linux-kernel - Re: [PATCH 1/4] x86/cpufeature: Add User-Mode Instruction Prevention definitions

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Date:   Wed, 09 Nov 2016 19:24:43 -0800
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>, Brian Gerst <brgerst@...il.com>,
        Chen Yucong <slaoub@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 1/4] x86/cpufeature: Add User-Mode Instruction
 Prevention definitions

On Wed, 2016-11-09 at 03:02 -0800, Andy Lutomirski wrote:
> On Tue, Nov 8, 2016 at 8:25 PM, Ricardo Neri
> <ricardo.neri-calderon@...ux.intel.com> wrote:
> > On Tue, 2016-11-08 at 07:32 -0800, Andy Lutomirski wrote:
> >> > diff --git a/arch/x86/include/asm/disabled-features.h
> >> b/arch/x86/include/asm/disabled-features.h
> >> > index 85599ad..4707445 100644
> >> > --- a/arch/x86/include/asm/disabled-features.h
> >> > +++ b/arch/x86/include/asm/disabled-features.h
> >> > @@ -16,6 +16,12 @@
> >> >  # define DISABLE_MPX   (1<<(X86_FEATURE_MPX & 31))
> >> >  #endif
> >> >
> >> > +#ifdef CONFIG_X86_INTEL_UMIP
> >>
> >> ^^^^^
> >>
> >> What's this?
> >>
> >> Let's try to do this with a minimum of configuration.
> >
> > My intention here is put in this file all the #if build configurations
> > so that I don't have to put them other files by using functions such as
> > cpu_feature_enable. Isn't this the intention of this file?
> 
> What I mean is: why does this need a config option at all?

I intended this feature to be configurable at build time in case someone
wants to build a kernel without it; similar to other features such as
SMAP. Is this not needed? Should Linux be built with this feature always
enabled?

This feature could always be disabled via a kernel parameter, though;
even if Linux is built with it.

Thanks and BR,
Ricardo
> 
> --Andy