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

[Brian Gerst]

On Mon, Aug 22, 2016 at 6:23 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On August 22, 2016 2:48:46 PM PDT, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
>>Josh Poimboeuf <jpoimboe@xxxxxxxxxx> 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.

It was added in commit 9cf4f298e29abba25c16679fe7be70898223167e,
copied from 32-bit but never used.  It doesn't look like we ever used
LSS on 64-bit.

--
Brian Gerst