vm - hypervisor / virtual-machine detection

Header: kernel/include/kernel/vm.h Source: arch/i386/core/vm.c

Identifies the platform Makar is running on so drivers can apply VM-specific quirks — Hyper-V’s PS/2 mouse Y convention, per-hypervisor IDE DMA policy, framebuffer paths. Detection is best-effort, runs once at boot (vm_detect(), after the PCI scan so it can use bus signals), and the result is cached. This is the seam the conventions call fallback-gating: a quirk keys off vm_kind() and the tested QEMU path is never disturbed.

Detection method

CPUID.1:ECX[31] is the “hypervisor present” bit.
CPUID leaf 0x40000000 returns a 12-byte vendor signature identifying the hypervisor interface: Microsoft Hv, VMwareVMware, VBoxVBoxVBox, KVMKVMKVM, TCGTCGTCGTCG (QEMU/TCG), XenVMMXenVMM.
QEMU is confirmed via its fw_cfg device (port 0x510/0x511 signature QEMU), distinguishing QEMU (incl. QEMU+KVM) from a bare KVM host.
Bochs has no hypervisor CPUID leaf; it’s identified by the Bochs/DISPI VBE id at port 0x1CE/0x1CF when no other hypervisor was found.

API

Function	Role
`vm_detect()`	Probe the platform and cache the result. Call once, early in boot.
`vm_kind()`	The detected platform (`VM_BAREMETAL` until `vm_detect` runs).
`vm_name()`	A short lowercase name (`"qemu"`, `"hyperv"`, `"bare metal"`…) for boot logs / `/proc`. Never `NULL`.

`enum vm_kind`

VM_BAREMETAL, VM_QEMU, VM_KVM, VM_BOCHS, VM_HYPERV, VM_VIRTUALBOX, VM_VMWARE, VM_XEN, VM_UNKNOWN_HV (hypervisor present, vendor unrecognised).

The detected name appears on the boot console (Virtualization: <name>) and in /proc/cpuinfo via procfs.