On Fri, Oct 20, 2023 at 02:43:58AM +0000, Tian, Kevin wrote: > What we want to prevent is attaching a non-CC device to a CC domain > or upgrade a non-CC domain to CC since in both case the non-CC > device will be broken due to incompatible page table format. [..] > Who cares about such consistency? sure the result is different due to order: > > 1) creating hwpt for dev1 (non-CC) then later attaching hwpt to > dev2 (CC) will succeed; > > 2) creating hwpt for dev2 (CC) then later attaching hwpt to > dev1 (non-CC) will fail then the user should create a new hwpt > for dev1; AH... So really what the Intel driver wants is not upgrade to CC but *downgrade* from CC. non-CC is the type that is universally applicable, so if we come across a non-CC capable device the proper/optimal thing is to degrade the HWPT and re-use it, not allocate a new HWPT. So the whole thing is upside down. As changing the IOPTEs in flight seems hard, and I don't want to see the Intel driver get slowed down to accomodate this, I think you are right to say this should be a creation time property only. I still think userspace should be able to select it so it can minimize the number of HWPTs required. > But the user shouldn't assume such explicit consistency since it's not > defined in our uAPI. All we defined is that the attaching may > fail due to incompatibility for whatever reason then the user can > always try creating a new hwpt for the to-be-attached device. From > this regard I don't see providing consistency of result is > necessary. 😊 Anyhow, OK, lets add a comment summarizing your points and remove the cc upgrade at attach time (sorry Nicolin/Yi!) It is easy to add a HWPT flag for this later if someone wants to optimize it. Jason
