Day-4
Hypervisor
A physical computer system can build multiple virtual computer system with its own virtual resources. Just like apps in U-level, each virtual system will consider themselves uniquely occupies these resources.
Emulator like a interpretor to stimulate a virtual system while in loose demand of efficiency.
Hypervisor will execute most instructions directly as a isomorphism of the stimulated virtual system to gain a huge efficiency.
*I type: Each virtual OS is equal on hardware.
*II type: Virtual OS is on host OS.
Each instance as Guest(OS Image) be loaded on our host os kernel.
Design
Only focus on hypervisor(I type).
Levels are extended, because we need to separate host and guest, so U-Level become U, VU-Level. So does the kernel level because we need to separate host, the hypervisor and guest, the virtual OS. So S-Level become HS, VS-Level.
Communication
Instructions will be implemented in communication of HS and VS, when there’s a sbi-call, VS will communicate HS to implement.
In hstatus of RISC-V, design the virtualization mode:
SPV: the source of HS or VS, which determines the sret to VU or U.SPVP: the permission of modification of memory that HS to V.
We need to store guest context and host context, then switch between ret(VM-Exit) and sret. We implement this by run_guest and guest_exit which both is the other’s reverse.
Timer will be injected to sbi-call by setting a virtual clock in VS, when set timer, we clear timer of guest and set timer of host; when interrupt, we set clear timer of host and set timer of guest waiting for next request of timer.
Memory will be separated based on guest and host too. GVA will be a map of GPA as guest memory. However, HPA take responsibility of handle GPA as the virtualization process.
Dev will record each start vaddr and when VM-Exit of PageFault, it will findvmdevs.find(addr) and call handle_mmio for corresponding request.