Re: [linux-kernel] Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.

On Tue, 2008-01-08 at 21:19 -0800, H. Peter Anvin wrote:
Zachary Amsden wrote:

BTW, it isn't ever safe to pass port 0x80 through to hardware from a
virtual machine; some OSes use port 0x80 as a hardware available scratch
register (I believe Darwin/x86 did/does this during boot).

That's funny, because there is definitely no guarantee that you get back
what you read (well, perhaps there is on Apple.)

According to Phoenix Technologies book "System BIOS for IBM PCs,
Compatibles and EISA Computers, 2nd Edition", the I/O port list gives

port 0080h R/W Extra page register (temporary storage)

Despite looking, I've never seen it documented anywhere else, but I
believe it works on just about every PC platform. Except, apparently,
my laptop.

Zach

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