[MODERATED] Re: [PATCH v2 2/8] MDSv2 1

[Andi Kleen <ak@linux.intel.com>]

> - altinstructions are probably not what we want at all for any of these
> mitigations.
> 
> If you have a patched kernel but old microcode and then do a late load
> of the microcode, you have already thrown away the alternatives by that
> point and you'll show as being mitigated but in fact have nops all over
> the place.  A static branch would solve this.

Nothing else in the Linux kernel handles changed CPUIDs from
a microcode load. The microcode loader even detects this case
and warns about it.

The assumption was that if you update the kernel you also update
the microcode, and you do it at boot.

If you do hot update, you are unlikely to have the new patched
kernel anyways, and if you try to hot patch the hooks in too
you can handle it in your patch.

But I don't see any point in complicating the upstream kernel
for such hotpatch only scenarios.

-Andi