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Compute Virtualisation - Coggle Diagram

- - - - HostOS
      - GuestMachine
      - HostMachone
      - GuestOS
      - HyperVisor
        Virtualization software layer, or Virtual Machine Monitor (VMM)
        The core of virtualization technology between the host OS and guest OS is a hypervisor, which is sometimes called Virtual Machine Manager (VMM).
    - - Bare-Metal Virtualization
        
        This type of hypervisor has direct access to hardware resources and does not need to access the host OS. The hypervisor can be seen as a customized host OS, which merely functions as VMM and does not run other applications.The hypervisor provides the following basic functions: Identify, capture, and respond to privileged CPU instructions or protection instructions sent by VMs.
      - Physical resources are managed by the host OS (for example, Windows or Linux). VMM provides virtualization services and functions as a common application in the underlying OS (for example, Windows or Linux).
        VMs can be created using VMM to share underlying server resources. VMM obtains resources by calling the host OS services to virtualize the CPUs, memory, and I/O devices After a VM is created, VMM usually schedules the VM as a process of the host OS.
        The virtualization products that use Type 2 hypervisors include VMware Workstation and Virtual PC.
      - Containers
        Many people categorize containers as the third type of hypervisor.
      - Both Type 1 and Type 2 hypervisors possess the partitioning, isolation, encapsulation, and hardware independence features.
        
        Isolation
        
        Multiple VMs created in a partition are logically isolated from each other.
        
        Encapsulation
        
        Each VM is saved as a group of hardware-independent files, including the hardware configuration, BIOS configuration, memory status, disk status, and CPU status. encapsulating a
        VM as a set of hardware-independent files makes VM migration and hot swap possible.
        
        Partitioning
        
        Partitioning: indicates the VMM capability of allocating server resources to multiple VMs. Each VM can run an independent OS (same as or different from the OSs running on other VMs on the same server) so that multiple applications can coexist on one server.
        
        Hardware Independance
        
        After a VM is encapsulated into a group of files, the VM is
        completely independent from its underlying hardware. You can migrate the VM by copying the VM device file, configuration file, or disk file to another host. Because the underlying hardware device is shielded by VMM running on it, the migration can be successful as long as the same VMM running on the target host as that on the source host, regardless of the underlying hardware specifications and configuration.
  - - - intro
        
        Before we talk about CPU virtualization, let's have a brief look at the hierarchical protection domains of CPUs, often called protection rings. There are four rings: Ring 0, Ring 1, Ring 2, and Ring 3, which is a hierarchy of control from the most to least privilege. Ring 0 has direct access to the hardware. Generally, only the OS and driver have this privilege. Ring3 has the least privilege. All programs have the privilege of Ring 3. To protect the computer, some dangerous instructions can only be executed by the OS, preventing malicious software from
        randomly calling hardware resources. For example, if a program needs to enable a camera, the program must request a Ring 0 driver to do that on its behalf. Otherwise, the operation will be rejected.
      - Problem
        
        three alternative techniques
        
        Full virtualization
        
        Full virtualization was first proposed and implemented by VMware. VMM translates the binary code of the VM OS (guest OS) without modifying the VM OS. VMs have high portability and compatibility. However, binary translation causes the performance overhead of VMM.
        
        Modifying the guest OS binary code during running causes large performance loss and increasesthe VMM development complexity. Xen developed the paravirtualization technique, which compensates for the disadvantages of full virtualization
        
        Paravirtualization
        
        f the guest OS can be modified to be able to aware that it is virtualized, the VM OS uses the Hypercall to replace sensitive instructions in the virtualization with the hypervisor layer to implement virtualization. Non-sensitive instructions such as privileged and program instructions are directly executed at the CPU non-privilege level.
        
        Multiple types of guest OSs can run at the same time. Paravirtualization delivers performance similar to that of the original non-virtualized system.
        
        The host OS can be modified only for open-source systems, such as Linux. Non-open-source systems, such as Windows, do not support paravirtualization. In addition, the modified guest OS has poor portability.
        
        Hardware-assisted virtualization
        
        n full virtualization and paravirtualization, the physical hardware does not support virtualization identification by default. If physical CPUs support virtualization and are able to identify sensitive instructions, it will be a revolutionary change to CPU virtualization.
    - - Memory Virtualization
        
        Multiple VMs can run on the same host. A host usually has one or more memory modules. How can memory resources be allocated to multiple VMs properly? Memory virtualization was introduced to address this issue. One problem with memory virtualization is how to allocate memory address space. Generally, a physical host allocates memory address space as follows
        
        The memory address starts from the physical address 0
        
        The memory address space is allocated continuously