From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: IO_PAGE_FAULTs on unity mapped regions during amd_iommu_init() in Linux 3.4 Date: Tue, 5 Feb 2013 14:31:05 +0100 Message-ID: <20130205133104.GC2532@8bytes.org> References: <1359657210.6061.3.camel@lorien2> <20130201130035.GE25591@8bytes.org> <1359743519.2759.38.camel@lorien2> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1359743519.2759.38.camel@lorien2> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Shuah Khan Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, LKML , stable , shuahkhan-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org List-Id: iommu@lists.linux-foundation.org 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