Re: Any side effect if turn off amd_iommu

[Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>]

Hi AceLan Kao,

On Wed, May 13, 2015 at 03:37:57PM +0800, AceLan Kao wrote:
> The method I described is not making any guess, we need a table to
> write down the correct ioapic value for those machines, we can add the
> BIOS version check(DMI_BIOS_VERSION) if you think the behavior may
> change with different version of BIOSes.

You don't know which IO-APIC is which one without a correct IVRS table.
AMD desktop systems have usually have up to two IO-APICs, one in the SB
and one in the NB. But the ids of these IO-APICs are not fixed and
can depend on the BIOS version as well as on the processor that is
plugged into the board. So since we don't know which IO-APIC is which
one we can't make any good guesses that work for everybody. When we
implement workarounds we may fix it for one user, but risk breakage for
others.

> If you still feel uncomfortable, I'm okay with any solutions, but I
> don't get it how to do it in your way.
> We can found those machines from bug reports(I have some machines on
> my hand, too), so we need a table to record those machines? And how to
> disable interrupt remapping, will it lead to any side effect?

Disabling interrupt remapping has no big side effect. You only have to
load vfio with a special parameter so allow unsafe interrupts to do
device assignment with KVM.


	Joerg