On Mon, 15 Jun 2020 15:41:54 -0600
"Edmund F. Nadolski" <edmund.f.nadol...@gmail.com> wrote:
> Hi,
> 
> I'm a noob to VFIO so hopefully this is not to lame a question.
> 
> I'm looking to set up a Linux guest VM with a direct-assigned nvme ssd, 
> that I can control by a usermode driver with VFIO.  I enable nested 
> virtualization in KVM and set up the iommu parameters on the command line:
> 
> Host:
> # dmesg | grep Command
> [    0.000000] Command line: BOOT_IMAGE=(hd0,msdos1)/vmlinuz-5.7.0_0611+ 
> root=UUID=<blah> ro resume=UUID=<blah> console=tty0 console=ttyS4,115200 
> intel_iommu=on iommu=pt
> # modprobe kvm_intel nested=1
> # ls /sys/kernel/iommu_groups
> 0  1  10  11  12  13  14  15  16  17  18  19  2  3  4  5  6  7  8  9
> 
> 
> The direct assignment works and I can see the drive in the guest, but 
> vfio does not create any iommu groups:
> 
> Guest:
> # lspci | grep Non
> 07:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe 
> SSD Controller SM981/PM981/PM983
> # dmesg | grep -i -e DMAR -e IOMMU
> [    0.000000] Command line: BOOT_IMAGE=(hd0,msdos1)/vmlinuz-5.7.0 
> root=/dev/mapper/fedora_localhost--live-root ro 
> resume=/dev/mapper/fedora_localhost--live-swap 
> rd.lvm.lv=fedora_localhost-live/root 
> rd.lvm.lv=fedora_localhost-live/swap intel_iommu=on iommu=pt
> [    0.064051] Kernel command line: 
> BOOT_IMAGE=(hd0,msdos1)/vmlinuz-5.7.0 
> root=/dev/mapper/fedora_localhost--live-root ro 
> resume=/dev/mapper/fedora_localhost--live-swap 
> rd.lvm.lv=fedora_localhost-live/root 
> rd.lvm.lv=fedora_localhost-live/swap intel_iommu=on iommu=pt
> [    0.064102] DMAR: IOMMU enabled
> [    0.383193] iommu: Default domain type: Passthrough (set via kernel 
> command line)
> [    1.467722]     intel_iommu=on
> # ls -la /sys/kernel/iommu_groups/
> total 0
> drwxr-xr-x.  2 root root 0 Jun 15 15:16 .
> drwxr-xr-x. 15 root root 0 Jun 15 15:12 ..
> #
> 
> Clearly I'm missing something in my setup/config, but I'm not sure that 
> that could be.  Can anyone please advise?

There needs to be an intel-iommu device in the VM configuration or else
the intel_iommu=on option to the guest kernel will only print that
enabled line and does nothing more.

https://wiki.qemu.org/Features/VT-d

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