> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Monday, April 17, 2023 9:39 PM > > On Fri, Apr 14, 2023 at 09:11:30AM +0000, Tian, Kevin wrote: > > > The only corner case with this option is when a user mixes group > > and cdev usages. iirc you mentioned it's a valid usage to be supported. > > In that case the kernel doesn't have sufficient knowledge to judge > > 'resettable' as it doesn't know which groups are opened by this user. > > IMHO we don't need to support this combination. Do you mean we don't support hot-reset for this combination or we don't support user using this combination. I guess the prior one. Right? > > We can say that to use the hot reset API the user must put all their > devices into the same iommufd_ctx and cover 100% of the known use > cases for this. > > There are already other situations, like nesting, that do force users > to put everything into one iommufd_ctx. > > No reason to make things harder and more complicated. Ditto. We just fail hot-reset for the multiple iommufds case. Is it? Otherwise, we need to prevent users from using multiple iommufds. > I'm coming to the feeling that we should put no-iommu devices in > iommufd_ctx's as well. They would be an iommufd_access like > mdevs. That would clean up the complications they cause here. Ok, the lucky thing is you have merged the patch series that creates iommufd_access for emulated devices in bind. So cdev series needs to handle noiommu case by creating iommufd_access. > > I suppose we should have done that from the beginning - no-iommu is an > IOMMUFD access, it just uses a crazy /proc based way to learn the > PFNs. Making it a proper access and making a real VFIO ioctl that > calls iommufd_access_pin_pages() and returns the DMA mapped addresses > to userspace would go a long way to making no-iommu work in a logical, > usable, way. This seems to be an improvement for noiommu mode. It can be done later. For now, generating access_id and binding noiommu devices with iommufdctx is enough for supporting noiommu hot-reset. Regards, Yi Liu
