Re: [gentoo-user] Re: Issues with AMD_IOMMU

[Adam Carter]

On Wed, May 17, 2017 at 12:25 AM, Corbin Bird <corbinbird@×××××××.net>
wrote:

> On 05/16/2017 01:34 AM, Adam Carter wrote:
> > Answer #1 :
> >
> >
> >     Asrock, Extreme6, 990FX, UEFI, AMD FX-9590
> >     Gigabyte, GA-MA790FX-UD5P, 790FX, BIOS, AMD PhenomII x4 980
> >
> >
> > Hi Corbin,
> >
> > I noticed i didnt have x2apic enabled on my 990FX / FX-8350 system, so
> > i've rebuilt/rebooted etc, but;
> >
> > # zgrep X2APIC /proc/config.gz
> > CONFIG_X86_X2APIC=y
> > # dmesg | grep -i x2apic
> > #
> >
> > On my skylake box
> > # dmesg | grep -i x2apic
> > [    0.044148] DMAR-IR: Queued invalidation will be enabled to support
> > x2apic and Intr-remapping.
> > [    0.045802] DMAR-IR: Enabled IRQ remapping in x2apic mode
> > [    0.045908] x2apic enabled
> > [    0.046011] Switched APIC routing to cluster x2apic.
> >
> > What x2apic messages do you get on your 990FX / FX-9590 system?
>
>
> Interesting kernel parameter for you to try :
> ( from '/usr/src/linux/Documentation/kernel-parameters.txt' )
>
> x2apic_phys     [X86-64,APIC] Use x2apic physical mode instead of
>                         default x2apic cluster mode on platforms
>                         supporting x2apic.
>
> With that switch I have not been getting any output in 'dmesg' about
> this at all.
>

I tried adding x2apic_phys, but dmesg output did not change.

From wikip;
"In 2012, AMD announced their *Advanced Virtual Interrupt Controller* (
*AVIC*) targeting interrupt overhead reduction in virtualization
environments.[33]
<https://en.wikipedia.org/wiki/X86_virtualization#cite_note-33> This
technology has materialize in hardware and (as announced) does not support
x2APIC <https://en.wikipedia.org/wiki/X2APIC>.[34]
<https://en.wikipedia.org/wiki/X86_virtualization#cite_note-34> In 2016,
AVIC is available on the AMD family 15h models 6Xh (Carrizo) processors and
newer.[35]" <https://en.wikipedia.org/wiki/X86_virtualization#cite_note-35>

So;
FX-8350 processors (bulldozer gen2) dont have AVIC
Carrizo processors (bulldozer gen4), have AVIC, but AVIC doesnt support
x2apic
seems reasonable to conclude that there's no x2apic on bulldozer gen2, and
that's why there's nothing in dmesg about it.


> Question :
> Do you have this enabled in your kernel ...
> >   [ ]   Support for Intel IOMMU using DMA Remapping Devices
>

On the Skylake box, yes, FX box, no.