On Thu, Sep 05, 2019 at 01:09:55PM +0200, Petr Mladek wrote: > > I don't have a number, but it's very common to patch a function which > > uses jump labels or alternatives. > > Really? My impression is that both alternatives and jump_labels > are used in hot paths. I would expect them mostly in core code > that is always loaded. > > Alternatives are often used in assembly that we are not able > to livepatch anyway. > > Or are they spread widely via some macros or inlined functions? Jump labels are used everywhere. Looking at vmlinux.o in my kernel: Relocation section [19621] '.rela__jump_table' for section [19620] '__jump_table' at offset 0x197873c8 contains 11913 entries: Each jump label entry has 3 entries, so 11913/3 = 3971 jump labels. $ readelf -s vmlinux.o |grep FUNC |wc -l 46902 3971/46902 = ~8.5% ~8.5% of functions use jump labels. > > > + How often new problematic features appear? > > > > I'm not exactly sure what you mean, but it seems that anytime we add a > > new feature, we have to try to wrap our heads around how it interacts > > with the weirdness of late module patching. > > I agree that we need to think about it and it makes complications. > Anyway, I think that these are never the biggest problems. > > I would be more concerned about arch-specific features that might need > special handling in the livepatch code. Everyone talks only about > alternatives and jump_labels that were added long time ago. Jump labels have been around for many years, but we somehow missed implementing klp.arch for them. As I said this resulted in panics. There may be other similar cases lurking, both in x86 and other arches. It's not a comforting thought! And each case requires special klp code in addition to the real code. -- Josh
