linux-kernel - Re: [RFC 3/6] mm: mark dirty bit on swapped-in page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150610072305.GB13008@uranus>
Date:	Wed, 10 Jun 2015 10:23:05 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Yalin Wang <yalin.wang@...ymobile.com>
Subject: Re: [RFC 3/6] mm: mark dirty bit on swapped-in page

On Wed, Jun 10, 2015 at 08:52:06AM +0900, Minchan Kim wrote:
> > > +++ b/mm/memory.c
> > > @@ -2557,9 +2557,11 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
> > >  
> > >  	inc_mm_counter_fast(mm, MM_ANONPAGES);
> > >  	dec_mm_counter_fast(mm, MM_SWAPENTS);
> > > -	pte = mk_pte(page, vma->vm_page_prot);
> > > +
> > > +	/* Mark dirty bit of page table because MADV_FREE relies on it */
> > > +	pte = pte_mkdirty(mk_pte(page, vma->vm_page_prot));
> > >  	if ((flags & FAULT_FLAG_WRITE) && reuse_swap_page(page)) {
> > > -		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
> > > +		pte = maybe_mkwrite(pte, vma);
> > >  		flags &= ~FAULT_FLAG_WRITE;
> > >  		ret |= VM_FAULT_WRITE;
> > >  		exclusive = 1;
> > 
> > Hi Minchan! Really sorry for delay in reply. Look, I don't understand
> > the moment -- if page has fault on read then before the patch the
> > PTE won't carry the dirty flag but now we do set it up unconditionally
> > and to me it looks somehow strange at least because this as well
> > sets soft-dirty bit on pages which were not modified but only swapped
> > out. Am I missing something obvious?
> 
> It's same one I sent a while ago and you said it's okay at that time. ;-)

Ah, I recall. If there is no way to escape dirtifying the page in pte itself
maybe we should at least not make it softdirty on read faults?

> Okay, It might be lack of description compared to one I sent long time ago
> because I moved some part of description to another patch and I didn't Cc
> you. Sorry. I hope below will remind you.
> 
> https://www.mail-archive.com/linux-kernel%40vger.kernel.org/msg857827.html
> 
> In summary, the problem is that in MADV_FREE point of view,
> clean anonymous page(ie, no dirty) in  page table entry has a problem
> about sudden discarding under us by reclaimer. Otherwise, VM cannot
> discard MADV_FREE hinted pages by PageDirty flag of page descriptor.
> 
> This patchset aims for solving the problem.
> Please feel free to ask if you have questions without wasting your time
> unless you can remind after reading above URL
> 
> Thanks for looking!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/