Seamless Kernel Upgrade in Cloud Environment · Pull Request !412 · openEuler/kernel

This PR is a POC code demo for Seamless Kernel Upgrade (VMM Fast Restart) in cloud environment.

## Description
Frequent security and other fixes require CSPs (Cloud Service Providers) to reset their platforms more often, which results in more downtime to their customers.

It is desirable to support fast restart of system including kernel and Qemu in cloud environment.

Community already have some solutions, however they have some limitations:
- Live patching is OK for small fixes (no service downtime), but failure rate is high for big changes
- VM live migration is a stable feature in most VMMs (<1s service downtime), however with limitations, for example, it has poor support for passthrough devices. It also requires hardware resources such as space machine to migrate VM into. Meanwhile, there maybe infrastructure-imposed failures such as network configuration changes during migration.

Seamless System Live Update is an alternative option for the OS/VMM Live update.
- It supports passthrough devices.
- It aims to be seamless (invisible) to guest VMs.
- It aims to achieve several-second time level for both Qemu and Kernel live update.

Seamless System Live Update achieves its goal with following approaches:
- Leverages kexec reboot to bypass firmware reboot, so it saves reboot time.
- It also seamlessly save/restore guest VM state directly to/from memory, because kexec reboot doesn't reset memory. 
- The state of the passthrough devices is seamlessly saved/restored across the reboot
- Passthrough devices are kept alive across the reboot. Interrupts and DMA operations keep alive in these devices during the reboot.

## More Details:
        https://github.com/x48Jason/doc/blob/master/VMM_Fast_Restart-openEuler.pdf

## POC Repos
POC code repo and branch can be found at:
	- https://gitee.com/x56Jason/vmmfr-linux/tree/vmmfr-2209/
	- https://gitee.com/x56Jason/vmmfr-qemu/tree/vmmfr-qemu/
	- https://github.com/intel/vmm-fast-restart-kexec/tree/vmm-fast-restart
	
## openEuler Kernel Issue
#I645RP

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