On 23.04.2018 17:32, Pankaj Gupta wrote: > > Hi Igor, > >> >>> Right now we can only map PCDIMM/NVDIMM into guest address space. In the >>> future, we might want to do the same for virtio devices - e.g. >>> virtio-pmem or virtio-mem. Especially, they should be able to live side >>> by side to each other. >>> >>> E.g. the virto based memory devices regions will not be exposed via ACPI >>> and friends. They will be detected just like other virtio devices and >>> indicate the applicable memory region. This makes it possible to also use >>> them on architectures without memory device detection support (e.g. s390x). >>> >>> Let's factor out the memory device code into a MemoryDevice interface. >> A couple of high level questions as relevant code is not here: >> >> 1. what would hotplug/unplug call chain look like in case of virtio-pmem >> device >> (reason I'm asking is that pmem being PCI device would trigger >> PCI bus hotplug controller and then it somehow should piggyback >> to Machine provided hotplug handlers, so I wonder what kind of >> havoc it would cause on hotplug infrastructure) > > For first phase we are using 'virtio-pmem' as cold added devices. AFAIU > 'VirtioDeviceClass' being parent class and 'hotplug/unplug' methods > implemented > for virtio-pmem device. So, pci bus hotplug/unplug should call the > corresponding > functions? > >> >> 2. why not use PCI bar mapping mechanism to do mapping since pmem is PCI >> device? > > I think even we use if as PCI BAR mapping with PCI we still need free guest > physical > address to provide to VM for mapping the memory range. For that there needs > to > be coordination between PCDIMM and VIRTIO pci device? Also, if we use RAM > from QEMU > address space tied to big region(system_memory) memory accounting gets easier > and at single place. > > Honestly speaking I don't think there will be much difference between the two > approaches? unless > I am missing something important?
The difference by gluing virtio devices to architecture specific technologies will be unnecessary complicated. (my humble opinion) -- Thanks, David / dhildenb
