On 2018-10-04 21:33, H. Peter Anvin wrote: > Here is the horrible code I mentioned yesterday. This is about > implementing the immediate-patching framework that Linus and others have > discussed (it helps both performance and kernel hardening):
Heh, I did a POC in userspace some years ago for loading an "eventually constant" value into a register - the idea being to avoid a load in cases like kmemcache_alloc(foo_cachep) or kmemcache_free(foo_cachep, p), and I assume this is something along the same lines? I didn't do anything with it since I had no idea if the performance gain would be worth it, and at the time (before __ro_after_init) there was no good way to know that the values would really be constant eventually. Also, I had hoped to come up with a way to avoid having to annotate the loads. I just tried expanding this to deal with some of the hash tables sized at init time which I can see was also mentioned on LKML some time ago. I'm probably missing something fundamental, but there's some sorta working code at https://github.com/villemoes/rai which is not too horrible (IMO). Attaching gcc at various times and doing disassembly shows that the patching does take place. Can I get you to take a look at raimacros.S and tell me why that won't work? Thanks, Rasmus
