User Space Hypervisor Privileged Instruction Handling
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Solution Overview
Problem
Modern computer systems face inefficiencies and security risks when processing privileged instructions, as they often require kernel-level intervention, which can be time-consuming and resource-intensive, and expose the kernel to malicious software.
Innovation Solution
Implementing a user space hypervisor that monitors a specific memory location to execute privileged instructions on behalf of virtual machines without triggering VM exits, using instructions like UMONITOR and UMWAIT to detect and execute these instructions efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If kernel-level intervention is used to process privileged instructions, then security and control are improved, but time consumption and resource usage increase
Solution Approach 1:
A user-space monitoring thread is introduced as an intermediary between the virtual machine and the kernel. This thread monitors a predefined memory location for changes indicating privileged instruction requests, processes these requests in user space, and only intervenes with the kernel when absolutely necessary. This intermediary approach maintains security through controlled access while minimizing time consumption by handling most privileged instruction processing without kernel context switches.
2Reliability
If kernel-level intervention is used to process privileged instructions, then control and security are improved, but device complexity and resource usage increase
Solution Approach 1:
The functionality for processing privileged instructions is extracted from the kernel and relocated to user space. A user-space monitoring thread and associated data structures (predefined memory location, state storage) are created to handle privileged instruction processing independently of the kernel. This extraction reduces kernel complexity and resource usage while maintaining security through the user-space implementation.
3Reliability
If VM exits are triggered for privileged instructions, then control is improved, but productivity and performance decrease
Solution Approach 1:
A predefined memory location is established in advance as a signaling mechanism between the virtual machine and the user-space monitoring thread. The virtual machine writes to this memory location to indicate privileged instruction requests, allowing the monitoring thread to detect and process these requests proactively before they would trigger VM exits. This preliminary setup enables efficient in-user-space handling of privileged instructions while maintaining control.
4Reliability
If kernel features are used for memory protection, then security is improved, but resource consumption and processing overhead increase
Solution Approach 1:
The system implements self-service memory protection mechanisms in user space. The user-space monitoring thread independently manages the detection and processing of privileged instructions using user-space data structures, eliminating the need for continuous kernel-level memory protection enforcement. This self-service approach maintains memory protection security while significantly reducing resource consumption by operating entirely in user space.
Data Source
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AI summary
Systems and methods for enabling a hypervisor that is implemented in the user space to execute privileged instructions on behalf of the virtual machines without triggering VM exits. An example method may comprise detecting, by an exception handler of a virtual machine running on a host computer system, a request to execute a privileged instruction by the virtual machine; storing at least a part of a state of the virtual machine in a memory associated with the virtual machine; signaling, by modifying a predefined memory location in the memory associated with the VM, a request to execute a privileged instruction by a user space processing thread running on the host computer system; and pausing execution of the virtual machine.