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I have an HP desktop, and I wanted to install VirtualBox, so I could run an XP VM (gotta test stuff in IE8).

Before setting this up, I went into my BIOS to check if Hardware Virtualization was on. I found the setting in the BIOS, and there was a note about it.

HP recommends keeping this setting off unless you need it

I'm paraphrasing, I forget the exact note.

I do need it, so I turned it on, but I was curious. Why does HP recommend that? What harm could come from having Hardware Virtualization on if you're not using it (to run VMs)?

Hennes
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gen_Eric
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2 Answers2

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There are several attack vectors from bad drivers that can utilize VT extensions to do potentially bad things. that's why the setting is usually in the "security" section of your BIOS UI.

additionally the smaller your instruction set, the more efficient the CPU runs at a very very low level (hence last decades interest in RISC chips). having it disabled allows the CPU to cache fewer instructions and search the cache faster.

http://en.wikipedia.org/wiki/Blue_Pill_%28software%29

Frank Thomas
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another reason is most user kernel function are moved in VDSO (like gettimeofday).

sometimes under virtualization this fast path cannot be enabled.

so the system cannot:

gain the fast execution of these functions

avoid expensive switch from userland to kernel and return

Community
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Massimo
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