On 10/11/2011 12:23 AM, tj@xxxxxxxxxx wrote: > Hello, > > On Mon, Oct 10, 2011 at 08:34:43PM +0200, Borislav Petkov wrote: >> On Mon, Oct 10, 2011 at 02:08:48PM -0400, tj@xxxxxxxxxx wrote: >>> Maybe I'm confused but is that patch correct for actual CPU hotplug >>> case? If not, what's the point in doing that? What are we gonna do >>> after six month some people come up with "CPU hotplug fails to load >>> new microcode for the new CPU"? >> >> Ok, first of all, we still will load ucode on the onlining path - we're >> simply not going to reload it when the CPU has gone offline and onlined >> again. For that case people should simply reload the module so that >> ucode on _all_ CPUs is updated pretty much at same time. > > I was thinking about hot-swap. It might be pretty unlikely at this > point but I don't think excluding that is a good idea. x86 is used in > pretty highend too these days. Again, I don't know much about how > ucodes are supposed to be managed and maybe it's true that we don't > need new one at all even after hotswap. If that's the case, state it > clearly and it's all fine. > >>> The invalidation code is there for a reason. >> >> ... and that reason being? > > Again, the CPU for the microcode is going away? It's something tied > to a device and the device is going away. It's a basic correctness > issue. It at least needs to be revalidated. > >>> If somebody is sure that microcode don't need to be changed once >>> loaded, then all's good and dandy but that's not the case here, right? >> >> Well, basically the current situation didn't change the ucode - it >> simply reloaded the same image from before going offline. >> >> See, there's this another problem with what we have right now: imagine >> you've just updated the ucode image on disk and offline only a subset of >> the cores. Then you online them again and they now get the newer ucode >> image while the others still run the old ucode. This could explode or >> could not, one thing's for sure: all bets are off. If we don't reload it >> on hotplug, we're fine - only module reload triggers the ucode update in >> a fairly synchronized manner. > > Yeah, loading different ucodes to different cores sounds pretty scary. > I suppose we'll need to distinguish physical hotplugs from logical > ones. > > Hmm... is it possible to tell whether the core coming online is the > same one as the last time? If that's possible, the problem becomes > pretty simple and we can simply tell people who are mixing > suspend/hibernate with physical hotplug that they're crazy. > I think that is pretty easy, atleast from a microcode revision standpoint: the collect_cpu_info() function (defined in arch/x86/kernel/microcode_core.c and arch/x86/kernel/microcode_intel.c or ..._amd.c) can be used for that purpose. Am I right Boris? -- Regards, Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> Linux Technology Center, IBM India Systems and Technology Lab -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
