Re: Boot code awareness of the Hypervisor extension

Greg Favor

On Wed, Jun 24, 2020 at 1:36 PM Andrew Waterman <andrew@...> wrote:
If so, that might be along the lines of saying that an implementation that supports a new architecture extension is not required to be able to run "old/legacy" M-mode boot software that is unaware of the possible existence of that extension, and is not required to then run all other extension-unaware system and user software as expected while the extension remains enabled.  Conversely it would be the M-mode boot software's responsibility to properly either disable a new extension, or initialize the extension's relevant architectural state so that other (well-behaved) extension-unaware system and user software can run as expected.

I think it's the kind of thing that belongs in the FAQ that Mark mentioned in his previous email.

It seems like Mark's FAQ suggestion was more general and different from his specific "well documented guidance" comment on this particular issue.  To me this particular guidance would belong in the Priv spec so as to make it clear that there is not a hardware requirement to be able to run "old" extension-unaware software all the way from boot onwards.  But I'll leave it to you to judge where this best belongs.


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