Re: Candidate Linux ABI for Intel AMX and hypothetical new related features

On Wed, Mar 31, 2021 at 5:42 PM Robert O'Callahan [off-list ref] wrote:

For the record, the benefits of dynamic XCR0 for rr recording
portability still apply. I guess it'd be useful for CRIU too. We would
also benefit from anything that incentivizes increased support for
CPUID faulting.

As previously mentioned, today we don't have an architectural way to
trap a user into the kernel on CPUID,
even though we can do this for a VMM.

But spoofing CPUID isn't a solution to all problems.
The feature really needs to be OFF to prevent users from using it,
even if the supported mechanisms of discovering that feature say "NOT PRESENT".

Today there are plenty of users who will opportunistically try everything
in the cloud and choose the machine that allows them to do something
that other machines will not -- even if it is not officially supported.

If something is not enumerated, it really needs to also be turned off.

cheers,
--Len Brown, Intel Open Source Technology Center