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Date:   Wed, 17 Apr 2019 16:47:28 -0700
From:   Fenghua Yu <>
To:     Thomas Gleixner <>
Cc:     Ingo Molnar <>, Borislav Petkov <>,
        H Peter Anvin <>,
        Paolo Bonzini <>,
        Dave Hansen <>,
        Ashok Raj <>,
        Peter Zijlstra <>,
        Ravi V Shankar <>,
        Xiaoyao Li <>,
        Christopherson Sean J <>,
        Kalle Valo <>,
        Michael Chan <>,
        linux-kernel <>,
        x86 <>,,,
Subject: Re: [PATCH v7 18/21] x86/clearcpuid: Support feature flag string in
 kernel option clearcpuid

On Thu, Apr 18, 2019 at 01:19:41AM +0200, Thomas Gleixner wrote:
> On Wed, 17 Apr 2019, Fenghua Yu wrote:
> > The kernel option clearcpuid currently only takes feature bit which
> > can be changed from kernel to kernel.
> > 
> > Extend clearcpuid to use cap flag string, which is defined in
> > x86_cap_flags[] and won't be changed from kernel to kernel.
> > And user can easily get the cap flag string from /proc/cpuinfo.
> If your machine dies because init triggers #AC then please explain how that
> easily can be read from /proc/cpuinfo and how the sysadmin can figure out
> what the heck he needs to write on the kernel command line.
> The whole 'clearcpuid' thing should have never been merged. It's a pure
> testing/debugging thing. And no, we are not going to proliferate it and
> extend it for dubious value. Quite the contrary, we should simply rip it
> out.

So I can remove the four 'clearcpuid' related patches 0018-0021 in the next
version, right?

> Add a simple 'noac' or whatever command line option, which is documented
> proper and can easily be mapped to a #AC crash during boot.

OK. I will do this.



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