linux-kernel - Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

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Message-ID: <20080130000559.GB7233@v2.random>
Date:	Wed, 30 Jan 2008 01:05:59 +0100
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Robin Holt <holt@....com>, Avi Kivity <avi@...ranet.com>,
	Izik Eidus <izike@...ranet.com>, Nick Piggin <npiggin@...e.de>,
	kvm-devel@...ts.sourceforge.net,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address
	ranges

On Wed, Jan 30, 2008 at 01:00:39AM +0100, Andrea Arcangeli wrote:
> get_user_pages, regular linux writes don't fault unless it's
> explicitly writeprotect, which is mandatory in a few archs, x86 not).

actually get_user_pages doesn't fault either but it calls into
set_page_dirty, however get_user_pages (unlike a userland-write) at
least requires mmap_sem in read mode and the PT lock as serialization,
userland writes don't, they just go ahead and mark the pte in hardware
w/o faults. Anyway anonymous memory these days always mapped with
dirty bit set regardless, even for read-faults, after Nick finally
rightfully cleaned up the zero-page trick.
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