The Linux kernel is advancing its support for modern processor architectures, with version 7.3 incorporating significant updates related to CPU core identification and management. Key enhancements include the official recognition of a new low-power core type from AMD and a major overhaul to unify how the kernel handles diverse CPU core types from both Intel and AMD.
AMD Low-Power Core Integration and Core Type Standardization
Linux 7.3 now includes an AMD patch that introduces support for a new “low power” CPU core type. This core is intended to complement AMD’s existing lineup of “performance” and “efficiency” cores, similar to those found in Zen 4C/5C architectures. The low-power core is anticipated for use in future Zen 6 clients.
The integration of this new core type is reflected in the merge of the `x86/cpu` pull request for the Linux 7.3 merge window. Specifically, the addition of `AMD_CPU_TYPE_LOW_POWER` allows the kernel to correctly identify this upcoming core, preventing it from being classified as an unknown type.
Beyond this AMD-specific update, the kernel dramatically improves CPU core type handling by implementing a unified system. This standardized approach maps various vendor-specific core types to generic CPU core definitions. This standardization was prompted by the Sashiko AI bot, which identified confusion stemming from differing numerical representations of core types across various vendors.
Further x86 Kernel Optimizations
In addition to the core type standardization, the Linux 7.3 release incorporates several other significant changes within the `x86/core` files. These updates focus on improving compatibility and modernizing kernel interfaces.
Among the core enhancements is a minor optimization targeting older AMD Athlon XP systems. This improvement utilizes the `SFENCE` instruction within the kernel code’s write memory barrier, specifically for CPUs that support SSE but lack SSE2 support. The same pull request also includes a Kernel Control Flow Integrity (KCFI) optimization designed to benefit older Intel CPUs.
Another notable change involves Model Specific Registers (MSRs). The kernel updates have been implemented to transition away from using 32-bit MSR interfaces and toward 64-bit interfaces to simplify the underlying code structure. Developers anticipate that the support for 32-bit model specific register interfaces will be phased out during the Linux 7.4 cycle.
