Chapter 2 Virtualization Understanding AMD Virtualization Technology ( …
Chapter 2 Virtualization
Understanding AMD Virtualization Technology
Solving one problem.. Creating another
We still need to map from that Guest physical memory to the actual physical memory plugged into the system. The way we do this in many cases is with a technique called Shadow Page Tables thats are what connect VMs to the actual hardware from a memory standpoint.
Better way of allocating memory
Each VM has a unique ASID value, known only to the hypervisor and the TLB hardware. The ASID is invisible to the guest OS, thus eliminating the need to modify the guest, preserving the virtual illusion and avoiding any performance degradation.
4.Allocating memory the old way
The hypervisor merely flushes the TLB every time it switches from one VM to another. This forces the tasks executing in the next VM to reload the TLB with its own page table entries.
To translate the virtual addresses seen by each application into physical DRAM memory addresses, the system relies on a map that contains references linking chunks of virtual memory to real memory.
Virtual memory technology lets a system with a limited amount of physical memory look much larger to application software.
Managing Operating System State
State: If you are writing a document, the state reflects the sentences you’ve written, the file location on the disk where the document is stored, the individual values each system resource contains, and so on. When you make a change to an individual character in your word processing document, a tiny bit of memory is changed to reflect the new state of your document.
The ability to coordinate processor access by the separate guest systems is one of the main challenges of virtualization
Memory must be carefully managed to enable multiple guests to share a single set of physical memory without allowing separate guest systems to overwrite one another’s data
Each virtual guest system must have its own data storage and the virtualization software must keep each guest system’s storage isolated.
It’s critical to ensure that each virtual system receives the appropriate network traffic.