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Intel released an update to the Meltdown and Spectre mitigation guide, revealing that it stopped working on mitigations for some processor series.

The Meltdown and Spectre mitigation guide is a PDF document that Intel published in February. The file contains information on the status of microcode updates for each of Intel's CPU models released in the past years.

The file is meant for both end users and OEMs alike, and is intended to help affected users understand what microcode patch they need, and if their OEM has delivered the patch after Intel published the update.

Intel has constantly updated the document in the past weeks with new information about processor series and the microcode firmware version number that includes patches for the Meltdown and Spectre flaws.

List of CPU models that won't receive microcode updates

An update published on Monday includes for the first time a "Stopped" production status. Intel says that processors with a "Stopped" status will not receive microcode updates.

After a comprehensive investigation of the microarchitectures and microcode capabilities for these products, Intel has determined to not release microcode updates for these products for one or more reasons including, but not limited to the following:

•  Micro-architectural characteristics that preclude a practical implementation of features mitigating Variant 2 (CVE-2017-5715).
•  Limited Commercially Available System Software support.
•  Based on customer inputs, most of these products are implemented as “closed systems” and therefore are expected to have a lower likelihood of exposure to these vulnerabilities.

The reasons basically vary from "redesigning the CPU micro-architecture is impossible or not worth the effort" to "it's an old CPU" and "customers said they don't need it."

Reviewing the document, we see that the following Intel processor products received a "Stopped" status marker:

Bloomfield, Bloomfield Xeon, Clarksfield, Gulftown, Harpertown Xeon C0, Harpertown Xeon E0, Jasper Forest, Penryn/QC, SoFIA 3GR, Wolfdale C0, Wolfdale M0, Wolfdale E0, Wolfdale R0, Wolfdale Xeon C0, Wolfdale Xeon E0, Yorkfield, and Yorkfield Xeon.

A quick Google search reveals that most of these are old CPU models, some going back more than a decade, hence, there won't be that many users left to complain about not receiving updates.

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