> I don't see how it could. Kernel data structures don't go on pagecache pages.
Kernel data structures could end up on a pagecache page: all it takes is a reference counting bug and the page could be reallocated in the kernel heap, which is directly mapped by user space. Keeping user-mapped pages and pagecache pages distinct makes this less likely.
I am otherwise not convinced that there is an actual problem with OpenBSD's coherency plan.
Kernel data structures could end up on a pagecache page: all it takes is a reference counting bug and the page could be reallocated in the kernel heap, which is directly mapped by user space. Keeping user-mapped pages and pagecache pages distinct makes this less likely.
I am otherwise not convinced that there is an actual problem with OpenBSD's coherency plan.