Integrated: 8367780: Enable UseAPX on Intel CPUs only when both APX_F and APX_NCI_NDD_NF cpuid features are present

[Srinivas Vamsi Parasa]

On Tue, 16 Sep 2025 18:04:33 GMT, Srinivas Vamsi Parasa <sparasa at openjdk.org> wrote:

> The goal of this PR is to enable APX on Intel CPUs (i.e. enable UseAPX) only when both the APX_F and APX_NCI_NDD_NF cpuid feature flags are present.
> 
> The latest update to the Intel APX specification (https://www.intel.com/content/www/us/en/content-details/861610/intel-advanced-performance-extensions-intel-apx-architecture-specification.html ) has changed how APX features are detected on Intel CPUs. Because of this change, we need to update how the JVM enumerates CPU features.
> 
> As per the new update, when APX_F is set, processors also provide CPUID leaf 0x29 (APX Advanced Performance Extensions Leaf). Any Intel processor that enumerates APX_F also enumerates APX_NCI_NDD_NF.
> 
> This PR enhances the HotSpot x86 CPU feature detection to recognize the APX_NCI_NDD_NF sub-feature of Intel APX and update the enabling logic for UseAPX VM flag.

This pull request has now been integrated.

Changeset: 3d4e0491
Author:    Srinivas Vamsi Parasa <sparasa at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/3d4e0491940c4b4a05ac84006933d939370e7e2b
Stats:     29 lines in 2 files changed: 26 ins; 0 del; 3 mod

8367780: Enable UseAPX on Intel CPUs only when both APX_F and APX_NCI_NDD_NF cpuid features are present

Reviewed-by: sviswanathan, vpaprotski

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PR: https://git.openjdk.org/jdk/pull/27320