Two questions about NVDIMM devices

[Milan Zamazal]

Hi,

I've met two situations with NVDIMM support in libvirt where I'm not
sure all the parties (libvirt & I) do the things correctly.

The first problem is with memory alignment and size changes.  In
addition to the size changes applied to NVDIMMs by QEMU, libvirt also
makes some NVDIMM size changes for better alignments, in
qemuDomainMemoryDeviceAlignSize.  This can lead to the size being
rounded up, exceeding the size of the backing device and QEMU failing to
start the VM for that reason (I've experienced that actually).  I work
with emulated NVDIMM devices, not a bare metal hardware, so one might
argue that in practice the device sizes should already be aligned, but
I'm not sure it must be always the case considering labels or whatever
else the user decides to set up.  And I still don't feel very
comfortable that I have to count with two internal size adjustments
(libvirt & QEMU) to the `size' value I specify, with the ultimate goal
of getting the VM started and having the NVDIMM aligned properly to make
(non-NVDIMM) memory hot plug working.  Is the size alignment performed
by libvirt, especially rounding up, completely correct for NVDIMMs?

The second problem is that a VM fails to start with a backing NVDIMM in
devdax mode due to SELinux preventing access to the /dev/dax* device (it
doesn't happen with any other NVDIMM modes).  Who should be responsible
for handling the SELinux label appropriately in that case?  libvirt, the
system administrator, anybody else?  Using <seclabel> in NVDIMM's source
doesn't seem to be accepted by the domain XML schema.

Thanks,
Milan