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

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Message-ID: <b3e6472fba2f4c5494dddc3ac48aba9b@AcuMS.aculab.com>
Date:   Mon, 15 Oct 2018 13:29:34 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jan Kiszka' <jan.kiszka@...mens.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

From: Jan Kiszka
> 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.

I think you missed the :-)
I don't think linux uses that term very often.

Any guesses as to what type DWORD_PTR is?
(in a well know 64bit environment that uses UPPER_CASE for types).

	David

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