From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Does xc_map_foreign_pages() update IOMMU tables? Date: Thu, 13 May 2010 13:00:04 +0100 Message-ID: References: <4BEBE70B.3080706@invisiblethingslab.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4BEBE70B.3080706@invisiblethingslab.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Joanna Rutkowska , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 13/05/2010 12:48, "Joanna Rutkowska" wrote: > Does the xc_map_foreign_pages() update also the IOMMU/VT-d tables so > that the mapped pages belong also to Dom0 (from the IOMMU point of view)? Seeing as how xc_map_foreign_pages() maps pages into a particular guest-process virtual address space, whereas IOMMU tables are a mapping from guest-physical address space, it's clear that x_m_f_p() cannot sensibly be having any effect on the IOMMU. -- Keir > It seems like it does indeed. We use this function in Qubes GUI > virtualization to map composition buffers from DomUs into Dom0. Then we > use XShmPutImage() in Dom0 to display them. We've been told [1] that > XShmPutImage() often uses DMA to copy pages to the video memory, > especially in case of accelerated drivers. And we verified that our GUI > works fine on VT-d systems e.g. with Intel drivers with h/w acceleration > enabled and with iommu=pv enabled. This suggests that > xc_map_foreign_pages() indeed must be adding mapped pages to the IOMMU > tables for Dom0, as otherwise XShmPutImage() would not be able to > DMA-read the contents of those pages, that originally belonged to some > other DomUs. > > Am I missing something? If not, can somebody point me to the actual code > in Xen which does this update? > > Thanks a lot! > joanna. > > [1] http://groups.google.com/group/qubes-devel/msg/9d23cd9c26127ed7 >