Linux 7.3 Bringing A KCFI Optimization To Benefit Older Intel CPUs

Linux 7.3 will include a Kernel Control Flow Integrity (KCFI) optimization developed by Intel's Peter Zijlstra, targeting older Intel processors that lack FineIBT/CET with Indirect Branch Tracking (IBT) support — a feature present only in 11th Gen Tiger Lake and newer CPUs. The patch replaces a branch sequence where the Jcc is always taken (suboptimal throughput) with an alternative sequence using a UDB instruction embedded as an immediate byte in a test instruction, improving branch prediction efficiency. The patch is queued in tip/tip.git's x86/core branch and is expected to be submitted during the Linux 7.3 merge window.

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