linux-kernel - Re: [PATCH] x86/entry/32: Fix setup of CS high bits

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Message-ID: <1246b176-02bf-3c04-5470-69333951263b@siemens.com>
Date:   Mon, 15 Oct 2018 15:18:12 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     David Laight <David.Laight@...LAB.COM>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH] x86/entry/32: Fix setup of CS high bits

On 15.10.18 15:14, David Laight wrote:
> From: Jan Kiszka
>> Sent: 15 October 2018 14:09
> ...
>>> Those fields are genuinely 16 bit.  So the comment should say
>>> something like "Those high bits are used for CS_FROM_ENTRY_STACK and
>>> CS_FROM_USER_CR3".
>>
>> /*
>>    * The high bits of the CS dword (__csh) are used for
>>    * CS_FROM_ENTRY_STACK and CS_FROM_USER_CR3. Clear them in case
>>    * hardware didn't do this for us.
>>    */
> 
> What's a 'dword' ? :-)
> 
> On a 32bit processor a 'word' will be 32 bits to a 'double-word'
> would be 64 bits.
> One of the worst names to use.

That's ia32 nomenclature: a doubleword (dword) is a 32-bit value.

Jan

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