On Thu, Nov 2, 2017 at 1:50 AM, Xiao Guangrong
<address@hidden> wrote:
[..]
Yes, the GUID will specifically identify this range as "Virtio Shared
Memory" (or whatever name survives after a bikeshed debate). The
libnvdimm core then needs to grow a new region type that mostly
behaves the same as a "pmem" region, but drivers/nvdimm/pmem.c grows a
new flush interface to perform the host communication. Device-dax
would be disallowed from attaching to this region type, or we could
grow a new device-dax type that does not allow the raw device to be
mapped, but allows a filesystem mounted on top to manage the flush
interface.
I am afraid it is not a good idea that a single SPA is used for multiple
purposes. For the region used as "pmem" is directly mapped to the VM so
that guest can freely access it without host's assistance, however, for
the region used as "host communication" is not mapped to VM, so that
it causes VM-exit and host gets the chance to do specific operations,
e.g, flush cache. So we'd better distinctly define these two regions to
avoid the unnecessary complexity in hypervisor.
Good point, I was assuming that the mmio flush interface would be
discovered separately from the NFIT-defined memory range. Perhaps via
PCI in the guest? This piece of the proposal needs a bit more
thought...