linux-kernel - Re: [Intel-gfx] [PATCH 2/2] drm/i915: properly prefault for pread/pwrite

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Date:	Thu, 03 Nov 2011 14:06:55 -0700
From:	Keith Packard <keithp@...thp.com>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	Daniel Vetter <daniel@...ll.ch>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>, stable@...nel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Morton\, Andrew" <akpm@...ux-foundation.org>
Subject: Re: [Intel-gfx] [PATCH 2/2] drm/i915: properly prefault for pread/pwrite

On Mon, 24 Oct 2011 00:11:57 +0200, Daniel Vetter <daniel@...ll.ch> wrote:

> This patch only fixes things up so that we prefault the entire page range
> and not just the first PAGE_SIZE bytes (i.e. at most 2 pages). So I don't
> see the risk of extending the current behaviour to all pages. Userspace
> can already see these zero writes, but only when doing something stupid.

When we posted a patch to instead fix fault_in_pages_writeable, Andrew
complained that we'd have modified memory even on a short read, which
wasn't considered polite. Could we read/write the same value and avoid
that problem?

Also, we should be fixing fault_in_pages_* going forward, rather than
kludging in more code. And, we'd get to remove the version in ntfs,
which should end in a patch that removes more code than it adds...

-- 
keith.packard@...el.com

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