linux-kernel - Re: [PATCH 2/4] x86: Prepare vm86 tasks to handle User-Mode Instruction Prevention

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Date:   Tue, 08 Nov 2016 20:26:54 -0800
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        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>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 2/4] x86: Prepare vm86 tasks to handle User-Mode
 Instruction Prevention

On Tue, 2016-11-08 at 18:00 +0100, Peter Zijlstra wrote:
> > > +       }
> > > +#endif
> > > +
> > 
> > NAK.  If this code is going to exist, it needs to be deeply buried
> in
> > some unlikely if statement that already exists.  There's no good
> > reason to penalize all context switches to support some nonsensical
> > vm86 use case.
> 
> Agreed, now if instead vm86 get to emulate these instructions, this
> all
> magically goes away..

Yes. I agree. I will rework the series and this should not be needed.

Thanks and BR,
Ricardo