Hi Tixy, On Thu, Oct 17, 2013 at 04:24:01PM +0100, Jon Medhurst (Tixy) wrote: > On Thu, 2013-10-17 at 12:38 +0100, Will Deacon wrote: > > On Thu, Oct 17, 2013 at 07:19:35AM +0100, Jiang Liu wrote: > > > + /* > > > + * Execute __aarch64_insn_patch_text() on every online CPU, > > > + * which ensure serialization among all online CPUs. > > > + */ > > > + return stop_machine(aarch64_insn_patch_text_cb, &patch, NULL); > > > +} > > > > Whoa, whoa, whoa! The comment here is wrong -- we only run the patching on > > *one* CPU, which is the right thing to do. However, the arch/arm/ call to > > stop_machine in kprobes does actually run the patching code on *all* the > > online cores (including the cache flushing!). I think this is to work around > > cores without hardware cache maintenance broadcasting, but that could easily > > be called out specially (like we do in patch.c) and the flushing could be > > separated from the patching too. > [...] > > For code modifications done in 32bit ARM kprobes (and ftrace) I'm not > sure we ever actually resolved the possible cache flushing issues. If > there was specific reasons for flushing on all cores I can't remember > them, sorry. I have a suspicion that doing so was a case of sticking > with what the code was already doing, and flushing on all cores seemed > safest to guard against problems we hadn't thought about.
[...] > Sorry, I don't think I've added much light on things here have I? I think you missed the bit I was confused about :) Flushing the cache on each core is necessary if cache_ops_need_broadcast, so I can understand why you'd have code to do that. The bit I don't understand is that you actually patch the instruction on each core too! Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
