Hypervisor Architecture
A hypervisor lets several virtual machines share one physical computer while keeping each guest operating system isolated. Its architecture controls CPU execution, memory translation, interrupts, and device access between guests and hardware.
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Don't Panic
Don't Panic - Hypervisor Architecture
A hypervisor, or virtual machine monitor, creates virtual machines and controls their access to physical hardware. Each guest sees virtual processors, memory, interrupts, and devices while the hypervisor preserves isolation and schedules shared resources. The guest behaves as though it owns a computer; the hypervisor decides which resources are real, shared, or emulated.
Most ordinary guest instructions execute directly on the physical CPU. Hardware virtualization adds a guest mode and a control structure per virtual CPU. On Intel, VMX uses VM-entry and VM-exit transitions; AMD SVM provides analogous controls. The hypervisor selects events that must trap: privileged register access, selected instructions, interrupts, or device access. Each exit saves guest state, lets the hypervisor emulate or delegate work, then resumes the guest. Exits are the control points that also cost cycles, so a sound design traps only what isolation requires.
The architecture is larger than the privileged core. Device models, host drivers, firmware, and a management plane may share a process, run separately, live in a management partition, or move onto dedicated hardware. Placement changes performance, failure domains, and attack surface. Nested virtualization adds another layer of exits when a guest itself runs a hypervisor, which is useful for labs and some clouds and expensive when unused.
A working mental model separates CPU virtualization, memory and interrupt virtualization, and device emulation. CPU scheduling fixes do not repair a chatty virtual device. Profile exit reasons before rewriting the guest workload.
Read the Intro for the execution boundary and CPU virtualization model. Use the Cheatsheet when you need the exit and device-model maps. Landscape and Timeline place hypervisor designs among related virtualization technologies.
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Sources
- https://docs.aws.amazon.com/whitepapers/latest/security-design-of-aws-nitro-system/traditional-virtualization-primer.html
Supports
- Defines hosts, guests, VMMs, native guest execution, intercepted privileged operations, device models, and privileged management operating systems.
- https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html
Supports
- Documents VMX operation, VM entry, VM exit, execution controls, interrupt virtualization, EPT, and processor state virtualization.
- https://docs.amd.com/v/u/en-US/40332_4.09_APM_PUB
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- Documents Secure Virtual Machine operation, intercepts, virtual machine state, and nested paging on AMD64 processors.
- https://docs.kernel.org/virt/kvm/api.html
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- Documents KVM virtual machine and vCPU creation, guest-memory mapping, vCPU execution, exits, and user-space interaction.
- https://www.qemu.org/docs/master/system/introduction.html
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- Explains system emulation, accelerators, device models, and QEMU's relationship with KVM.
- https://learn.microsoft.com/en-us/windows-server/virtualization/hyper-v/architecture
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- Documents Hyper-V partitions, the root partition, virtual processors, memory isolation, VMBus, synthetic devices, and IOMMU use.
- https://docs.kernel.org/driver-api/vfio.html
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- Documents secure user-space device access, IOMMU isolation, device groups, DMA mappings, and reset concerns.
- https://libvirt.org/migration.html
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- Documents migration flows, hypervisor connections, shared and non-shared storage, and network requirements.
- https://docs.aws.amazon.com/whitepapers/latest/security-design-of-aws-nitro-system/the-nitro-system-journey.html
Supports
- Documents the 2017 C5 milestone, removal of domain zero, KVM-based minimized VMM, and I/O offload to Nitro Cards.
- https://docs.aws.amazon.com/whitepapers/latest/security-design-of-aws-nitro-system/the-components-of-the-nitro-system.html
Supports
- Documents Nitro Controller, Nitro Cards, hypervisor responsibilities, SR-IOV assignment, minimized services, and control-plane separation.
- https://www.vm.ibm.com/history/vm40hist.pdf
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- Records the CP-67 lineage beginning in 1966 and the VM/370 release in August 1972.
- https://doi.org/10.1145/361011.361073
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- Records the 1974 formal model for virtual machine monitors and its resource-control, equivalence, and efficiency properties.
- https://dl.acm.org/doi/10.1145/96267.96279
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- Grounds the software techniques that made x86 virtualization practical before processor virtualization extensions.
- https://www.cl.cam.ac.uk/research/srg/netos/papers/2003-xensosp.pdf
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- Documents Xen's 2003 paravirtualized architecture, domains, resource management, and performance goals.
- https://www.kernel.org/doc/ols/2007/ols2007v1-pages-225-230.pdf
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- Documents KVM's integration of hardware virtualization into Linux and its availability with Linux 2.6.20.
- https://news.microsoft.com/source/2008/03/19/microsoft-reaches-virtualization-milestone-with-release-candidate-of-hyper-v/
Supports
- Records Hyper-V as hypervisor-based virtualization software for Windows Server 2008 and its 2008 release-candidate milestone.
- https://github.com/sindresorhus/awesome
Supports
- Provides the required starting point for awesome-list discovery.
- https://github.com/Wenzel/awesome-virtualization
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- Identifies Firecracker, Cloud Hypervisor, crosvm, ACRN, Bareflank, mainstream hypervisors, research papers, and processor-virtualization chronology.
- https://github.com/firecracker-microvm/firecracker/blob/main/docs/design.md
Supports
- Documents Firecracker's KVM boundary, per-microVM process, vCPU threads, narrow device model, shared queues, and sandboxing.
- https://www.cloudhypervisor.org/docs/
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- Documents the project's cloud-workload VMM, KVM requirements, virtual devices, boot paths, and control interface.
- https://crosvm.dev/
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- Describes a hosted VMM that runs untrusted guests and isolates virtual devices in separate sandboxes.
- https://projectacrn.github.io/latest/developer-guides/hld/index.html
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- Documents the type 1 hypervisor, Service VM, User VMs, CPU and memory virtualization, interrupt handling, and I/O models.
- https://bareflank.github.io/hypervisor/
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- Describes an SDK and examples for prototyping hypervisor extensions and VMX-root behavior.
- https://www.vmware.com/products/cloud-infrastructure/vsphere
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- Grounds VMware vSphere and ESXi as a server virtualization platform with a bare-metal hypervisor and centralized management.
- https://www.proxmox.com/en/products/proxmox-virtual-environment/overview
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- Documents a virtualization platform that manages KVM virtual machines with clustering, storage, networking, and migration services.
- https://www.nutanix.com/products/ahv
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- Documents AHV's placement inside the Nutanix infrastructure stack and its VM lifecycle and management role.
- https://www.virtualbox.org/manual/UserManual.html
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- Documents a hosted cross-platform VMM, virtual hardware, guest additions, networking, storage, and snapshots.
- https://xenproject.org/
Supports
- Grounds Xen as an open-source type 1 hypervisor with a privileged control domain and multiple guest types.
- https://docs.xcp-ng.org/
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- Documents a Xen-based virtualization platform, XAPI management stack, storage, networking, and migration operations.
- https://www.redhat.com/en/technologies/cloud-computing/openshift/virtualization
Supports
- Documents KVM-based virtual machines managed alongside container workloads through Kubernetes control-plane resources.