linux-kernel - Re: [RFC PATCH] x86/cpufeatures: Enumerate new AVX512 bfloat16 instructions

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Message-ID: <20190612040259.GC32652@zn.tnic>
Date:   Wed, 12 Jun 2019 06:02:59 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [RFC PATCH] x86/cpufeatures: Enumerate new AVX512 bfloat16
 instructions

On Tue, Jun 11, 2019 at 08:32:59PM -0700, Fenghua Yu wrote:
> Currently KVM doesn't simulate scattered features (the ones in CPUID_LNX_*
> in cpuid_leafs) as reverse_cpuid[] doesn't contain CPUID_LNX_*.

43500e6f294d ("x86/cpufeatures: Remove get_scattered_cpuid_leaf()")

> After the X86_FEATURES_CQM_* features are changed to scattered features,
> they will not be simulated by KVM any more as CPUID_F_0_EDX and CPUID_F_1_EDX
> are removed.

Does KVM even support resctrl? I doubt only exporting a couple of CPUID
bits into the guest is enough...

> Should patch #1 simulate X86_FEATURE_CQM_* in KVM? Or let KVM guys handle
> the scattered features?

Right, the scattered thing was removed as KVM didn't need it,
apparently, see above.

-- 
Regards/Gruss,
    Boris.

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