These techniques incur some performance overhead due to lack of MMU virtualization support, as compared to a VM running on a natively virtualizable architecture such as the IBM System/370. I/O device emulation: Unsupported devices on the guest OS must be emulated by a device emulator that runs in the host OS.Shadow descriptor tables must therefore be used to track changes made to the descriptor tables by the guest OS. The x86 architecture uses hidden state to store segment descriptors in the processor, so once the segment descriptors have been loaded into the processor, the memory from which they have been loaded may be overwritten and there is no way to get the descriptors back from the processor. : 5 : 2 This involves denying the guest OS any access to the actual page table entries by trapping access attempts and emulating them instead in software. Because most operating systems use paged virtual memory, and granting the guest OS direct access to the MMU would mean loss of control by the virtualization manager, some of the work of the x86 MMU needs to be duplicated in software for the guest OS using a technique known as shadow page tables. A number of key data structures used by a processor need to be shadowed.: 1 To improve performance, the translated basic blocks need to be cached in a coherent way that detects code patching (used in VxDs for instance), the reuse of pages by the guest OS, or even self-modifying code. Binary translation is used to rewrite in terms of ring 3 instructions certain ring 0 instructions, such as POPF, that would otherwise fail silently or behave differently when executed above ring 0, : 3 making the classic trap-and-emulate virtualization impossible.Three techniques made virtualization of protected mode possible: One approach used in x86 software-based virtualization to overcome this limitation is called ring deprivileging, which involves running the guest OS at a ring higher (lesser privileged) than 0. In software-based virtualization, a host OS has direct access to hardware while the guest OSs have limited access to hardware, just like any other application of the host OS. In protected mode the operating system kernel runs at a higher privilege such as ring 0, and applications at a lower privilege such as ring 3. The following discussion focuses only on virtualization of the x86 architecture protected mode. 2.3.2.1 PCI-SIG Single Root I/O Virtualization (SR-IOV).2.3.1 I/O MMU virtualization (AMD-Vi and Intel VT-d).2.1.5 Interrupt virtualization (AMD AVIC and Intel APICv).However, I will leave this answer here for others searching for it. As per the updated question, the Atmel AT91SAM9 seems to not have this functionality. Not all ARM SoCs support this functionality. It is also known that the reading can fail when u-boot is not properly configured. In the raspberry this number is generally used as a SN to buy a video codec license. And sometimes either software or configurations fail.įew use cases for the SID are, but not limited to: Getting Your Raspberry Pi Serial Number Using PythonĪbout this serial number : It is supposed to be unique, but it is read differently on different SoCs. (taken from my H3 based Soc, Orange Pi One with Armbian/Jessie kernel 3.4) (taken from my A20 based SoC, Lamobo R1 aka Banana Pi R1 and ArmBian/Jessie with kernel 4.5.2) grep Serial /proc/cpuinfo Get the serial of the device from /proc/cpuinfo grep Serial /proc/cpuinfo
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