linux-kernel - Re: [PATCH 10/16] x86/mm/pti: Populate valid user pud entries

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Date:   Tue, 16 Jan 2018 22:06:48 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Joerg Roedel <joro@...tes.org>
cc:     Ingo Molnar <mingo@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.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>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>, aliguori@...zon.com,
        daniel.gruss@...k.tugraz.at, hughd@...gle.com, keescook@...gle.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, jroedel@...e.de
Subject: Re: [PATCH 10/16] x86/mm/pti: Populate valid user pud entries

On Tue, 16 Jan 2018, Joerg Roedel wrote:

> From: Joerg Roedel <jroedel@...e.de>
> 
> With PAE paging we don't have PGD and P4D levels in the
> page-table, instead the PUD level is the highest one.
> 
> In PAE page-tables at the top-level most bits we usually set
> with _KERNPG_TABLE are reserved, resulting in a #GP when
> they are loaded by the processor.
> 
> Work around this by populating PUD entries in the user
> page-table only with _PAGE_PRESENT set.
> 
> I am pretty sure there is a cleaner way to do this, but
> until I find it use this #ifdef solution.

Stick somehting like

#define _KERNELPG_TABLE_PUD_ENTRY

into the 32 and 64 bit variants of some relevant header file 

Thanks,

	tglx