linux-kernel - Re: [PATCH 3/3] mm,generic: only flush the local TLB in ptep_set_access

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Date:	Fri, 26 Oct 2012 14:57:51 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...nel.org>, Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/3] mm,generic: only flush the local TLB in ptep_set_access_flags

On 10/26/2012 02:48 PM, Linus Torvalds wrote:
> On Fri, Oct 26, 2012 at 11:46 AM, Rik van Riel <riel@...hat.com> wrote:
>>
>> The function ptep_set_access_flags is only ever used to upgrade
>> access permissions to a page.
>
> NOTE: It's *not* "access permissions". It's "access flags".
>
> Big difference. This is not about permissions at all.

It looks like do_wp_page also sets the write bit in the pte
"entry" before passing it to ptep_set_access_flags, making
that the place where the write bit is set in the pte.

Is this a bug in do_wp_page?

Am I reading things wrong?

reuse:
                 flush_cache_page(vma, address, pte_pfn(orig_pte));
                 entry = pte_mkyoung(orig_pte);
                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                 if (ptep_set_access_flags(vma, address, page_table, 
entry,1))
                         update_mmu_cache(vma, address, page_table);

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