On 19/12/2018 23:09, Michael S. Tsirkin wrote: > On Thu, Dec 13, 2018 at 12:50:29PM +0000, Jean-Philippe Brucker wrote: >>>> [3] git://linux-arm.org/linux-jpb.git virtio-iommu/v0.9.1 >>>> git://linux-arm.org/kvmtool-jpb.git virtio-iommu/v0.9 >>> >>> Unfortunatly gitweb seems to be broken on linux-arm.org. What is missing >>> in this patch-set to make this work on x86? >> >> You should be able to access it here: >> http://www.linux-arm.org/git?p=linux-jpb.git;a=shortlog;h=refs/heads/virtio-iommu/devel >> >> That branch contains missing bits for x86 support: >> >> * ACPI support. We have the code but it's waiting for an IORT spec >> update, to reserve the IORT node ID. I expect it to take a while, given >> that I'm alone requesting a change for something that's not upstream or >> in hardware. > > Frankly I think you should take a hard look at just getting the data > needed from the PCI device itself. You don't need to depend on virtio, > it can be a small driver that gets you that data from the device config > space and then just goes away. > > If you want help with writing such a small driver let me know. > > If there's an advantage to virtio-iommu then that would be its > portability, and it all goes out of the window because > of dependencies on ACPI and DT and OF and the rest of the zoo. But the portable solutions are ACPI and DT. Describing the DMA dependency through a device would require the guest to probe the device before all others. How do we communicate this? * pass a kernel parameter saying something like "probe_first=00:01.0" * make sure that the PCI root complex is probed before any other platform device (since the IOMMU can manage DMA of platform devices). * change DT, ACPI and PCI core code to handle this probe_first kernel parameter. Better go with something standard, that any OS and hypervisor knows how to use, and that other IOMMU devices already use. >> * DMA ops for x86 (see "HACK" commit). I'd like to use dma-iommu but I'm >> not sure how to implement the glue that sets dma_ops properly. >> >> Thanks, >> Jean > > OK so IIUC you are looking into Christoph's suggestions to fix that up? Eventually yes. I'll give it a try next year, once the dma-iommu changes are on the list. It's not a priority for me, given that x86 already has a pvIOMMU with VT-d, and that Arm still needs one. It shouldn't block this series. > There's still a bit of time left before the merge window, > maybe you can make above changes. I'll wait to see if Joerg has other concerns about the design or the code, and resend in January. I think that IOMMU driver changes should go through his tree. Thanks, Jean
