Daniel P. Berrangé <berrange@xxxxxxxxxx> writes: > On Tue, Jun 16, 2020 at 12:54:29PM +0200, Milan Zamazal wrote: >> Hi, >> > >> I've found out that NVDIMM size and label size matter for regular >> (non-NV) DIMM hot plug. If the NVDIMM is not aligned correctly, the >> guest OS will not accept the hot plugged memory and will complain with >> messages such as >> >> Block size [0x8000000] unaligned hotplug range: start 0x225000000, size 0x10000000 >> >> The start address above is also reported within <memory> element of the >> hot plugged memory in the domain XML: >> >> <address type='dimm' slot='1' base='0x225000000'/> >> >> Apparently, in order to make memory hot plug working in the guest OS, >> the inserted memory must be aligned to the platform memory alignment >> (128 MB on x86_64). >> >> I'd like to clarify, how libvirt makes the DIMM address above. How is >> the NVDIMM memory range determined? According to my experiments, it >> seems the NVDIMM specified <size> is taken, NVDIMM <label> size is >> subtracted from it and the resulting value is reduced to the nearest >> multiple of NVDIMM <alignsize>. Is this observation correct? Is it >> guaranteed to be stable in future versions? I need to determine the >> right NVDIMM size to make the subsequent memory modules correctly >> aligned and then I can't change the NVDIMM size, to not damage data >> stored in the NVDIMM. > > Libvirt doesn't ever assign a "base" address value itself. We just > start QEMU, and then fill in the XML "base" with the value that QEMU > has assigned. I see, then I'll ask about it on the QEMU list. >> Additionally, when adjusting maxMemory due to NVDIMM presence, should I >> increase it by the specified NVDIMM <size> or a different value? > > IIRC, maxMemory has to allow for the sum of the basic RAM amount, plus > RAM intended to be used for all possible future (NV)DIMMS that will be > hotplugged. OK. Thanks, Milan
