Re: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid

From: Fenghua Yu
Date: Mon Feb 04 2019 - 16:15:27 EST

On Mon, Feb 04, 2019 at 11:05:52AM -0800, Dave Hansen wrote:
> On 2/4/19 9:49 AM, Thomas Gleixner wrote:
> > On Fri, 1 Feb 2019, Fenghua Yu wrote:
> >> This option behaves like existing kernel option clearcpuid.
> >
> > No it does NOT. clearcpuid allows to disable things.
> >
> > This allows to enable random CPUID bits without any sanity checking. Not
> > going to happen. We made it clear in the past that functionality needs to
> > be detectable by enumeration. We do quirks for broken crap, but this is
> > just not how it works.
> Hi Thomas,
> I think we are trying persuade you like mentioned here:
> >
> But, we're not being very persuasive because we kinda forgot about the
> "if and only if" condition that you mentioned.

Intel SDM published TODAY does have IA32_CORE_CAPABILITY MSR enumerateion
bit CPUID.0x7.0:EDX[30] now. Please check today's SDM for the bit:

I will add the two patches that enumerate the MSR and #AC for split lock
in the next version.