From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: iommu=dom0-passthrough behavior Date: Mon, 05 Nov 2012 14:30:25 +0000 Message-ID: <5097DB9102000078000A65C7@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: wei.huang2@amd.com, weiwang.dd@gmail.com, xiantao.zhang@intel.com Cc: xen-devel List-Id: xen-devel@lists.xenproject.org All, so far it was my understanding that this option is intended to get the DMA behavior that Dom0 observes as close as possible to how it would be without IOMMU. However, we're now dealing with a customer report where a single function device is observed to initiate DMA operations appearing to originate from function 1, which makes obvious that the option above is not making things as transparent as I would have expected them to be: Without IOMMU, such requests get processed fine, while with IOMMU (due to there not being a context entry for the bogus device) the device fails to initialize (causing DMA faults, the presence of which I had to convince myself of separately, as for whatever reason at least the VT-d code doesn't issue any log message in that case). So I'm now seeking for alternative workaround suggestions that we could pass to that customer (less intrusive than "iommu=off"). Thanks, Jan