[Qemu-devel] [PATCH 00/16] implement vNVDIMM

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

====== Background ======
NVDIMM (A Non-Volatile Dual In-line Memory Module) is going to be supported
on Intel's platform. They are discovered via ACPI and configured by _DSM
method of NVDIMM device in ACPI. There has some supporting documents which
can be found at:
ACPI 6: http://www.uefi.org/sites/default/files/resources/ACPI_6.0.pdf
NVDIMM Namespace: http://pmem.io/documents/NVDIMM_Namespace_Spec.pdf
DSM Interface Example: http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf
Driver Writer's Guide: http://pmem.io/documents/NVDIMM_Driver_Writers_Guide.pdf

Currently, the NVDIMM driver has been merged into upstream Linux Kernel and
this patchset tries to enable it in virtualization field

====== Design ======
NVDIMM supports two mode accesses, one is PMEM which maps NVDIMM into CPU's
address space then CPU can directly access it as normal memory, another is
BLK which is used as block device to reduce the occupying of CPU address
space

BLK mode accesses NVDIMM via Command Register window and Data Register window.
BLK virtualization has high workload since each sector access will cause at
least two VM-EXIT. So we currently only imperilment vPMEM in this patchset

--- vPMEM design ---
We introduce a new device named "pc-nvdimm", it has a parameter, file, which
is the file-based backed memory passed to guest. The file can be regular file
and block device. We can use any file when we do test or emulation, however,
in the real word, the files passed to guest are:
- the regular file in the filesystem with DAX enabled created on NVDIMM device
  on host
- the raw PMEM device on host, e,g /dev/pmem0
Memory access on the address created by mmap on these kinds of files can
directly reach NVDIMM device on host.

--- vConfigure data area design ---
Each NVDIMM device has a configure data area which is used to store label
namespace data. In order to emulating this area, we divide the file into two
parts:
- first parts is (0, size - 128K], which is used as PMEM
- 128K at the end of the file, which is used as Config Data Area
So that the label namespace data can be persistent during power lose or system
failure

--- _DSM method design ---
_DSM in ACPI is used to configure NVDIMM, currently we only allow access of
label namespace data, i.e, Get Namespace Label Size (Function Index 4),
Get Namespace Label Data (Function Index 5) and Set Namespace Label Data
(Function Index 6)

_DSM uses two pages to transfer data between ACPI and Qemu, the first page
is RAM-based used to save the input info of _DSM method and Qemu reuse it
store output info and another page is MMIO-based, ACPI write data to this
page to transfer the control to Qemu

We use the address region above 4G to map these pages because there is huge
free space above 4G and it can avoid the address overlap with PCI and other
address reserved component (e,g HPET). This is also the reason we choose MMIO
notification instead of PIO

====== Test ======
In host
1) create memory backed file, e.g # dd if=zero of=/tmp/nvdimm bs=1G count=10
2) append '-device pc-nvdimm,file=/tmp/nvdimm' in Qemu command line

In guest, download the latest upsteam kernel (4.2 merge window) and enable
ACPI_NFIT, LIBNVDIMM and BLK_DEV_PMEM.
1) insmod drivers/nvdimm/libnvdimm.ko
2) insmod drivers/acpi/nfit.ko
3) insmod drivers/nvdimm/nd_btt.ko
4) insmod drivers/nvdimm/nd_pmem.ko
You can see the whole nvdimm device used as a single namespace and /dev/pmem0
appears. You can do whatever on /dev/pmem0 including DAX access.

Currently Linux NVDIMM driver does not support namespace operation on this
kind of PMEM, apply below changes to support dynamical namespace:

@@ -798,7 +823,8 @@ static int acpi_nfit_register_dimms(struct acpi_nfit_desc *a
                        continue;
                }
 
-               if (nfit_mem->bdw && nfit_mem->memdev_pmem)
+               //if (nfit_mem->bdw && nfit_mem->memdev_pmem)
+               if (nfit_mem->memdev_pmem)
                        flags |= NDD_ALIASING;

You can append another NVDIMM device in guest and do:                       
# cd /sys/bus/nd/devices/
# cd namespace1.0/
# echo `uuidgen` > uuid
# echo `expr 1024 \* 1024 \* 128` > size
then reload nd.pmem.ko

You can see /dev/pmem1 appears

====== TODO ======
1) NVDIMM NUMA support
2) NVDIMM hotplug support

Xiao Guangrong (16):
  acpi: allow aml_operation_region() working on 64 bit offset
  i386/acpi-build: allow SSDT to operate on 64 bit
  acpi: add aml_derefof
  acpi: add aml_sizeof
  acpi: add aml_create_field
  pc: implement NVDIMM device abstract
  nvdimm: reserve address range for NVDIMM
  nvdimm: init backend memory mapping and config data area
  nvdimm: build ACPI NFIT table
  nvdimm: init the address region used by _DSM method
  nvdimm: build ACPI nvdimm devices
  nvdimm: save arg3 for NVDIMM device _DSM method
  nvdimm: support NFIT_CMD_IMPLEMENTED function
  nvdimm: support NFIT_CMD_GET_CONFIG_SIZE function
  nvdimm: support NFIT_CMD_GET_CONFIG_DATA
  nvdimm: support NFIT_CMD_SET_CONFIG_DATA

 hw/acpi/aml-build.c         |   32 +-
 hw/i386/acpi-build.c        |    9 +-
 hw/i386/acpi-dsdt.dsl       |    2 +-
 hw/i386/pc.c                |   11 +-
 hw/mem/Makefile.objs        |    1 +
 hw/mem/pc-nvdimm.c          | 1040 +++++++++++++++++++++++++++++++++++++++++++
 include/hw/acpi/aml-build.h |    5 +-
 include/hw/mem/pc-nvdimm.h  |   56 +++
 8 files changed, 1149 insertions(+), 7 deletions(-)
 create mode 100644 hw/mem/pc-nvdimm.c
 create mode 100644 include/hw/mem/pc-nvdimm.h

-- 
2.1.0