how-to: Add how-to for Kata Containers with virtio-mem

Add how-to for Kata Containers with virtio-mem.

Fixes: kata-containers#591

Signed-off-by: Hui Zhu <[email protected]>

Author: teawater

how-to/README.md

@@ -23,3 +23,4 @@
 - [What Is VM Templating and How To Enable It](what-is-vm-templating-and-how-do-I-use-it.md)
 - [Privileged Kata Containers](privileged.md)
 - [How to load kernel modules in Kata Containers](how-to-load-kernel-modules-with-kata.md)
+- [How to use Kata Containers with `virtio-mem`](how-to-use-virtio-mem-with-kata.md)

how-to/how-to-use-virtio-mem-with-kata.md

@@ -0,0 +1,53 @@
+# Kata Containers with `virtio-mem`
+
+- [Introduction](#introduction)
+- [Requisites](#requisites)
+- [Run a Kata Container utilizing `virtio-mem`](#run-a-kata-container-utilizing-virtio-mem)
+
+## Introduction
+
+The basic idea of `virtio-mem` is to provide a flexible, cross-architecture memory hot plug and hot unplug solution that avoids many limitations imposed by existing technologies, architectures, and interfaces.
+More details can be found in https://lkml.org/lkml/2019/12/12/681.
+
+Kata Containers with `virtio-mem` supports memory resize.
+
+## Requisites
+
+Kata Containers with `virtio-mem` requires Linux and the QEMU that support `virtio-mem`.
+The Linux kernel and QEMU upstream version still not support `virtio-mem`.  @davidhildenbrand is working on them.
+Please use following unofficial version of the Linux kernel and QEMU that support `virtio-mem` with Kata Containers.
+
+The Linux kernel is at https://github.com/davidhildenbrand/linux/tree/virtio-mem-rfc-v4.
+The Linux kernel config that can work with Kata Containers is at https://gist.github.com/teawater/016194ee84748c768745a163d08b0fb9.
+
+The QEMU is at https://github.com/teawater/qemu/tree/kata-virtio-mem. (The original source is at https://github.com/davidhildenbrand/qemu/tree/virtio-mem.  Its base version of QEMU cannot work with Kata Containers.  So merge the commit of `virtio-mem` to upstream QEMU.)
+
+Set Linux and the QEMU that support `virtio-mem` with following line in the Kata Containers QEMU configuration `configuration-qemu.toml`:
+```toml
+[hypervisor.qemu]
+path = "qemu-dir"
+kernel = "vmlinux-dir"
+```
+
+Enable `virtio-mem` with following line in the Kata Containers configuration:
+```toml
+enable_virtio_mem = true
+```
+
+## Run a Kata Container utilizing `virtio-mem`
+
+Use following command to enable memory overcommitment of a Linux kernel.  Because QEMU `virtio-mem` device need to allocate a lot of memory.
+```
+$ echo 1 | sudo tee /proc/sys/vm/overcommit_memory
+```
+
+Use following command start a Kata Container.
+```
+$ docker run --rm -it --runtime=kata --name test busybox
+```
+
+Use following command set the memory size of test to default_memory + 512m.
+```
+$ docker update -m 512m --memory-swap -1 test
+```
+