NVDIMM was introduced to qemu in v2.6.0-rc0~248^2~25. So it's
been a while since then.

It's not the next big thing, but it is very interesting feature
enabling higher performance as reading/writing to the module (and
subsequently to the file on the host) does not require a VMEXIT.
It can be used to access host files directly bypassing page cache
whilst doing so.


How to test the feature?
1) you need PMEM enabled kernel:
  CONFIG_LIBNVDIMM=y
  CONFIG_BLK_DEV_PMEM=m
  CONFIG_ACPI_NFIT=m

2) Create a file in the host:
  truncate -s 512M /tmp/nvdimm

3) Add the following to the domain XML:

    <memory model='nvdimm' memAccess='shared'>
      <source>
        <path>/tmp/nvdimm</path>
      </source>
      <target>
        <size unit='KiB'>523264</size>
        <node>0</node>
      </target>
    </memory>

4) Start the domain and write something into the NVDIMM module:
  (guest) $ echo 'Hello world' > /dev/pmem0

5) From the host, check the file has changed:
  (host) $ hexdump -C /tmp/nvdimm


Want to watch very interesting video while reviewing?

https://youtu.be/Vit3-PjbN9M

Michal Privoznik (5):
  Introduce NVDIMM memory model
  qemu: Introduce QEMU_CAPS_DEVICE_NVDIMM
  qemu: Implement NVDIMM
  conf: Introduce memAccess to <memory/>
  qemu: Implement memAccess for <memory/> banks

 docs/formatdomain.html.in                          |  41 ++++++--
 docs/schemas/domaincommon.rng                      |  51 ++++++----
 src/conf/domain_conf.c                             | 112 ++++++++++++++++-----
 src/conf/domain_conf.h                             |   4 +
 src/libvirt_private.syms                           |   2 +
 src/qemu/qemu_alias.c                              |  12 ++-
 src/qemu/qemu_capabilities.c                       |   2 +
 src/qemu/qemu_capabilities.h                       |   1 +
 src/qemu/qemu_command.c                            |  87 +++++++++++-----
 src/qemu/qemu_command.h                            |   2 +
 src/qemu/qemu_domain.c                             |  29 ++++--
 src/qemu/qemu_hotplug.c                            |   3 +-
 tests/qemucapabilitiesdata/caps_2.6.0.x86_64.xml   |   1 +
 .../qemuxml2argv-hugepages-numa.args               |   5 +-
 .../qemuxml2argv-hugepages-pages.args              |  24 ++---
 .../qemuxml2argv-hugepages-pages2.args             |   8 +-
 .../qemuxml2argv-hugepages-pages3.args             |   4 +-
 .../qemuxml2argv-hugepages-shared.args             |  22 ++--
 .../qemuxml2argv-memory-hotplug-dimm-addr.args     |   5 +-
 .../qemuxml2argv-memory-hotplug-dimm.args          |   5 +-
 ...muxml2argv-memory-hotplug-nvdimm-memAccess.args |  26 +++++
 ...emuxml2argv-memory-hotplug-nvdimm-memAccess.xml |  49 +++++++++
 .../qemuxml2argv-memory-hotplug-nvdimm.args        |  25 +++++
 .../qemuxml2argv-memory-hotplug-nvdimm.xml         |  49 +++++++++
 tests/qemuxml2argvtest.c                           |   6 +-
 25 files changed, 452 insertions(+), 123 deletions(-)
 create mode 100644 
tests/qemuxml2argvdata/qemuxml2argv-memory-hotplug-nvdimm-memAccess.args
 create mode 100644 
tests/qemuxml2argvdata/qemuxml2argv-memory-hotplug-nvdimm-memAccess.xml
 create mode 100644 
tests/qemuxml2argvdata/qemuxml2argv-memory-hotplug-nvdimm.args
 create mode 100644 
tests/qemuxml2argvdata/qemuxml2argv-memory-hotplug-nvdimm.xml

-- 
2.8.4

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