Re: [PATCH v3] x86/microcode/intel: Reject problematic loading on Granite Rapids systems

[Andrew Cooper]

On 17/09/2026 11:14 am, David Laight wrote:
> On Wed, 16 Sep 2026 22:59:39 +0000
> "Chang S. Bae" <chang.seok.bae@xxxxxxxxx> wrote:
>
>> Microcode updates can usually jump revisions. However, there is an
>> erratum on Granite Rapids systems. If they "jump over" revision
>> 0x1000405, they result in #MC. Avoid it.
> A probably silly question.
> Is it valid to downgrade microcode?

Yes, and it does happen in practice.

Intel microcode contains a field called the Security Version Number. 
The SVN bumps as infrequently as possible, but does bump when necessary.

There is a hard block on the SVN going backwards, but as long as you're
not violating this constraint, you can upgrade or downgrade microcode as
desired.

~Andrew