Intel hardware Virtual home technology VT-x

Source: http://hi.baidu.com/kiropower/blog/item/5d84f2a81a2111a8ca130c98.html

Intel virtualization technology can be divided into CPU processor VT Technology (Vt-x), chipset VT Technology (Vt-d) and network VT Technology (Vt-C ):

VT-X Technology:

The VT-X Technology in Intel VT is the hardware virtualization technology of the CPU. vt can improve the virtualization efficiency and security of virtual machines at the same time. The VT technology on the X86 platform is generally called VT-X, the VT technology on the itanium platform is called VT-I.

VT-x extends the traditional x86 processor architecture. It introduces two operation modes: vmx root operation (root virtualization operation) and vmx non-root operation (non-root virtualization operation ), it is collectively referred to as the vmx operation mode. Vmx root operation is the mode in which vmm runs and is designed for use by vmm/hypervisor. Its behavior is not particularly different from that of traditional ia32, vmx non-root operation is the mode in which the client runs. It is in the ia32/64 Environment under vmm control. All modes support all four privileges.
Levels.

Therefore, commands such as gdt, IDT, LDT, and TSS can run normally inside the virtual machine. In the past, these privileged commands had to be simulated. Vmm can also be freed from the simulation of running privileged commands, which can solve the ring aliasing problem (the actual running ring of the software is different from the designed running ring ), it can solve the ring compression problem and greatly improve the running efficiency. The solution to the ring compression problem solves the 64-bit operating system operation problem.

to establish these two operating modes, VT-x designs a virtual-machine control structure (vmcs, virtual machine control structure) data structure, it includes the guest-state area and host-state area to save the status parameters of virtual machines and hosts, the VM entry and Vm exit operations are provided to switch between the VM and vmm, in the VM-execution control fields of vmcs, you can specify the command to be executed and the event to be executed, vmx non-root
the virtual machine in the operation environment executes the VM exit to allow the vmm to gain control. Therefore, VT-x solves the Isolation Problem of the Virtual Machine and the performance problem.
EPT and vpid are memory Virtualization Technologies, abbreviated as page table extended page table (EPT), and part of VT-x technology. The main task of memory virtualization is to achieve address space virtualization. Memory virtualization supports address space virtualization through two address conversions, that is, the conversion of the client virtual address GVA-> the physical address GPA-> the physical address HPA of the host. Traditional IA-32 supports only one address translation. Memory virtualization requires two memory conversions. That is, the vmm calculates the "shadow page table" based on the ing relationship of the GVA-GPA-HPA. The disadvantage of the software implementation is the high memory overhead and poor performance. The EPT technology supports two address conversions of the GVA-GPA-HPA directly on the hardware.
vpid is short for virtual processor IDs. It is a hardware-level optimization for TLB resource management. It adds a flag to each TLB item on the hardware, to identify the address space of different virtual processors, separate the vmm and The TLB of different virtual processors of different virtual machines. To implement these functions, VT-x adds some special commands for EPT and vmm, such as invert and invlpg, so it requires software support. Currently, VMWare ESX 4.0 and xen 3.4 support this feature. These memory hardware Virtualization Technologies greatly reduce the difficulty of memory virtualization and improve performance.