Re: [PATCH v4 22/22] x86/fpu/xstate: Introduce boot-parameters to control state component support

[Len Brown]

On Thu, Mar 25, 2021 at 7:10 PM Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
>
> On 3/25/21 3:59 PM, Len Brown wrote:
> > We call AMX a "simple state feature" -- it actually requires NO KERNEL ENABLING
> > above the generic state save/restore to fully support userspace AMX
> > applications.
> >
> > While not all ISA extensions can be simple state features, we do expect
> > future features to share this trait, and so we want to be sure that it is simple
> > to update the kernel to turn those features on (and when necessary, off).
>
> From some IRC chats with Thomaas and Andy, I think it's safe to say that
> they're not comfortable blindly enabling even our "simple features".  I
> think we're going to need at least some additional architecture to get
> us to a point where everyone will be comfortable.

Hi Dave,

There is no code in this patch series, including patch 22, that enables
an unvalidated feature by default.

Yes, I fully accept that patch 22 allows a user to enable something
that a distro didn't validate.

If there is a new requirement that the kernel cmdline not allow anything
that a distro didn't explicitly validate, then about 99.9% of the kernel cmdline
options that exist today would need to be removed.

Does such a requirement exist, or does it not?

thanks,
-Len