Runtime-aware paging mode switching

Mechanism and policy to switch between the two existing techniques to virtualize memory (Shadow Page Tables and Two Dimensional Paging), depending on the VM's current workload.

Includes

• Patch against Linux Kernel v4.19.67, commit a5aa80588fcd5520ece36121c41b7d8e72245e33
  • Adds paging mode switching capability to KVM.
  • Userspace can choose initial paging mode (default: Shadow Page Tables)
• One-line patch against QEMU v4.2.92, commit 17e1e49814096a3daaa8e5a73acd56a0f30bdc18
  • Necessary to start a VM with Two Dimensional Paging
• Script to drive the mechanism
  • Monitors certain metrics with the perf tool
  • Dynamic thresholds-based policy
  • Config file to change various parameters