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

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Message-ID: <874m89cu61.fsf@x220.int.ebiederm.org>
Date:	Fri, 01 Jul 2016 09:25:10 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Hansen <dave@...1.net>,
	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

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Thu, Jun 30, 2016 at 9:39 PM, Dave Hansen <dave@...1.net> wrote:
>>
>> I think what you suggest will work if we don't consider A/D in
>> pte_none().  I think there are a bunch of code path where assume that
>> !pte_present() && !pte_none() means swap.
>
> Yeah, we would need to change pte_none() to mask off D/A, but I think
> that might be the only real change needed (other than making sure that
> we don't use the bits in the swap entries, I didn't look at that part
> at all)

It looks like __pte_to_swp_entry also needs to be changed to mask out
those bits when the swap code reads pte entries.  For all of the same
reasons as pte_none.

Eric