On Fri, Dec 21, 2018 at 01:10:13PM -0500, Michael S. Tsirkin wrote: > On Sat, Dec 22, 2018 at 01:34:01AM +0800, Yu Zhang wrote: > > On Fri, Dec 21, 2018 at 12:15:26PM -0500, Michael S. Tsirkin wrote: > > > On Sat, Dec 22, 2018 at 12:19:20AM +0800, Yu Zhang wrote: > > > > > I'd like to avoid poking at the CPU from VTD code. That's all. > > > > > > > > OK. So for the short term，how about I remove the check of host cpu, and > > > > add a TODO > > > > in the comments in vtd_decide_config()? > > > > > > My question would be what happens on an incorrect use? > > > > I believe the vfio_dma_map will return failure for an incorrect use. > > > > > And how does user figure out which values to set? > > > > Well, for now I don't think user can figure out. E.g. if we expose a vIOMMU > > with > > 48-bit IOVA capability, yet host only supports 39-bit IOVA, vfio shall > > return failure, > > but the user does not know whose fault it is. > > > > > > > As to the check against hardware IOMMU, Peter once had a proposal in > > > > http://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg02281.html > > > > > > > > Do you have any comment or suggestion on Peter's proposal? > > > > > > Sounds reasonable to me. Do we do it on vfio attach or unconditionally? > > > > > > > I guess on vfio attach? Will need more thinking in it. > > > Things like live migration (e.g. after hot removal of the vfio device) > are also concerns.
Sorry, why live migration shall be a problem? I mean, if the DMA address width of vIOMMU does not match the host IOMMU's, we can just stop creating the VM, there's no live migration. > > > > > > > > I still do not quite know > > > > how to do it for now... > > > > > > > > [...] > > > > > > > > > > > > B.R. > > > > Yu > > > > > > > > > > > > -- > > > MST > > > > B.R. > > Yu B.R. Yu
