Intel's Abandoned "Many Integrated Core" Architecture Being Removed With Linux 5.10

Written by Michael Larabel in Intel on 1 November 2020 at 09:06 AM EST. 26 Comments
While Linux 5.10-rc2 is coming later today and a week past the merge window, a notable late pull request sent in this morning by Greg Kroah-Hartman is removing the Intel MIC (Many Integrated Core) architecture drivers, a.k.a. Xeon Phi.

Lightening up the kernel tree by nearly twenty-seven thousand lines of code is the removal of the Intel MIC drivers from the kernel. This is code for Intel's failed Intel MIC X100 (Knights Corner and beyond) that was the PCIe form factor add-in co-processor cards based on their Many Integrated Core architecture and derived from the earlier Larrabee project and more. Running on the accelerator cards themselves were their own Linux build. The drivers being removed from Linux 5.10 is all the code for interfacing with the these accelerators that during their short-lived time were marketed as Xeon Phi.

Intel added the MIC code in 2013 and continued improving it for a short time since. With MIC / Xeon Phi having been abandoned for several years now in favor of their CPU and GPU efforts, the Intel MIC code is being removed starting with Linux 5.10.

The justification is that the devices have been discontinued for years and Intel no longer wants to maintain the code especially with the hardware never shipping at large scales. Years ago Intel Xeon Phi cards were clearing their inventory at crazy low prices.

In today's pull request removing MIC, Greg Kroah-Hartman also noted that security researchers / kernel developers were beginning to see security issues with the MIC driver code, "This is welcomed by many as the DMA usage of these drivers was "interesting" and the security people were starting to question some issues that were starting to be found in the codebase."

Thus for ~27k lines of code for hardware that was never widely deployed, hasn't been sold retail for years, and beginning to see possible security issues crop up with the code: it's time to go. This also happens elsewhere in the kernel too for removing buggy kernel code if it's unmaintained or for less common hardware and no one is willing to step up and properly maintain it.

There is one piece of the MIC code-base might be restored in the future. Greg noted that the VOP (VirtIO over PCIe) might see it reworked for use by other PCI Express devices and added back to the kernel later in the future. The Intel VOP code solves some PCI Express virtualization issues that impact other vendors but at the present time the code is only designed for the Intel hardware/drivers. So if this code is made to work more broadly that VOP portion could see mainline again in the future. VOP allows creating user-space back-ends/devices on the host that are used to probe / interface with VirtIO drivers for the devices/blocks on the PCIe card.

But in any case, today's char/misc fixes is dropping the Intel MIC code for Linux 5.10.
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