On Thu, May 14, 2020 at 12:36:28AM +0200, Daniel Borkmann wrote: > > So on say s390 TASK_SIZE_USUALLy is (-PAGE_SIZE), which means we'd alway > > try the user copy first, which seems odd. > > > > I'd really like to here from the bpf folks what the expected use case > > is here, and if the typical argument is kernel or user memory. > > It's used for both. Given this is enabled on pretty much all program types, my > assumption would be that usage is still more often on kernel memory than user > one.
Then it needs an argument telling it which one to use. Look at sparc64. Or s390. Or parisc. Et sodding cetera. The underlying model is that the kernel lives in a separate address space. Yes, on x86 it's actually sharing the page tables with userland, but that's not universal. The same address can be both a valid userland one _and_ a valid kernel one. You need to tell which one do you want.
