On Fri, Dec 2, 2016 at 11:03 AM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Fri, Dec 2, 2016 at 10:50 AM, Borislav Petkov <b...@kernel.org> wrote: >> >> Right, we can try to do something like invalidate_icache() or so in >> there with the JMP so that the BSP refetches modified code and see where >> it gets us. > > I'd really rather rjust mark it noinline with a comment. That way the > return from the function acts as the control flow change. > >> The good thing is, the early patching paths run before SMP is >> up but from looking at load_module(), for example, which does >> post_relocation()->module_finalize()->apply_alternatives(), this can >> happen late. >> >> Now there I'd like to avoid other cores walking into that address being >> patched. Or are we "safe" there in the sense that load_module() happens >> on one CPU only sequentially? (I haven't looked at that code to see >> what's going on there, actually). > > 'sync_core()' doesn't help for other CPU's anyway, you need to do the > cross-call IPI. So worrying about other CPU's is *not* a valid reason > to keep a "sync_core()" call. > > Seriously, the only reason I can see for "sync_core()" really is: > > - some deep non-serialized MSR access or similar (ie things like > firmware loading etc really might want it, and a mchine check might > want it)
Not even firmware loading wants it. Firmware loading needs specifically cpuid(eax=1). It has nothing to do with serializing anything -- it's just a CPU bug that was turned into "architecture". I think it really is just cross-address or cross-core modification, and I'll add a comment to that effect. --Andy
