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

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Date:   Tue, 1 Nov 2016 15:48:50 +0800
From:   He Chen <he.chen@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>, "Luc, Piotr" <Piotr.Luc@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "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 Mon, Oct 31, 2016 at 12:41:32PM +0100, Paolo Bonzini wrote:
> 
> 
> On 31/10/2016 12:05, Borislav Petkov wrote:
> > On Mon, Oct 31, 2016 at 11:47:48AM +0100, Paolo Bonzini wrote:
> >> The information is all in arch/x86/kernel/cpu/scattered.c's cpuid_bits
> >> array.  Borislav, would it be okay to export the cpuid_regs enum?
> > 
> > Yeah, and kill the duplicated one in arch/x86/events/intel/pt.c too
> > please, while at it.
> > 
> > I'd still put it all in arch/x86/kernel/cpu/scattered.c so that it is
> > close-by and call it from outside.
> 
> Good.  Chen, are you going to do this?
> 

Sure.

Before sending a patch, let me check if my understanding is right...
I will add a helper in scattered.c like:

unsigned int get_scattered_cpuid_features(unsigned int level,
					unsigned int sub_leaf, enum cpuid_regs reg)
{
	u32 val = 0;
	const struct cpuid_bit *cb;

	for (cb = cpuid_bits; cb->feature; cb++) {

		if (reg == cb->reg &&
			level == cb->level &&
			sub_leaf == cb->sub_leaf &&
			boot_cpu_has(cb->feature))

			val |= cb->bit;
	}

	return val;
}

And, when KVM wants to mask out features, it can be called outside like:

entry->edx &= kvm_cpuid_7_0_edx_x86_features;
entry->edx &= get_scatterd_cpuid_features(7, 0, CR_EDX);

Thanks,
-He