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

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Date:	Tue, 5 Feb 2013 06:57:21 -0700
From:	Shuah Khan <shuahkhan@...il.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	Shuah Khan <shuah.khan@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>, iommu@...ts.linux-foundation.org
Subject: Re: IO_PAGE_FAULTs on unity mapped regions during amd_iommu_init() in
 Linux 3.4

On Tue, Feb 5, 2013 at 6:31 AM, Joerg Roedel <joro@...tes.org> wrote:
> 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.
>

Hi Joerg,

Thanks much. I will hang on to this test system for testing your fix.

-- Shuah
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