> From: Tian, Kevin <kevin.tian@xxxxxxxxx> > Sent: Tuesday, March 7, 2023 10:31 AM > > > From: Jason Gunthorpe <jgg@xxxxxxxxxx> > > Sent: Monday, March 6, 2023 9:17 PM > > > > On Fri, Mar 03, 2023 at 09:55:42AM -0700, Alex Williamson wrote: > > > > > I can't think of a reason DPDK couldn't use hot-reset. If we want to > > > make it a policy, it should be enforced by code, but creating that > > > policy based on a difficulty in supporting that mode with iommufd isn't > > > great. > > > > On the other hand adding code to allow device FDs in the hot reset > > path that is never used and never tested isn't great either.. > > > > hot-reset does work for DPDK, it just doesn't work in the case where > > DPDK would have many VFIO devices open and they have overlapping > > device sets. Which, again, is something it doesn't do. > > > > IMHO we should leave it out of the kernel and wait for a no-iommu user > > to come forward that wants hot-reset of many devices. Then we can add > > and test the device FD part. Most likely such a thing will never come > > at this point. > > > > I think we don't need to have this tradeoff if following Yi's last proposal > which requires every opened device in the set to be covered by the > device fd array. with dev_set->lock held in the reset/open path this is > a safe measure and fully contained in vfio-pci w/o need of further > checking noiommu or iommufd. > > In the end same reset uAPI except the fd array can be device fd now. 😊 > > btw Yi, since this also affects the group path (though positive) it's clearer > to first add open_count check in existing group path in a separate patch > and then add the device fd support. Yes. I've made them in the below branch. I plan to send v6 out with the iommufd_access created in bind (not in the below branch yet). https://github.com/yiliu1765/iommufd/tree/vfio_device_cdev_v6 vfio/pci: Accept device fd for VFIO_DEVICE_PCI_HOT_RESET (https://github.com/yiliu1765/iommufd/commit/dcefb8ca5d13388ab9b9862992fd77cffcbadc30) vfio/pci: Only need to check opened devices in the dev_set for hot reset (https://github.com/yiliu1765/iommufd/commit/f7257f2db958d9d961a6e45ab0e301ee0397a243) Regards, Yi Liu
