| 1 | <?xml version='1.0' encoding='UTF-8'?>
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| 2 | <!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 3 | <topic xml:lang="en-us" id="hwvirt">
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| 4 | <title>Hardware Virtualization</title>
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| 5 |
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| 6 | <body>
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| 7 | <p>
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| 8 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> enables software in the virtual machine to run
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| 9 | directly on the processor of the host, but an array of complex
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| 10 | techniques is employed to intercept operations that would
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| 11 | interfere with your host. Whenever the guest attempts to do
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| 12 | something that could be harmful to your computer and its data,
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| 13 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> steps in and takes action. In particular, for lots
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| 14 | of hardware that the guest believes to be accessing,
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| 15 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> simulates a certain <i>virtual</i>
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| 16 | environment according to how you have configured a virtual
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| 17 | machine. For example, when the guest attempts to access a hard
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| 18 | disk, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> redirects these requests to whatever you have
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| 19 | configured to be the virtual machine's virtual hard disk. This is
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| 20 | normally an image file on your host.
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| 21 | </p>
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| 22 | <p>
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| 23 | Unfortunately, the x86 platform was never designed to be
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| 24 | virtualized. Detecting situations in which <ph conkeyref="vbox-conkeyref-phrases/product-name"/> needs to
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| 25 | take control over the guest code that is executing, as described
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| 26 | above, is difficult. To achieve this, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> uses
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| 27 | <i>hardware virtualization</i>.
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| 28 | </p>
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| 29 | <p>
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| 30 | Intel and AMD processors have support for hardware virtualization.
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| 31 | This means that these processors can help <ph conkeyref="vbox-conkeyref-phrases/product-name"/> to
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| 32 | intercept potentially dangerous operations that a guest operating
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| 33 | system may be attempting and also makes it easier to present
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| 34 | virtual hardware to a virtual machine.
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| 35 | </p>
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| 36 | <p>
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| 37 | These hardware features differ between Intel and AMD processors.
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| 38 | Intel named its technology VT-x, AMD calls theirs AMD-V. The Intel
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| 39 | and AMD support for virtualization is very different in detail,
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| 40 | but not very different in principle.
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| 41 | </p>
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| 42 | <note>
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| 43 | <p>
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| 44 | On many systems, the hardware virtualization features first need
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| 45 | to be enabled in the BIOS before <ph conkeyref="vbox-conkeyref-phrases/product-name"/> can use them.
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| 46 | </p>
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| 47 | </note>
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| 48 | <p>
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| 49 | Enabling hardware virtualization is <i>required</i>
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| 50 | in the following scenarios:
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| 51 | </p>
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| 52 | <ul>
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| 53 | <li>
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| 54 | <p>
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| 55 | Certain rare guest operating systems like OS/2 make use of
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| 56 | very esoteric processor instructions. For virtual machines
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| 57 | that are configured to use such an operating system, hardware
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| 58 | virtualization is enabled automatically.
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| 59 | </p>
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| 60 | </li>
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| 61 | <li>
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| 62 | <p>
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| 63 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/>'s 64-bit guest and multiprocessing (SMP)
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| 64 | support both require hardware virtualization to be enabled.
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| 65 | This is not much of a limitation since the vast majority of
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| 66 | 64-bit and multicore CPUs ship with hardware virtualization.
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| 67 | The exceptions to this rule are some legacy Intel and AMD
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| 68 | CPUs.
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| 69 | </p>
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| 70 | </li>
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| 71 | </ul>
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| 72 | <note type="caution">
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| 73 | <p>
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| 74 | Do not run other hypervisors, either open source or commercial
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| 75 | virtualization products, together with <ph conkeyref="vbox-conkeyref-phrases/product-name"/>. While
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| 76 | several hypervisors can normally be
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| 77 | <i>installed</i> in parallel, do not attempt to
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| 78 | <i>run</i> several virtual machines from competing
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| 79 | hypervisors at the same time. <ph conkeyref="vbox-conkeyref-phrases/product-name"/> cannot track what
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| 80 | another hypervisor is currently attempting to do on the same
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| 81 | host, and especially if several products attempt to use hardware
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| 82 | virtualization features such as VT-x, this can crash the entire
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| 83 | host.
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| 84 | </p>
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| 85 | </note>
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| 86 | <p>
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| 87 | See <xref href="hwvirt-details.dita#hwvirt-details"/> for a technical discussion of
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| 88 | hardware virtualization.
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| 89 | </p>
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| 90 | </body>
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| 91 |
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| 92 | </topic>
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