> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Saturday, April 23, 2022 12:59 AM > > On Fri, Apr 22, 2022 at 12:32:58AM +0000, Tian, Kevin wrote: > > > From: Tian, Kevin > > > Sent: Friday, April 22, 2022 8:13 AM > > > > > > > From: Christoph Hellwig <hch@xxxxxx> > > > > Sent: Thursday, April 21, 2022 1:41 PM > > > > > > > > I can see why a specific error might be nice for some cases and am > > > > open to that, but as a simple transformation this already looks good: > > > > > > > > > > There is a slight semantics change together with patch7. > > > > > > Before patch7 the container must be attached before calling > > > KVM_DEV_VFIO_GROUP_ADD, otherwise vfio_group_get_external_user() > > > will fail. In this case the result of cache coherency for a group is > > > deterministic, either true or false. > > No, it isn't. The coherency is a propery of the iommu_domain/container > and it can change when more groups are attached to the same > domain. The best KVM can say is that if it is reporting coherency > enforced it won't stop reporting that - which doesn't change in this > series. You are right. I thought this interface returns the domain property which should be locked down once being attached by a group but it actually checks the container property which is dynamic as you pointed out.
