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Date: Wed, 2 Jul 2014 15:32:59 +0200 From: Joerg Roedel <joro@...tes.org> To: David Woodhouse <dwmw2@...radead.org> Cc: Bill Sumner <bill.sumner@...com>, "Hoemann, Jerry" <jerry.hoemann@...com>, indou.takao@...fujitsu.com, bhe@...hat.com, linux-pci@...r.kernel.org, kexec@...ts.infradead.org, linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org, doug.hatch@...com, ishii.hironobu@...fujitsu.com, bhelgaas@...gle.com, zhenhua@...com Subject: Re: [PATCH 0/8] iommu/vt-d: Fix crash dump failure caused by legacy DMA/IO Hi David, On Wed, Apr 30, 2014 at 11:49:33AM +0100, David Woodhouse wrote: > There could be all kinds of existing mappings in the DMA page tables, > and I'm not sure it's safe to preserve them. What prevents the crashdump > kernel from trying to use any of the physical pages which are > accessible, and which could thus be corrupted by stray DMA? > > In fact, the old kernel could even have set up 1:1 passthrough mappings > for some devices, which would then be able to DMA *anywhere*. Surely we > need to prevent that? Ideally we would prevent that, yes. But the problem is that a failed DMA transaction might put the device into an unrecoverable state. Usually any in-flight DMA transactions should only target buffers set up by the previous kernel and not corrupt any data. > After the last round of this patchset, we discussed a potential > improvement where you point every virtual bus address at the *same* > physical scratch page. That is a solution to prevent the in-flight DMA failures. But what happens when there is some in-flight DMA to a disk to write some inodes or a new superblock. Then this scratch address-space may cause filesystem corruption at worst. So with this in mind I would prefer initially taking over the page-tables from the old kernel before the device drivers re-initialize the devices. Joerg -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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