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Date: Wed, 23 Sep 2020 10:45:29 +0800 From: Feng Tang <feng.tang@...el.com> To: Arvind Sankar <nivedita@...m.mit.edu> Cc: Borislav Petkov <bp@...en8.de>, Tom Lendacky <thomas.lendacky@....com>, Yazen Ghannam <yazen.ghannam@....com>, Wei Huang <wei.huang2@....com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>, Dave Hansen <dave.hansen@...el.com>, x86@...nel.org, linux-kernel@...r.kernel.org Subject: Re: [RFC PATCH v2] tools/x86: add kcpuid tool to show raw CPU features Hi Arvind, On Tue, Sep 22, 2020 at 06:15:23PM -0400, Arvind Sankar wrote: > On Tue, Sep 22, 2020 at 10:10:24PM +0200, Borislav Petkov wrote: > > + AMD folks. > > > > On Tue, Sep 22, 2020 at 01:27:50PM +0800, Feng Tang wrote: > > > End users frequently want to know what features their processor > > > supports, independent of what the kernel supports. > > > > > > /proc/cpuinfo is great. It is omnipresent and since it is provided by > > > the kernel it is always as up to date as the kernel. But, it could be > > > ambiguous about processor features which can be disabled by the kernel > > > at boot-time or compile-time. > > > > > > There are some user space tools showing more raw features, but they are > > > not bound with kernel, and go with distros. Many end users are still > > > using old distros with new kernels (upgraded by themselves), and may > > > not upgrade the distros only to get a newer tool. > > > > > > So here arise the need for a new tool, which > > > * Shows raw cpu features got from running cpuid > > > * Be easier to obtain updates for compared to existing userspace > > > tooling (perhaps distributed like perf) > > > * Inherits "modern" kernel development process, in contrast to some > > > of the existing userspace cpuid tools which are still being developed > > > without git and distributed in tarballs from non-https sites. > > > * Can produce output consistent with /proc/cpuinfo to make comparison > > > easier. > > Rather than a tool, would additional file(s) in, say, > /sys/devices/system/cpu/cpu<n> be nicer? They could show the raw CPUID > features, one file per leaf or sub-leaf, maybe even along with whether > they were disabled at boot-time. My thought is we already have in-kernel powerful /proc/cpuinfo, while a user space tool could be more flexible for text parsing/layout, and show different info on user's demand/options. > > > * Be in-kernel, could leverage kernel enabling, and even > > > theoretically consume arch/x86/boot/cpustr.h so it could pick up > > > new features directly from one-line X86_FEATURE_* definitions. > > That's arch/x86/include/asm/cpufeatures.h right -- cpustr.h is generated > from that. The table there already has comments which could be extracted > as the one-line description. Thanks for the hint! I found the comments in cpufeatures.h is much better than what I extraced from SDM :), which I should use instead. One other thing as Boris has mentioned, cpu feature is mixture of raw silicon features and kernel software ones. Also, cpufeatures.h only contains shows ont-bit boolean flag, while cpuid has multiple-bits field containing numbers. Thanks, Feng
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