Re: IOMMU and AMD 890fx

[Andre Przywara <andre.przywara@amd.com>]

Hi,

Jörg is correct, thanks for picking this up. Some additions inline.
Joerg Roedel wrote:
> Hello Jens,
> 
> On Thu, Jun 03, 2010 at 12:51:23PM +0200, Jens Krehbiel-Gräther wrote:
>> I got this answer from asrock support:
>>
>> <answer>
>> So, I get more/final answer from Taiwan department:
>>
>> For H/W part:
>> >From chipset spec, RD890(890FX) did support IOMMU.
>> But IOMMU also need CPU to support.
> 
> Thats wrong. The IOMMU is a feature of the chipset northbridge and does
> not need additional cpu support.
> 
>> Till now, AMD has no plan to support
>> IOMMU on desktop CPU (AM3 socket).
> 
> There are AM3 boards out there with server a chipset that have it
> enabled. Its no question of a socket.
That would be the Tyan S8005, although the official CPU support list 
only lists Opteron parts (those in AM3 socket: Suzuka and Budapest)
> 
>> It only support with server CPU.
> 
> Also wrong. I have seen systems with desktop cpus that have IOMMU
> enabled (Phenom X4 and Phenom X6).
> 
>> For BIOS part:
> 
>> AMD has removed IOMMU related registers.
> 
> Hard to believe. I have found people in the net who say that the ASUS
> Crosshair IV mobo has IOMMU support in the BIOS. So if they can enable
> it, asrock can do that too. Its just the BIOS which has to enable it

If you want to check this yourself:
For out-of-the-box support there needs to be an ACPI table called IVRS 
setup by the BIOS, you can spot this in xm dmesg (or in dmesg on native 
Linux):
(XEN) ACPI: IVRS C7E7ACC8, 00E0 (r1  AMD     RD890S  6040000 AMD         0)
On a native Linux you can also find the table in /sys/firmware/acpi/tables
If the table is present, recent Xen versions (as well as Linux and KVM) 
should automatically enable and use the IOMMU.

If the ACPI table is missing, you can try to look for the corresponding 
PCI device: it should have a vendor/device-id of 1002:5a23, lspci lists 
it as:
00:00.2 Generic system peripheral [0806]: ATI Technologies Inc Device 5a23
If anyone has a board with the PCI device but a missing ACPI table, 
please tell us.

We are already trying to improve the situation, you could help us by 
reporting the IOMMU support status on 890FX boards. Simply check for the 
ACPI table:
# xm dmesg | grep IVRS    or
$ ls /sys/firmware/acpi/tables/IVRS
and by checking for the PCI device:
$ /sbin/lspci -d 1002:5a23


Hope that helps.

Regards,
Andre.


-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448 3567 12
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