* pci-gart_64.c: could we get better explanation?
@ 2008-05-26 18:47 Pavel Machek
2008-05-26 19:51 ` Benjamin Herrenschmidt
0 siblings, 1 reply; 4+ messages in thread
From: Pavel Machek @ 2008-05-26 18:47 UTC (permalink / raw)
To: kernel list, Ingo Molnar, Dave Jones, Andi Kleen; +Cc: Benjamin Herrenschmidt
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
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: pci-gart_64.c: could we get better explanation?
2008-05-26 18:47 pci-gart_64.c: could we get better explanation? Pavel Machek
@ 2008-05-26 19:51 ` Benjamin Herrenschmidt
2008-06-25 22:25 ` Pavel Machek
0 siblings, 1 reply; 4+ messages in thread
From: Benjamin Herrenschmidt @ 2008-05-26 19:51 UTC (permalink / raw)
To: Pavel Machek; +Cc: kernel list, Ingo Molnar, Dave Jones, Andi Kleen
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.
Ben.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: pci-gart_64.c: could we get better explanation?
2008-05-26 19:51 ` Benjamin Herrenschmidt
@ 2008-06-25 22:25 ` Pavel Machek
2008-06-26 13:17 ` Ingo Molnar
0 siblings, 1 reply; 4+ messages in thread
From: Pavel Machek @ 2008-06-25 22:25 UTC (permalink / raw)
To: Benjamin Herrenschmidt
Cc: kernel list, Ingo Molnar, Dave Jones, Andi Kleen,
Trivial patch monkey
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.
---
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
^ permalink raw reply related [flat|nested] 4+ messages in thread
end of thread, other threads:[~2008-06-26 13:18 UTC | newest]
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2008-05-26 18:47 pci-gart_64.c: could we get better explanation? Pavel Machek
2008-05-26 19:51 ` Benjamin Herrenschmidt
2008-06-25 22:25 ` Pavel Machek
2008-06-26 13:17 ` Ingo Molnar
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