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 13:27:36 +0100 Message-ID: References: <4BEBEC09.1010503@invisiblethingslab.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4BEBEC09.1010503@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 Cc: "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 13/05/2010 13:09, "Joanna Rutkowska" wrote: >> 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. >> > Interesting. That suggests the graphics drivers we tested do not use DMA > for XShmPutImage()... Ah, actually dom0 is special in that it gets a 1:1 mapping of all of RAM (except for some private Xen areas). See drivers/passthrough/vtd/x86/vtd.c:iommu_set_dom0_mapping(). I forgot about that when I wrote my previous reply! > Anyway, what would be the recommend way of updating IOMMU mappings in > this case? Would you consider patching of x_m_f_p() an acceptable > solution? (perhaps with some additional flag: "update_iommu")? Like I said, the concept does not make sense: IOMMU tables and host page tables map from different address spaces. But of course this does not matter anyway given dom0 gets a pretty comprehensive mapping set up by default. So I think you are good to go. -- Keir