linux-kernel - Re: IO_PAGE_FAULTs on unity mapped regions during amd_iommu

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Date:	Tue, 5 Feb 2013 14:31:05 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Shuah Khan <shuah.khan@...com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>,
	iommu@...ts.linux-foundation.org, shuahkhan@...il.com
Subject: Re: IO_PAGE_FAULTs on unity mapped regions during amd_iommu_init()
 in Linux 3.4

Hi Shuah,

On Fri, Feb 01, 2013 at 11:31:59AM -0700, Shuah Khan wrote:
> Yes, 3.7 has the same window of opportunity for this race condition,
> however I couldn't figure out why it doesn't happen on 3.7. On 3.7 the
> window between amd_iommu_init_hardware() and amd_iommu_init_dma_ops()
> might actually be wider than the window in 3.4.

I think this is highly timing related. IOMMU initialization may have
been moved by a few milliseconds between the kernel versions which might
cause the warnings to appear or disappear. I don't think it has much
value to dive deeper into the differences between the initialization
sequences.

As somethimes with such issues there is a simple and a more complex fix
for that. I'll try to come up with a simple fix for the next merge
window and implement the clean and more complex one for the next one.

	Joerg

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