From mboxrd@z Thu Jan 1 00:00:00 1970 From: eric.auger@redhat.com (Auger Eric) Date: Fri, 11 Nov 2016 17:45:19 +0100 Subject: [RFC v2 8/8] iommu/arm-smmu: implement add_reserved_regions callback In-Reply-To: <20161111162211.GU2078@8bytes.org> References: <1478258646-3117-1-git-send-email-eric.auger@redhat.com> <1478258646-3117-9-git-send-email-eric.auger@redhat.com> <20161110154606.GH2078@8bytes.org> <04ed9694-707d-260b-70c6-f367d292ceca@redhat.com> <20161110161331.GJ2078@8bytes.org> <20161111114223.GP2078@8bytes.org> <79da09b8-ac1e-cebf-5393-7d67f002b3e3@redhat.com> <20161111162211.GU2078@8bytes.org> Message-ID: <634ac375-3507-6926-164f-e67f7c798c98@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Joerg, On 11/11/2016 17:22, Joerg Roedel wrote: > Hi Eric, > > On Fri, Nov 11, 2016 at 04:47:01PM +0100, Auger Eric wrote: >> Effectively in passthrough use case, the userspace defines the address >> space layout and maps guest RAM PA=IOVA to PAs (using >> VFIO_IOMMU_MAP_DMA). But this address space does not comprise the MSI >> IOVAs. Userspace does not care about MSI IOMMU mapping. So the MSI IOVA >> region must be allocated by either the VFIO driver or the IOMMU driver I >> think. Who else could initialize the IOVA allocator domain? > > So I think we need a way to tell userspace about the reserved regions > (per iommu-group) so that userspace knows where it can not map anything, Current plan is to expose that info through an iommu-group sysfs attribute, as you and Robin advised. > and VFIO can enforce that. But the right struct here is not an > iova-allocator rb-tree, a ordered linked list should be sufficient. I plan a linked list to store the reserved regions (P2P regions, MSI region, ...). get_dma_regions is called with a list local to a function for that. Might be needed to move that list head in the iommu_group to avoid calling the get_dm_regions again in the attribute show function? But to allocate the IOVAs within the MSI reserved region, I understand you don't want us to use the iova.c allocator, is that correct? We need an allocator though, even a very basic one based on bitmap or whatever. There potentially have several different physical MSI frame pages to map. Best Regards Eric > > > Joerg >