Check if VT-D / IOMMU has been enabled in the BIOS/UEFI

If VT-d is enabled, Linux will configure DMA Remapping at boot time. The easiest way to find this is to look in dmesg for DMAR entries. If you don't see errors, then VT-d is enabled.

For example:

[root@localhost ~]# dmesg | grep DMAR[    0.000000] ACPI: DMAR 0x00000000BBECB000 0000A8 (v01 LENOVO TP-R0D   00000930 PTEC 00000002)[    0.001000] DMAR: Host address width 39[    0.001000] DMAR: DRHD base: 0x000000fed90000 flags: 0x0[    0.001000] DMAR: dmar0: reg_base_addr fed90000 ver 1:0 cap 1c0000c40660462 ecap 19e2ff0505e[    0.001000] DMAR: DRHD base: 0x000000fed91000 flags: 0x1[    0.001000] DMAR: dmar1: reg_base_addr fed91000 ver 1:0 cap d2008c40660462 ecap f050da[    0.001000] DMAR: RMRR base: 0x000000bbdd8000 end: 0x000000bbdf7fff[    0.001000] DMAR: RMRR base: 0x000000bd000000 end: 0x000000bf7fffff[    0.001000] DMAR-IR: IOAPIC id 2 under DRHD base  0xfed91000 IOMMU 1[    0.001000] DMAR-IR: HPET id 0 under DRHD base 0xfed91000[    0.001000] DMAR-IR: Queued invalidation will be enabled to support x2apic and Intr-remapping.[    0.002000] DMAR-IR: Enabled IRQ remapping in x2apic mode

Another example with x2apic opt out:

[root@localhost ~]# dmesg | grep DMAR[    0.000000] ACPI: DMAR 0000000079a20300 000C4 (v01 SUPERM SMCI--MB 00000001 INTL 20091013)[    0.106389] DMAR: Host address width 46[    0.106392] DMAR: DRHD base: 0x000000fbffc000 flags: 0x1[    0.106400] DMAR: dmar0: reg_base_addr fbffc000 ver 1:0 cap 8d2078c106f0466 ecap f020de[    0.106402] DMAR: RMRR base: 0x0000007bb24000 end: 0x0000007bb32fff[    0.106404] DMAR: ATSR flags: 0x0[    0.106407] DMAR: RHSA base: 0x000000fbffc000 proximity domain: 0x0[    0.106409] DMAR-IR: IOAPIC id 8 under DRHD base  0xfbffc000 IOMMU 0[    0.106411] DMAR-IR: HPET id 0 under DRHD base 0xfbffc000[    0.106413] DMAR-IR: x2apic is disabled because BIOS sets x2apic opt out bit.[    0.106414] DMAR-IR: Use 'intremap=no_x2apic_optout' to override the BIOS setting.[    0.106591] DMAR-IR: Enabled IRQ remapping in xapic mode

Either way, you're looking for that last line, DMAR-IR: Enabled IRQ remapping in <whichever> mode.

On a system with VT-d disabled, you will either see an error message, or nothing at all.

[root@localhost ~]# dmesg | grep DMAR[root@localhost ~]#

I just found another way that seems to work even if the iommu kernel parameters have not been set:

if compgen -G "/sys/kernel/iommu_groups/*/devices/*" > /dev/null; then    echo "AMD's IOMMU / Intel's VT-D is enabled in the BIOS/UEFI."else    echo "AMD's IOMMU / Intel's VT-D is not enabled in the BIOS/UEFI"fi

Building on Jo-Erlend Schinstad's answer:

Install cpu-checker

$ sudo apt-get update$ sudo apt-get install cpu-checker

Then check:

$ kvm-ok

If the CPU is enabled, you should see something like:

INFO: /dev/kvm existsKVM acceleration can be used

Otherwise, you might see something like:

INFO: /dev/kvm does not existHINT:   sudo modprobe kvm_intelINFO: Your CPU supports KVM extensionsINFO: KVM (vmx) is disabled by your BIOSHINT: Enter your BIOS setup and enable Virtualization Technology (VT),      and then hard poweroff/poweron your systemKVM acceleration can NOT be used