linux-kernel - Re: [PATCH 5/8] x86/head: remove useless zeroed word

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Message-ID: <20F06417-E41D-4B0C-983B-3E8CA55F5AF1@zytor.com>
Date:   Mon, 22 Aug 2016 15:23:30 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Andi Kleen <andi@...stfloor.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH 5/8] x86/head: remove useless zeroed word

On August 22, 2016 2:48:46 PM PDT, Andi Kleen <andi@...stfloor.org> wrote:
>Josh Poimboeuf <jpoimboe@...hat.com> writes:
>
>> This zeroed word has no apparent purpose, so remove it.
>>
>> Brian Gerst says:
>>
>>   "FYI the word used to be the SS segment selector for the LSS
>>   instruction, which isn't needed in 64-bit mode."
>>
>
>Seems dangerous. It wouldn't surprise me if some CPUs or x86 emulations
>load it anyways and trigger page faults if there is really nothing
>there.
>
>-Andi

Yes, seems pointlessly risky.
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