Well, A20 has been done inside the caches since 486, usually in the TLB.  Nehalem finally killed off A20M.

You're not the only one surprised by this...

Linus Torvalds [off-list ref] wrote:

On Wed, Dec 19, 2012 at 12:22 PM, H. Peter Anvin [off-list ref]
wrote:

quoted

      x86, 8042: Enable A20 using KBC to fix S3 resume on some MSI

laptops

Christ really? What century are we in? There are still machines that
have A20 disabled at all, much less externally? How do they even do
that these days, afaik the CPU caches can't handle the fake aliasing
anyway..

Anyway, pulled, I just wanted to express my surprise..

         Linus

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