Enable IOMMU Inside QEMU

[Alok Prasad]

How Can i i enable vIOMMU inside QEMU

Have run the qemu with below parameters.

root@beta-hp-p70:/home/fastlinq/alok/KVM-VM# ps -ef | grep qemu
root     20347     1  2 06:06 ?        00:00:36 /usr/bin/qemu-system-x86_64 -name guest=centos7_8_vm,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-15-centos7_8_vm/master-key.aes -machine pc-q35-4.2,accel=kvm,usb=off,dump-guest-core=off,kernel_irqchip=split -cpu SandyBridge,vmx=on -m 4096 -realtime mlock=off -smp 1,sockets=1,cores=1,threads=1 -uuid f8ee6a5e-6253-453c-8304-7eca50fa7b94 -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-15-centos7_8_vm/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -no-acpi -boot strict=on -device intel-iommu,intremap=on,caching-mode=on -device pcie-root-port,port=0x10,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x2 -device pcie-root-port,port=0x11,chassis=2,id=pci.2,bus=pcie.0,addr=0x2.0x1 -device pcie-root-port,port=0x12,chassis=3,id=pci.3,bus=pcie.0,addr=0x2.0x2 -device pcie-root-port,port=0x13,chassis=4,id=pci.4,bus=pcie.0,addr=0x2.0x3 -device pcie-root-port,port=0x14,chassis=5,id=pci.5,bus=pcie.0,addr=0x2.0x4 -device pcie-root-port,port=0x15,chassis=6,id=pci.6,bus=pcie.0,addr=0x2.0x5 -device pcie-root-port,port=0x16,chassis=7,id=pci.7,bus=pcie.0,addr=0x2.0x6 -device pcie-root-port,port=0x17,chassis=8,id=pci.8,bus=pcie.0,addr=0x2.0x7 -device qemu-xhci,id=usb,bus=pci.5,addr=0x0 -device virtio-serial-pci,id=virtio-serial0,bus=pci.3,addr=0x0 -drive file=/home/fastlinq/centos-7.8.qcow2,format=qcow2,if=none,id=drive-virtio-disk0 -device virtio-blk-pci,scsi=off,bus=pci.4,addr=0x0,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -drive file=/home/fastlinq/dev.img,format=raw,if=none,id=drive-virtio-disk2,cache=none,aio=native -device virtio-blk-pci,scsi=off,bus=pci.8,addr=0x0,drive=drive-virtio-disk2,id=virtio-disk2 -netdev tap,fd=26,id=hostnet0 -device rtl8139,netdev=hostnet0,id=net0,mac=52:54:00:b8:d3:f8,bus=pci.2,addr=0x0 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -vnc 127.0.0.1:0 -device cirrus-vga,id=video0,bus=pcie.0,addr=0x1 -device virtio-balloon-pci,id=balloon0,bus=pci.6,addr=0x0 -msg timestamp=on

XML of the same ( ony relevant part)

  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='x86_64' machine='pc-q35-4.2'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <kvm>
      <hidden state='off'/>
    </kvm>
    <ioapic driver='qemu'/>
  </features>
  <cpu mode='custom' match='exact' check='partial'>
    <model fallback='allow'>SandyBridge</model>
    <feature policy='require' name='vmx'/>
  </cpu>

...

....

 <iommu model='intel'>
      <driver intremap='on' caching_mode='on'/>
    </iommu>

and in Guest VM 

[root@centos-8 ~]# dmesg | grep DMAR
[    0.000000] DMAR: IOMMU enabled

[root@centos-8 ~]# cat /proc/cmdline
BOOT_IMAGE=(hd0,gpt2)/vmlinuz-4.18.0-193.6.3.el8_2.x86_64 root=UUID=4fd120e4-1f6d-46b3-a404-5569ef6af1f9 ro console=tty0 rd_NO_PLYMOUTH crashkernel=auto resume=UUID=40f14688-2619-4046-a9eb-b7333fff1b84 console=ttyS0,115200 intel_iommu=on

I don't see other Prints related to IOMMU which seems that its not present in guest VM.

ideally i should see some other prints 

dmesg | grep -e DMAR -e IOMMU
[ 0.000000] ACPI: DMAR 0x000000003E86C000 000048 (v01 BOCHS BXPCDMAR 00000001
BXPC 00000001)
[ 0.000000] DMAR: IOMMU enabled ---> only shows that its enabled in OS/GRUB
[ 0.145746] DMAR: Host address width 39
[ 0.145747] DMAR: DRHD base: 0x000000fed90000 flags: 0x1
[ 0.145769] DMAR: dmar0: reg_base_addr fed90000 ver 1:0 cap 12008c22260286 ecap
f00f5a
[ 0.145776] DMAR: No RMRR found
[ 0.145776] DMAR: No ATSR found
[ 0.145825] DMAR: dmar0: Using Queued invalidation
[ 0.218192] DMAR: Setting RMRR:
[ 0.218193] DMAR: Prepare 0-16MiB unity mapping for LPC
[ 0.219038] DMAR: Setting identity map for device 0000:00:1f.0 [0x0 - 0xffffff]
[ 0.257194] DMAR: Intel(R) Virtualization Technology for Directed I/O

root@beta-hp-p70:/home/fastlinq/alok/KVM-VM# /usr/bin/qemu-system-x86_64 --version
QEMU emulator version 4.2.1
Copyright (c) 2003-2019 Fabrice Bellard and the QEMU Project developers

I am missing here something,? 

Thanks,

Alok