linux-kernel - Re: [PATCH] x86/cpuid: expose AVX512_4VNNIW and AVX512

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Message-ID: <1477905033.32008.5.camel@intel.com>
Date:   Mon, 31 Oct 2016 09:15:43 +0000
From:   "Luc, Piotr" <Piotr.Luc@...el.com>
To:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "he.chen@...ux.intel.com" <he.chen@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Kang, Luwei" <luwei.kang@...el.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>
Subject: Re: [PATCH] x86/cpuid: expose AVX512_4VNNIW and AVX512_4FMAPS
 features to kvm guest

On Sat, 2016-10-29 at 08:21 -0400, Paolo Bonzini wrote:
> 
> Currently none of the bits in CPUID[7,0].edx is ever masked by the
> host, so
> this would be enough.  If we ever need to do some masking, I guess
> I'll
> practice my puss-in-boots look and submit a patch to add CPUID[7,0]
> back
> as a separate cpufeature entr.

I think that in v4.9-rc2 the CPUID[7,0].edx bits can be masked out by
applying noxsave to cmdline. Using directly cpu_count will result in
passing the bits in edx to a guest directly while the xsaveopt and rest
of AVX512 features bits will be cleared. 

Thx
Piotr