Re: [RFC][PATCH] x86: proposed new ARCH_CAPABILITIES MSR bit for RSB-underflow

[Linus Torvalds]

On Fri, Feb 16, 2018 at 11:38 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> Of course, your patch still doesn't allow for "we claim to be skylake
> for various other independent reasons, but the RSB issue is fixed".

.. maybe nobody ever has a reason to do that, though?

Who knows, virtualization people may simply want the user to specify
the model, but then make the Spectre decisions be based on actual
hardware capabilities (whether those are "current" or "some minimum
base").

Two bits allow that. One bit means "if you claim you're running
skylake, we'll always have to stuff, whether you _really_ are or not".

                   Linus