix pages, then the virtual machines can execute correctly, but the hypervisor cannot alter its memory management scheme to avoid paging out guest prefix pages
Solution Approach 1:
The patent segments the memory management function by separating the prefix page table from the main memory management structures. The prefix page table is a dedicated structure that handles prefix page mappings independently, allowing the hypervisor to implement flexible memory management schemes for other memory regions while maintaining stable prefix page access through this specialized table.
4Adaptability or versatility
If prefix pages are mapped from dynamic hardware translation, then virtualization is achieved, but the hypervisor cannot access prefix pages belonging to secure guests
Solution Approach 1:
The prefix page table acts as an intermediary layer that bridges dynamic hardware translation and hypervisor access needs. It stores mapping information for prefix pages translated by hardware, allowing the hypervisor to read this information and manage memory without directly accessing the translated guest data, thus maintaining both virtualization and security.
Data Source
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AI summary
A virtual machine is dispatched and based on the dispatch, a determination is made as to whether a select area of memory expected to be accessible to the virtual machine and used in communication between the virtual machine and an operating system is accessible to the virtual machine. Based on determining that the select area of memory is inaccessible to the virtual machine, virtual machine execution is exited with a select interception code.