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Subject: Re: [tip:x86/asm] x86/umip: Add emulation code for UMIP instructions
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, Peter Anvin <hpa@zytor.com>,
        Borislav Petkov <bp@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        Tony Luck <tony.luck@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Brian Gerst <brgerst@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        ricardo.neri-calderon@linux.intel.com,
        Chris Metcalf <cmetcalf@mellanox.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Andrew Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>, ray.huang@amd.com,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Chen Yucong <slaoub@gmail.com>, Ingo Molnar <mingo@kernel.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
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        <linux-tip-commits@vger.kernel.org>
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From:   Denys Vlasenko <dvlasenk@redhat.com>
Message-ID: <68c11f7a-cd26-0fdc-0ac5-939a72c22227@redhat.com>
Date:   Wed, 8 Nov 2017 18:09:29 +0100
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On 11/08/2017 05:57 PM, Linus Torvalds wrote:
> On Wed, Nov 8, 2017 at 8:53 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
>> We can postpone enabling UMIP by default by a year or so.
>> By this time, new Wine will be on majority of users' machines.
> 
> So you are suggesting we run unnecessarily insecure, only in order to
> not do the emulation that we already have the code for and that the
> patch implements?

We ran insecure in this way for ~25 years.

> Why?

To avoid having to maintain more obscure, rarely executed code.

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