linux-kernel - Re: [RFC PATCH 2/3] x86/cpufeatures: Combine word 11 and 12 into new scattered features word 11

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Message-ID: <20190614142550.GD198207@romley-ivt3.sc.intel.com>
Date:   Fri, 14 Jun 2019 07:25:51 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        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>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH 2/3] x86/cpufeatures: Combine word 11 and 12 into new
 scattered features word 11

On Fri, Jun 14, 2019 at 04:26:11PM +0200, Borislav Petkov wrote:
> On Fri, Jun 14, 2019 at 07:15:20AM -0700, Fenghua Yu wrote:
> > Adding this small patch into patch 0002 will solve the build errors without
> > changing the build checks.
> 
> There's no need for that if you remove the BUILD_BUG_ON checks first.

But without this small patch, CPUID_7_EDX is 17 instead of
NCAPINTS(19)-1=18 in patch 0002. Of course CPUID_7_EDX is 18 correctly
evetually after applying patch 0003 which add the word 12 back.

KVM reports this CPUID_7_EDX is not 18 in bisect (as Sena also pointed
out). I think even native kernel should have some check to report this
error (similar to other checks of NCAPINTS).

Thanks.

-Fenghua