On Mon 16-07-18 21:02:02, Baoquan He wrote: > On 07/16/18 at 01:38pm, Michal Hocko wrote: > > On Fri 13-07-18 07:52:40, Baoquan He wrote: > > > Hi Michal, > > > > > > On 07/12/18 at 02:32pm, Michal Hocko wrote: > > [...] > > > > I am not able to find the beginning of the email thread right now. Could > > > > you summarize what is the actual problem please? > > > > > > The bug is found on x86 now. > > > > > > When added "kernelcore=" or "movablecore=" into kernel command line, > > > kernel memory is spread evenly among nodes. However, this is right when > > > KASLR is not enabled, then kernel will be at 16M of place in x86 arch. > > > If KASLR enabled, it could be put any place from 16M to 64T randomly. > > > > > > Consider a scenario, we have 10 nodes, and each node has 20G memory, and > > > we specify "kernelcore=50%", means each node will take 10G for > > > kernelcore, 10G for movable area. But this doesn't take kernel position > > > into consideration. E.g if kernel is put at 15G of 2nd node, namely > > > node1. Then we think on node1 there's 10G for kernelcore, 10G for > > > movable, in fact there's only 5G available for movable, just after > > > kernel. > > > > OK, I guess I see that part. But who is going to use movablecore along > > with KASLR enabled? I mean do we really have to support those two > > obscure command line parameters for KASLR? > > Not very sure whether we have to support both of those to work with > KASLR. Maybe it's time to make clear of it now. Yes, I would really like to deprecate this. It is an ugly piece of code and it's far from easily maintainable as well. > For 'kernelcore=mirror', we have solved the conflict to make it work well > with KASLR. For 'movable_node' conflict with KASLR, Chao is posting > patches to fix it. As for 'kernelcore=' and 'movablecore=', > > 1) solve the conflict between them with KASLR in > find_zone_movable_pfns_for_nodes(); > 2) disable KASLR when 'kernelcore=' | 'movablecore=' is set; > 3) disable 'kernelcore=' | 'movablecore=' when KASLR is enabled; > 4) add note in doc to notice people to not add them at the same time; I would simply warn that those kernel parameters are not supported anymore. If somebody shows up with a valid usecase we can reconsider. > 2) and 3) may need be fixed in arch/x86 code. As long as come to an > agreement, any one is fine to me. > > > > In fact I would be much more concerned about memory hotplug and > > pre-defined movable nodes. Does the current KASLR code work in that > > case? > > As said above, kernelcore=mirror works well with KASLR now. Making > 'movable_node' work with KASLR is in progress. OK, thanks for the info. -- Michal Hocko SUSE Labs
