virtualization-cpu

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FAQ

Intel vt-x vs vt-d

VT-x is CPU virtualization technology from intel, while VT-d is IO virtualization technology from intel as well.

  • VT-x which supports root mode and vmx mode for cpu and series of instructions for use to support cpu virtualization.
  • VT-d(Intel® Virtualization Technology for Directed I/O) is technology which supports IOMMU, hence can provide Direct/IO, IO passthrough to guest VM.

How to enable vt-x and vt-d

If you CPU supports these, there is a switch in BIOS to enable/disable them, the switch is mostly located at Processor tab.

check VT-x enabled or not

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# vmx Virtual Machine Extensions
$ lscpu | grep vmx
Flags:                 fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb cat_l3 cdp_l3 intel_pt tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm cqm rdt_a rdseed adx smap xsaveopt cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm ida arat pln pts

check VT-d enabled or not
When vt-d is enable and IOMMU kernel is loaded, at system boot time, IOMMU is initialized

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# centos7
$ dmesg | grep "DMAR:"
[    0.000000] DMAR: IOMMU enabled
...