Messages in this thread Patch in this message | | | Date | Thu, 26 Jun 2008 00:25:43 +0200 | From | Pavel Machek <> | Subject | Re: pci-gart_64.c: could we get better explanation? |
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On Tue 2008-05-27 05:51:39, Benjamin Herrenschmidt wrote: > > On Mon, 2008-05-26 at 20:47 +0200, Pavel Machek wrote: > > 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? > > P2P bridge prefetching on DMA reads.
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Add better explanation to pci-gart.
Signed-off-by: Pavel Machek <pavel@suse.cz>
diff --git a/arch/x86/kernel/pci-gart_64.c b/arch/x86/kernel/pci-gart_64.c index 838a1d3..e72e583 100644 --- a/arch/x86/kernel/pci-gart_64.c +++ b/arch/x86/kernel/pci-gart_64.c @@ -800,10 +800,10 @@ #endif wbinvd(); /* - * Try to workaround a bug (thanks to BenH) + * 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 - * then. + * then. (P2P bridge may be prefetching on DMA reads). */ scratch = get_zeroed_page(GFP_KERNEL); if (!scratch) -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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