Re: [PATCH] x86/microcode/intel: Panic on partial microcode update

[Chang S. Bae]

On 7/27/2026 2:59 PM, Sohil Mehta wrote:
> What does an authentication failure mean in this context?


The spec has this:

  When set to 1, it indicates that an authentication failure occurred on
  some portion of the MCU after another portion had already been
  committed and the Revision ID had already been updated on the most
  recent write to IA32_BIOS_UPDT_TRIG.

It would be helpful if including some examples, but those appear to fall 
under microcode implementation details as I heard.

> Does that mean unauthenticated microcode components somehow got loaded?
>
> 	or that
>
> Someone attempted to load bogus microcode which was rejected by the
> processor?


First, the SDM describes the legacy behavior in Vol.3A 12.11.7 "Update 
Signature and Verification". In the legacy flow, an invalid or 
unauthenticated patch is rejected _before_ the revision ID is updated. 
So the outcome is effectively binary: either the update succeeds, or it 
is rejected.

The partial-update status introduce a third outcome. Some portion of the 
update has already been committed and (maybe, therefore) the revision ID 
has been updated, but another portion failed. The result is not the 
simple "accepted" or "rejected" state. This thus could be seen as a 
bogus state from this perspective, TBH.

> If it was rejected, then there is no need to panic, right? Just warning
> about the attempt should be enough.


In this new state, the processor may either continue operating or end up 
running with a combination of sub-components that has never been tested. 
Given that, I think one question to ask in the end is whether we trust 
the microcode's own error handling (completely), or not.

Thanks,
Chang