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Being able to patch the microcode only solves part of the possible problems a CPU can have. My guess -- and I hope you can confirm it at some point in the futu
by peterfirefly 2y ago
Being able to patch the microcode only solves part of the possible problems a CPU can have.
My guess -- and I hope you can confirm it at some point in the future -- is that more modern CPUs can patch other data structures as well. Perhaps the TLB walker state machine, perhaps some tables involved in computation (like the FDIV table), almost certainly some of the decoder machinery.
How does one make a patchable parallel multi-stage decoder is what I'd really like to know!
- Tuna-Fish 2y agoMostly, you can turn off parts of the CPU (so called chicken bits). They are invaluable for validation, but they have also been frequently used for for fixing broken CPUs. Most recently AMD just recently turned off their loop buffer in Zen4: https://chipsandcheese.com/p/amd-disables-zen-4s-loop-buffer https://chipsandcheese.com/p/amd-disables-zen-4s-loop-buffer