Re: Query on IOMMU

[Chris Wright <chrisw@sous-sol.org>]

* Prasad Joshi (P.G.Joshi@student.reading.ac.uk) wrote:
> I am facing a problem with enabling the IOMMU.
> 
> Dec 21 15:50:57 prasad-kvm kernel: [    0.000000] Aperture pointing to e820 RAM. Ignoring.
> Dec 21 15:50:57 prasad-kvm kernel: [    0.000000] Your BIOS doesn't leave a aperture memory hole
> Dec 21 15:50:57 prasad-kvm kernel: [    0.000000] Please enable the IOMMU option in the BIOS setup
> 
> Dec 21 15:50:57 prasad-kvm kernel: [    2.790913] pci 0000:01:05.0: Firmware left e100 interrupts enabled; disabling
> Dec 21 15:50:57 prasad-kvm kernel: [    2.791941] pci 0000:00:00.2: PCI INT A -> GSI 55 (level, low) -> IRQ 55
> Dec 21 15:50:57 prasad-kvm kernel: [    2.792775] AMD-Vi: Enabling IOMMU at 0000:00:00.2 cap 0x40
> Dec 21 15:50:57 prasad-kvm kernel: [    2.800989] AMD-Vi: Lazy IO/TLB flushing enabled
> 
> 
> I have enabled IOMMU in the BIOS, but I am not sure why it is still asking to enabled IOMMU in BIOS. Do I need to worry about this?

It's unfortunate wording.  It's telling you that the GART is missing,
which is fine because you have an IOMMU.

> Besides I don't see the DMAR message similar to the one mentioned on the link 
> http://www.linux-kvm.org/page/How_to_assign_devices_with_VT-d_in_KVM

That wiki page is specific to Intel VT-d.  You have an AMD box with IOMMU,
so all looks fine.

Are you interested in using the IOMMU to do direct PCI device assignment
to a guest?

thanks,
-chris