linux-kernel - Re: Attansic L1 page corruption (was: 2.6.22-rc5: pdflush oops under heavy disk load)

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Date:	Mon, 25 Jun 2007 14:58:14 +0200
From:	Luca <kronos.it@...il.com>
To:	"Jay L. T. Cornwall" <jay@...na.co.uk>
Cc:	"Jay Cliburn" <jacliburn@...lsouth.net>,
	linux-kernel@...r.kernel.org, "Chris Snook" <csnook@...hat.com>,
	"huang xiong" <xiong.huang@...eros.com>
Subject: Re: Attansic L1 page corruption (was: 2.6.22-rc5: pdflush oops under heavy disk load)

On 6/25/07, Jay L. T. Cornwall <jay@...na.co.uk> wrote:
> Jay Cliburn wrote:
>
> > For reasons not yet clear to me, it appears the L1 driver has a bug or
> > the device itself has trouble with DMA in high memory.  This patch,
> > drafted by Luca Tettamanti, is being explored as a workaround.  I'd be
> > interested to know if it fixes your problem.
>
> Yes, it certainly seems to. Now running with this patch and 4GB active,
> I've transferred about 15GB with no problem so far. It usually oopses
> after a GB or two.
>
> I guess it's not an ideal solution, architecturally speaking, but it's a
> good deal better than an unstable driver.

It may cause a "bounce" (i.e. data is copied to another buffer in
lower memory) when a skb is allocated in high memory. Furthermore - at
least on AMD systems - it should be possible to use the IOMMU to remap
the memory to a bus address < 4GB.

Xiong can you comment on this issue? To recap: users are seeing hard
locks when L1 driver does a DMA to/from a high memory area (physical
address > 4GB). Limiting DMA to the lower 4GB with:

pci_set_dma_mask(pdev, DMA_32BIT_MASK);

cures the issue. Does L1 have any know problem decoding 64 addresses?

Luca
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