linux-kernel - RE: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid

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Date:   Tue, 12 Feb 2019 17:52:55 +0000
From:   "Yu, Fenghua" <fenghua.yu@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        H Peter Anvin <hpa@...or.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Michael Chan <michael.chan@...adcom.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Neri, Ricardo" <ricardo.neri@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: RE: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid

> From: Peter Zijlstra [mailto:peterz@...radead.org]
> On Tue, Feb 12, 2019 at 02:51:00PM +0100, Thomas Gleixner wrote:
> > On Tue, 12 Feb 2019, Peter Zijlstra wrote:
> >
> > > On Mon, Feb 11, 2019 at 11:16:43AM -0800, Fenghua Yu wrote:
> > > > 4. The feature can be disabled by kernel option
> > > > "clearcpuid=split_lock_detection" during early boot time.
> > >
> > > IFF clearcpuid lives, it should also employ CPUID faulting and clear
> > > it for userspace too.
> >
> > We have it already,
> 
> D'0h right, I thought that was introduced here, but that's just extending it
> to multiple arguments.

In this patch set, patch #5 extends clearcpuid to support multiple options and
Patch #6 extends clearcpuid to support cpu cap flag strings. So we already have
string support and can use "clearcpuid=split_lock_detection" to disable
the split lock feature at the boot time.

Thanks.

-Fenghua