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

[Arjan van de Ven]

On 2/16/2018 11:43 AM, Linus Torvalds wrote:
> 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?

yeah I would be extremely surprised
> 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").

once you fake to be skylake when you're not, you do that for a reason; normallyt
that reason is that you COULD migrate to a skylake.
(and migration is not supposed to be visble to the guest OS)

and at that point you are a skylake for all intents and purposes.

(and the virtualization people also really hate it when the hardware
burst the bubble of this fakeing hardware to be not what it is)