VPID

VPID stands for Virtual Processor Identifier in the context of computer virtualization. It is a hardware-assisted mechanism used by some x86 processors to tag translation lookaside buffer (TLB) entries with a per-virtual-processor identifier. This tagging allows the processor to maintain separate TLB entries for different virtual CPUs, reducing the frequency and cost of global TLB flushes during VM context switches and helping to improve performance for guest operating systems running on hardware-assisted virtualization.

Hardware and software support: VPID support is provided on many Intel processors as part of virtualization features associated with VT-x and related technologies. Hypervisors such as KVM, VMware, Hyper-V, and Xen leverage VPID to minimize TLB invalidations when switching between virtual CPUs. When a VM is scheduled on a vCPU, the hypervisor assigns a VPID to that vCPU; TLB entries are created with that VPID, allowing targeted invalidation. The INVVPID instruction is used to invalidate TLB entries associated with a specific VPID, rather than flushing the entire TLB.

Limitations and notes: Not all processors implement VPID, and some older hardware relies on more general TLB management without per-VM tagging. Effective use of VPID depends on processor support, firmware, and hypervisor implementation. Correct operation also requires coordination between the hypervisor and the CPU’s paging and virtualization mechanisms to ensure consistency of memory translations across VM context switches.

Other uses: The acronym VPID can appear in different technical contexts, sometimes standing for phrases other than Virtual Processor Identifier in vendor documentation or domain-specific materials. In the virtualization field, however, VPID most commonly refers to Virtual Processor Identifier.