On Tue, Feb 19, 2019 at 10:04:09AM +0100, Peter Zijlstra wrote: > > Does that make more sense? > > It appears to me you're going about it backwards.
So how about you do a GCC plugin that verifies limits on code-gen between user_access_begin/user_access_end() ? - No CALL/RET - implies user_access_end() happens - implies no fentry hooks - No __preempt_count frobbing - No tracepoints - ... That way you put the burden on the special code, not on the rest of the kernel.