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If I understood information here correctly, you can currently play with following mitigations. More will surely show up over time.

Value Platform CVE Notes
1 Intel CVE-2017-5715 Disables Spectre Variant 2 mitigation
2 Intel CVE-2017-5754 Disables Meltdown mitigation
8 Intel CVE-2018-3639 Enables Speculative Store Bypass mitigation
64 AMD CVE-2017-5715 Enable Spectre Variant 2 mitigation on AMD

Combinational values that are seen

  • 0 – enable Spectre/Meltdown on Intel
  • 3 = 2 +1¬†– disable Spectre/Meltdown on Intel

By adding bits together, you could create your custom mitigations. For example:

  • 72 = 64+8 enable all mitigations on all platforms.
  • 11 = 8+2+1 enable CVE-2018-3639 but disable CVE-2017-5715 and CVE-2017-5754

I’m not sure if these values would make any sense or work at all but my guess is that they will not crash anything. By observation, i think each mitigation is optional and can be enabled atomatically if hardware/microcode supports it. I don’t have an AMD at hand but someone could try out these homebrew combinations.

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