linux-kernel - Re: [PATCH 07/34] x86/entry/32: Restore segments before int registers

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Date:   Tue, 6 Mar 2018 08:04:37 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Brian Gerst <brgerst@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jürgen 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>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg Kroah-Hartman <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>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 07/34] x86/entry/32: Restore segments before int registers


* H. Peter Anvin <hpa@...or.com> wrote:

> On NX-enabled hardware NX works with PDE, but the PDPDT in general doesn't
> have permission bits (it's really more of a set of four CR3s than a page
> table level.)

The 4 PDPDT entries are also shadowed in the CPU and are only refreshed
on CR3 loads, not spontaneously reloaded from memory during TLB walk
like regular page table entries, right?

This too strengthens the notion that the third page table level of PAE is more 
like a special in-memory CR3[4] array.

Thanks,

	Ingo