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Thu, 27 Feb 2025 20:14:44 +0000 Message-ID: <8b174f56-191b-45bd-93ec-4c6444c770a5@intel.com> Date: Thu, 27 Feb 2025 12:14:40 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] x86/cpufeature: Add feature dependency checks To: Ingo Molnar CC: , Borislav Petkov , Dave Hansen , Ingo Molnar , "Thomas Gleixner" , "H . 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>> + const struct cpuid_dep *d; >> + >> + for (d = cpuid_deps; d->feature; d++) { >> + if (cpu_has(c, d->feature) && !cpu_has(c, d->depends)) { >> + pr_info("CPU%d: Disabling feature %s due to missing feature %s\n", >> + smp_processor_id(), >> + x86_feature_name(d->feature, feature_buf), >> + x86_feature_name(d->depends, depends_buf)); >> + do_clear_cpu_cap(c, d->feature); >> + } >> + } > > So let's not disable any CPU features actively for the time being, how > about issuing a pr_warn() only about the dependency violation? > > I think the main problem is when these problems slip through 100% > unnoticed. > I guess you are right. Highlighting the issue is the main part. Beyond that we can leave the system behavior as-is for now. Most of the listed dependencies seem to be spec-driven, though the kernel might create arbitrary dependencies for security reasons such as making LAM depend on LASS[1]. I think those can probably be handled on a case by case basis during specific feature enabling. For the new pr_warn(), I am considering printing it only once per feature instead of printing it on every CPU (which could be 100s). But that would mean tracking it in a global feature_warn bitmap. DECLARE_BITMAP(feature_warn, MAX_FEATURE_BITS); Another option would be run the scan only on the BSP. But that could cause some issues to be missed[2]. I am wondering if there is a better way to do this? -Sohil [1]: https://lore.kernel.org/all/20241028160917.1380714-15-alexander.shishkin@linux.intel.com/ [2]: https://lore.kernel.org/lkml/ZsfJUT0AWFhoONWf@google.com/#:~:text=divergent%20features%20from%20the%20boot%20CPU