92 lines
4.2 KiB
XML
92 lines
4.2 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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<topic xml:lang="en-us" id="hwvirt">
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<title>Hardware Virtualization</title>
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<body>
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<p>
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<ph conkeyref="vbox-conkeyref-phrases/product-name"/> enables software in the virtual machine to run
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directly on the processor of the host, but an array of complex
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techniques is employed to intercept operations that would
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interfere with your host. Whenever the guest attempts to do
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something that could be harmful to your computer and its data,
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<ph conkeyref="vbox-conkeyref-phrases/product-name"/> steps in and takes action. In particular, for lots
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of hardware that the guest believes to be accessing,
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<ph conkeyref="vbox-conkeyref-phrases/product-name"/> simulates a certain <i>virtual</i>
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environment according to how you have configured a virtual
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machine. For example, when the guest attempts to access a hard
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disk, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> redirects these requests to whatever you have
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configured to be the virtual machine's virtual hard disk. This is
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normally an image file on your host.
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</p>
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<p>
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Unfortunately, the x86 platform was never designed to be
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virtualized. Detecting situations in which <ph conkeyref="vbox-conkeyref-phrases/product-name"/> needs to
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take control over the guest code that is executing, as described
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above, is difficult. To achieve this, <ph conkeyref="vbox-conkeyref-phrases/product-name"/> uses
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<i>hardware virtualization</i>.
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</p>
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<p>
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Intel and AMD processors have support for hardware virtualization.
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This means that these processors can help <ph conkeyref="vbox-conkeyref-phrases/product-name"/> to
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intercept potentially dangerous operations that a guest operating
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system may be attempting and also makes it easier to present
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virtual hardware to a virtual machine.
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</p>
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<p>
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These hardware features differ between Intel and AMD processors.
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Intel named its technology VT-x, AMD calls theirs AMD-V. The Intel
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and AMD support for virtualization is very different in detail,
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but not very different in principle.
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</p>
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<note>
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<p>
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On many systems, the hardware virtualization features first need
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to be enabled in the BIOS before <ph conkeyref="vbox-conkeyref-phrases/product-name"/> can use them.
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</p>
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</note>
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<p>
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Enabling hardware virtualization is <i>required</i>
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in the following scenarios:
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</p>
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<ul>
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<li>
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<p>
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Certain rare guest operating systems like OS/2 make use of
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very esoteric processor instructions. For virtual machines
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that are configured to use such an operating system, hardware
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virtualization is enabled automatically.
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</p>
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</li>
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<li>
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<p>
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<ph conkeyref="vbox-conkeyref-phrases/product-name"/>'s 64-bit guest and multiprocessing (SMP)
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support both require hardware virtualization to be enabled.
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This is not much of a limitation since the vast majority of
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64-bit and multicore CPUs ship with hardware virtualization.
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The exceptions to this rule are some legacy Intel and AMD
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CPUs.
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</p>
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</li>
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</ul>
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<note type="caution">
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<p>
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Do not run other hypervisors, either open source or commercial
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virtualization products, together with <ph conkeyref="vbox-conkeyref-phrases/product-name"/>. While
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several hypervisors can normally be
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<i>installed</i> in parallel, do not attempt to
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<i>run</i> several virtual machines from competing
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hypervisors at the same time. <ph conkeyref="vbox-conkeyref-phrases/product-name"/> cannot track what
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another hypervisor is currently attempting to do on the same
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host, and especially if several products attempt to use hardware
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virtualization features such as VT-x, this can crash the entire
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host.
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</p>
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</note>
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<p>
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See <xref href="hwvirt-details.dita#hwvirt-details"/> for a technical discussion of
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hardware virtualization.
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</p>
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</body>
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</topic>
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