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Setting up NVDIMM Emulation for Assise

Check kernel supports emulation

Emulation is supported by the kernel versions 4.0+ but it is recommended to use versions higher then 4.2 due to ease of configuration.

Getting the kernel source

Get the current kernel version using uname version.

uname -r
5.6.0-2-amd64

Download the kernel source files. For systems with apt-get, you can do so as follows:

sudo apt-get install linux-source-5.6
cp /usr/src/linux-sources-5.6.tar.xz
tar xf linux-sources-5.6.tar.xz
cd linux-sources-5.6

Enabling features

make nconfig

Mark these features as enabled by pressing y. Save the configuration by pressing the escape key.

Processor type and features --->
	[*] Support non-standard NVDIMMs and ADR protected memory
File systems --->
	[*] Direct Access (DAX) support

Also change the .config file and set:

CONFIG_SYSTEM_TRUSTED_KEYS = ""

Installing new kernel

Then make the kernel and install it. The kernel build will be in the directory above the sources directory.

make deb-pkg
sudo dpkg -i linux-image.x.y.z.deb 
sudo shutdown -r now

Setting up kernel parameters

To find the proper kernel parameters, you need to find the set of available memory regions. You can do so by running the following command: dmesg | grep BIOS-e820

[    0.000000] BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000053fffffff] usable

Pick a region of memory that is marked as usable. e.g.

[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000053fffffff] usable

The region above starts at 0x0000000100000000 (4 GB) and ends at 0x000000053fffffff (21 GB). We can configure our machine to create a pmem memory region by passing the following kernel parameters:

memmap=8G!4G

This will reserve 8 GB of memory starting at the 4 GB offset (which is usable in this example). On an Ubuntu 18.04 BIOS machine, you can pass these parameters by modifying the grub configuration file.

vi /etc/default/grub
GRUB_CMDLINE_LINUX="memmap=8G!4G"

After editing this file, run the following command to apply your changes:

update-grub2 && update-grub

After rebooting, you should see one pmem region configured.

ndctl list

[
{
  "dev":"namespace1.0",
"mode":"fsdax",
"map":"mem",
"size":8589934592,
"sector_size":512,
"blockdev":"pmem0"
} 
]

More info

Choosing pmem kernel parameters