linux-kernel - pci-gart_64.c: could we get better explanation?

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Message-ID: <20080526184703.GA17369@elf.ucw.cz>
Date:	Mon, 26 May 2008 20:47:03 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	kernel list <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Dave Jones <davej@...emonkey.org.uk>,
	Andi Kleen <andi@...stfloor.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: pci-gart_64.c: could we get better explanation?

Hi!

+++ b/arch/x86/kernel/pci-gart_64.c
@@ -774,6 +778,7 @@ #endif
 
        /*
         * Try to workaround a bug (thanks to BenH)
         * Set unmapped entries to a scratch page instead of 0.
         * Any prefetches that hit unmapped entries won't get an bus abort

Could someone explain? Which bug is being worked around? CPUs
prefetching over NULL?
								Pavel
-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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