> From: Peter Xu [mailto:pet...@redhat.com] > Sent: Friday, December 02, 2016 1:59 PM > > On Thu, Dec 01, 2016 at 04:21:38AM +0000, Tian, Kevin wrote: > > > From: Peter Xu > > > Sent: Wednesday, November 30, 2016 5:24 PM > > > > > > On Mon, Nov 28, 2016 at 05:51:50PM +0200, Aviv B.D wrote: > > > > * intel_iommu's replay op is not implemented yet (May come in different > > > > patch > > > > set). > > > > The replay function is required for hotplug vfio device and to move > > > > devices > > > > between existing domains. > > > > > > I am thinking about this replay thing recently and now I start to > > > doubt whether the whole vt-d vIOMMU framework suites this... > > > > > > Generally speaking, current work is throwing away the IOMMU "domain" > > > layer here. We maintain the mapping only per device, and we don't care > > > too much about which domain it belongs. This seems problematic. > > > > > > A simplest wrong case for this is (let's assume cache-mode is > > > enabled): if we have two assigned devices A and B, both belong to the > > > same domain 1. Meanwhile, in domain 1 assume we have one mapping which > > > is the first page (iova range 0-0xfff). Then, if guest wants to > > > invalidate the page, it'll notify VT-d vIOMMU with an invalidation > > > message. If we do this invalidation per-device, we'll need to UNMAP > > > the region twice - once for A, once for B (if we have more devices, we > > > will unmap more times), and we can never know we have done duplicated > > > work since we don't keep domain info, so we don't know they are using > > > the same address space. The first unmap will work, and then we'll > > > possibly get some errors on the rest of dma unmap failures. > > > > Tianyu and I discussed there is a bigger problem: today VFIO assumes > > only one address space per container, which is fine w/o vIOMMU (all devices > > in > > same container share same GPA->HPA translation). However it's not the case > > when vIOMMU is enabled, because guest Linux implements per-device > > IOVA space. If a VFIO container includes multiple devices, it means > > multiple address spaces required per container... > > IIUC the vfio container is created in: > > vfio_realize > vfio_get_group > vfio_connect_container > > Along the way (for vfio_get_group()), we have: > > group = vfio_get_group(groupid, pci_device_iommu_address_space(pdev), errp); > > Here the address space is per device. If without vIOMMU, they will be > pointed to the same system address space. However if with vIOMMU, > that address space will be per-device, no? >
yes, I didn't note that fact. Tianyu also pointed it out in his reply. :-) Thanks Kevin
