AMD: Updated microcode for Zen 1 to Zen 3

Surprisingly, AMD has released fresh microcode for the Zen 1 through Zen 3 processors. Because there is no changelog, it is impossible to make a definitive statement regarding the content, however, the microcode for older CPUs has been significantly expanded. More about this can be found further down.

The "machine language" used to manage a processor's arithmetic units is microcode from processor makers such as AMD or Intel, and it should be updated on a regular basis to avoid security flaws such as Specter or Meltdown. Microcode updates are often created and released primarily for current-generation products, as these benefit the most from the optimizations.

However, AMD has now released new microcode that is not just built for Zen 3 processors, but also for Zen 1 and Zen 2 processors. However, there is no visible changelog, as is nearly often the case when microcode is released, thus it is unclear what changes the new code will offer.

However, the code itself reveals that, in addition to the 19h family (Zen3), the 17h family (Zen/Zen+/Zen2) has received an update this time, although this had previously only applied to the 19h. The previous update for 17h occurred in December 2019.

Aside from the unexpected inclusion of older chips, the update is also rather hefty. It expands the 17h family microcode to 9,700 bytes from 6,476 bytes previously but leaves the 19h family code unchanged.

However, without an official comment from AMD, one can only assume about the microcode's composition. There are two most likely scenarios.

Since the last upgrade was more than two years ago, AMD could have integrated regular enhancements and minor updates and is now sharing them in microcode, or security flaws that AMD did not wish to leave even with older chips have been patched.