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From: ebiederm@xmission.com (Eric W. Biederman)
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Date: Fri, 01 Jul 2016 09:25:10 -0500
In-Reply-To: <CA+55aFydq3kpT-mzPqcU1_1h=+vSUj6RmQwiz5NVnfY4HfSjXw@mail.gmail.com>
	(Linus Torvalds's message of "Thu, 30 Jun 2016 22:43:09 -0700")
Message-ID: <874m89cu61.fsf@x220.int.ebiederm.org>
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Subject: Re: [PATCH 6/6] x86: Fix stray A/D bit setting into non-present PTEs
Sender: owner-linux-mm@kvack.org
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, the arch/x86 maintainers <x86@kernel.org>, linux-mm <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, Borislav Petkov <bp@alien8.de>, Andi Kleen <ak@linux.intel.com>, Michal Hocko <mhocko@suse.com>, Dave Hansen <dave.hansen@linux.intel.com>

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

> On Thu, Jun 30, 2016 at 9:39 PM, Dave Hansen <dave@sr71.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

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