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Date:	Tue, 07 Oct 2014 19:14:31 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Dr. David Alan Gilbert" <dgilbert@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Andrea Arcangeli <aarcange@...hat.com>, qemu-devel@...gnu.org,
	KVM list <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Linux API <linux-api@...r.kernel.org>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Dave Hansen <dave@...1.net>, Rik van Riel <riel@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Peter Feiner <pfeiner@...gle.com>,
	Christopher Covington <cov@...eaurora.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Neil Brown <neilb@...e.de>, Mike Hommey <mh@...ndium.org>,
	Taras Glek <tglek@...illa.com>, Jan Kara <jack@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Michel Lespinasse <walken@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Keith Packard <keithp@...thp.com>,
	"Huangpeng (Peter)" <peter.huangpeng@...wei.com>,
	Isaku Yamahata <yamahata@...inux.co.jp>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Stefan Hajnoczi <stefanha@...il.com>,
	Wenchao Xia <wenchaoqemu@...il.com>,
	Andrew Jones <drjones@...hat.com>,
	Juan Quintela <quintela@...hat.com>
Subject: Re: [PATCH 10/17] mm: rmap preparation for remap_anon_pages

Il 07/10/2014 19:07, Dr. David Alan Gilbert ha scritto:
>> > 
>> > So I'd *much* rather have a "write()" style interface (ie _copying_
>> > bytes from user space into a newly allocated page that gets mapped)
>> > than a "remap page" style interface
> Something like that might work for the postcopy case; it doesn't work
> for some of the other uses that need to stop a page being changed by the
> guest, but then need to somehow get a copy of that page internally to QEMU,
> and perhaps provide it back later.

I cannot parse this.  Which uses do you have in mind?  Is it for
QEMU-specific or is it for other applications of userfaults?

As long as the page is atomically mapped, I'm not sure what the
difference from remap_anon_pages are (as far as the destination page is
concerned).  Are you thinking of having userfaults enabled on the source
as well?

Paolo

> remap_anon_pages worked for those cases
> as well; I can't think of another current way of doing it in userspace.

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