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.
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.
Regards,
Daniel
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