linux-kernel - Re: [PATCH 6/6] x86: Fix stray A/D bit setting into non-present PTEs

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Date:	Sun, 3 Jul 2016 10:10:39 -0700
From:	Dave Hansen <dave@...1.net>
To:	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andi Kleen <ak@...ux.intel.com>,
	Michal Hocko <mhocko@...e.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 6/6] x86: Fix stray A/D bit setting into non-present PTEs

On 06/30/2016 08:06 PM, Brian Gerst wrote:
>> > It's not like anybody will ever care about 32-bit page tables on
>> > Knights Landing anyway.
> Could this affect a 32-bit guest VM?

This isn't about 32-bit *mode*.  It's about using the the 32-bit 2-level
_paging_ mode that supports only 4GB virtual and 4GB physical addresses.
 That mode also doesn't support the No-eXecute (NX) bit, which basically
everyone needs today for its security benefits.

Even the little Quark CPU supports PAE (64-bit page tables).