On Fri, Apr 05, 2019 at 05:07:18PM +0200, Thomas Gleixner wrote: > The current implementation of in_exception_stack() iterates over the > exception stacks array. Most of the time this is an useless exercise, but > even for the actual use cases (perf and ftrace) it takes at least 2 > iterations to get to the NMI stack. > > As the exception stacks and the guard pages are page aligned the loop can > be avoided completely. > > Add a initial check whether the stack pointer is inside the full exception > stack area and leave early if not. > > Create a lookup table which describes the stack area. The table index is > the page offset from the beginning of the exception stacks. So for any > given stack pointer the page offset is computed and a lookup in the > description table is performed. If it is inside a guard page, return. If > not, use the descriptor to fill in the info structure. > > The table is filled at compile time and for the !KASAN case the interesting > page descriptors exactly fit into a single cache line. Just the last guard > page descriptor is in the next cacheline, but that should not be accessed > in the regular case. > > Signed-off-by: Thomas Gleixner <t...@linutronix.de> > --- > V2: Simplify the macro maze
This is indeed a little better. It's friday, have an ack. Acked-by: Josh Poimboeuf <jpoim...@redhat.com> I don't like the clever ISTACK_* macro naming however... -- Josh
