On Thu, 5 May 2016 13:23:11 -0700 Neo Jia <cjia@xxxxxxxxxx> wrote: > > > I also noticed in another thread: > > > --------------------------------- > > > [Qemu-devel] [RFC PATCH v3 3/3] VFIO Type1 IOMMU change: to support with iommu and without iommu > > > > > > Kirti did: > > > 1. don't pin the pages in the map ioctl for the vGPU case. > > > 2. export vfio_pin_pages and vfio_unpin_pages. > > > > > > Although their patches didn't show how these interfaces were used, I > > > guess them can either use these interfaces to pin/unpin all of the > > > guest memory, or pin/unpin memory on demand. So can I reuse their work > > > to finish my #1? If the answer is yes, then I could change my plan and > > > > Yes, we would absolutely only want one vfio iommu backend doing this, > > there's nothing device specific about it. We're looking at supporting > > both modes of operation, fully pinned and pin-on-demand. NVIDIA vGPU > > wants the on-demand approach while Intel vGPU wants to pin the entire > > guest, at least for an initial solution. This iommu backend would need > > to support both as determined by the mediated device backend. > > Right, we will add a new callback to mediated device backend interface for this > purpose in v4 version patch. Dear Neo: Thanks for this information. What I interest most is the new vfio iommu backend. Looking forward to your new patches. :> > > Thanks, > Neo > > > > > > do: > > > #1. Introduce a vfio_iommu_type1_ccw as the vfio iommu backend for ccw. > > > When starting the guest, form the <vaddr, iova, size> database. > > > > > > #2. In the driver of the ccw devices, when an I/O instruction was > > > intercepted, call vfio_pin_pages (Kirti's version) to get the host > > > physical address, then translate the ccw program for I/O operation. > > > > > > So which one is the right way to go? > > > > As above, I think we have a need to support both approaches in this new > > iommu backend, it will be up to you to determine which is appropriate > > for your devices and guest drivers. A fully pinned guest has a latency > > advantage, but obviously there are numerous disadvantages for the > > pinning itself. Pinning on-demand has overhead to setup each DMA > > operations by the device but has a much smaller pinning footprint. -------- Dong Jia -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
