Within the every increasingly complex world of CPU security mitigations, Intel engineers have submitted Linux kernel patches to begin taking into account the CPU core "hybrid" topology when determining relevant CPU security vulnerabilities and in turn the mitigations to apply.

The patches sent out this Monday morning from Intel are adding the CPU-type information to the kernel's x86/x86_64 topology code. The immediate use case of properly reporting through the CPU type as part of the processor topology is in the handling of CPU vulnerabilities.

Some of the CPU security vulnerabilities are applied on the basis of matching the CPU family / model / stepping IDs. But with current Intel ID practices, the model/stepping ID is often shared among many processors SKUs including some with different combinations of P and E cores -- or with some SKUs no E cores at all. Like with the [1]Intel Core i3 14100 there are four P cores but no E cores at all.

So with the current x86_64 CPU vulnerability/mitigation handling, even these P-core-only SKUs may end up seeing mitigations applied that are only relevant for systems having E cores. The immediate difference with these new Linux kernel patches is that the P-core-only processors will no longer see [2]Register File Data Sampling (RFDS) mitigation applied with [3]RFDS only being needed for E-core / Atom processor cores. Now the mitigation code is "smart" enough to account for the core type topology.

Presumably with time there will be more uses for having this CPU-type information available from within the kernel's processor topology code. [4]These patches are now out for review in their way toward the mainline kernel.



[1] https://www.phoronix.com/review/intel-14100-14500-amd-ryzen

[2] https://www.phoronix.com/review/intel-rfds-performance

[3] https://www.phoronix.com/search/RFDS

[4] https://lore.kernel.org/linux-pm/20240617-add-cpu-type-v1-0-b88998c01e76@linux.intel.com/