On Fri, Jun 03, 2016 at 05:10:48PM +1000, David Gibson wrote: > On Fri, Jun 03, 2016 at 11:19:44AM +0530, Bharata B Rao wrote: > > Memory hotplug can fail for some combinations of RAM and maxmem when > > DDW is enabled in the presence of devices like nec-usb-xhci. DDW depends > > on maximum addressable memory returned by guest and this value is currently > > being calculated wrongly by the guest kernel routine memory_hotplug_max(). > > While there is an attempt to fix the guest kernel, this patch works > > around the problem within QEMU itself. > > > > memory_hotplug_max() routine in the guest kernel arrives at max > > addressable memory by multiplying lmb-size with the lmb-count obtained > > from ibm,dynamic-memory property. There are two assumptions here: > > > > - All LMBs are part of ibm,dynamic memory: This is not true for PowerKVM > > where only hot-pluggable LMBs are present in this property. > > - The memory area comprising of RAM and hotplug region is contiguous: This > > needn't be true always for PowerKVM as there can be gap between > > boot time RAM and hotplug region. > > > > This work around involves having all the LMBs (RMA, rest of the boot time > > LMBs and hot-pluggable LMBs) as part of ibm,dynamic-memory so that > > guest kernel's calculation of max addressable memory comes out correct > > resulting in correct DDW value which prevents memory hotplug failures. > > memory@0 is created for RMA, but RMA LMBs are also represented as > > "reserved" LMBs in ibm,dynamic-memory. Parts of this are essenitally a > > revert of e8f986fc57a664a74b9f685b466506366a15201b. > > > > In addition to this, the alignment of hotplug memory region is reduced from > > current 1G to 256M (LMB size in PowerKVM) so that we don't end up with any > > gaps between boot time RAM and hotplug region. > > Hmm.. could we work around the problem without altering the memory > alignment by inserting extra dummy reserved LMBs covering the gap?
Appears possible, let me see if it can be done by w/o creating the DRC objects for such reserved LMBs. Regards, Bharata.
