[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] question on iommu _map_page
On May 28, 2010, at 3:08 AM, Keir Fraser wrote: > On 27/05/2010 21:59, "Kaushik Kumar Ram" <kaushik@xxxxxxxx> wrote: > >> On May 27, 2010, at 3:46 PM, Keir Fraser wrote: >> >>> It looks like the person who implemented that never needed the read-only >>> case. We need a function to map pages into the iommu read-only and to call >>> that from the grant code. >>> >>> A patch to just call iommu_map_page() for any kind of grant mapping would be >>> acceptable for now, if you want to submit a patch. >> >> OK. Attached. > > Actually I've implemented the better fix as xen-unstable:21476. Hope that > works okay for you. Checking if act->pin is zero before calling iommu_unmap_page() (in grant_table.c) is not sufficient since there can be multiple active grants all referring to the same mfn. In fact I came across iommu page faults because pages were getting unmapped from the IOMMU when active grants referring to these pages were still around. Ideally, there needs to be a per-page count of how many IOMMU mappings exists for a page. I can't think of an obvious fix for this problem. For my purposes, I hacked page_info to add another counter which I guess is not an acceptable solution! -Kaushik _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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