On 9/20/22 06:14, Jason Gunthorpe wrote: > For this I would rather have a function that queries the format of the > page table under the mm_struct and we have enum values like > INTEL_NORMAL and INTEL_LAM as possible values. > > The iommu driver will block incompatible page table formats, and when > it starts up it should assert something that blocks changing the > format. That doesn't sound too bad. Except, please don't call it a "page table format". The format of the page tables does not change with LAM. It's entirely how the CPU interprets addresses that changes. I guess someone could make an argument that, with LAM, there is a "hole" that can't be filled in and _that_ constitutes a format change, but that'd be a stretch. The thing that matters when LAM is on is that some CPU might be stashing addresses somewhere that only have meaning when you interpret them with LAM rules. That's really a property of the mm, not of the page tables. Oh, and please don't call things "INTEL_WHATEVER". It looks silly and confuses the heck out of people when a second CPU vendor needs to use the same code.
