PCI-DMA: Out of IOMMU space on x86-64 (Athlon64x2), with solution

[Michael Monnerie <m.monnerie@zmi.at>]

Hello, I use SUSE 10.0 with all updates and actual kernel 2.6.13-15.8 as 
provided from SUSE (just self compiled to optimize for Athlon64, SMP, 
and HZ=100), with an Asus A8N-E motherboard, and an Athlon64x2 CPU. 
This host is used with VMware GSX server running 6 Linux client and one 
Windows client host. There's a SW-RAID1 using 2 SATA HDs.

When we wanted to install a new client, and inserted a DVD into the PC, 
it behaved like on drugs, showing the following output 
in /var/log/warn:

Feb 28 15:19:30 baum kernel: rtc: lost some interrupts at 256Hz.
Feb 28 15:19:47 baum kernel: rtc: lost some interrupts at 256Hz.
Feb 28 15:20:26 baum kernel: rtc: lost some interrupts at 256Hz.
Feb 28 15:20:45 baum kernel: PCI-DMA: Out of IOMMU space for 225280 
bytes at device 0000:00:08.0
Feb 28 15:20:45 baum kernel: end_request: I/O error, dev sda, sector 
12248446
Feb 28 15:20:45 baum kernel:    Operation continuing on 1 devices
Feb 28 15:20:45 baum kernel: PCI-DMA: Out of IOMMU space for 221184 
bytes at device 0000:00:08.0
Feb 28 15:20:45 baum kernel: end_request: I/O error, dev sdb, sector 
12248454
Feb 28 15:20:45 baum kernel: printk: 118 messages suppressed.
Feb 28 15:20:45 baum kernel: Buffer I/O error on device md0, logical 
block 1004928
Feb 28 15:20:45 baum kernel: lost page write due to I/O error on md0
Feb 28 15:20:45 baum kernel: Buffer I/O error on device md0, logical 
block 1004929
Feb 28 15:20:45 baum kernel: lost page write due to I/O error on md0

After that, the SW RAID stopped it's work, some VMware clients crashed 
and so on. Not a good situation.

I found this in dmesg:
CPU 0: aperture @ b6c6000000 size 32 MB
Aperture from northbridge cpu 0 too small (32 MB)
No AGP bridge found
Your BIOS doesn't leave a aperture memory hole
Please enable the IOMMU option in the BIOS setup
This costs you 64 MB of RAM
Mapping aperture over 65536 KB of RAM @ 8000000
PCI-DMA: Disabling AGP.
PCI-DMA: aperture base @ 8000000 size 65536 KB
PCI-DMA: Reserving 64MB of IOMMU area in the AGP aperture

The problem is, it's an ASUS A8N-E, and doesn't have AGP but PCI-Express 
- and therefore no more BIOS setting for the AGP aperture size.

The kernel set that IOMMU to 64MB, but it still seems to small. There's 
a kernel boot option "iommu=...", but using "iommu=off" lead to a 
frozen system during boot, and "iommu=128M" didn't boot at all.

I found a message from Andi Kleen of SUSE suggesting using 
"iommu=memaper=3", and that helped - at least until now. I just wanted 
to say thank you for that, and document this fact here for others 
possibly running into the same problem.

Output from the kernel source script "sh scripts/ver_linux":

Linux baum 2.6.13-15.8-ZMI #1 SMP Tue Feb 28 16:07:49 CET 2006 x86_64 
x86_64 x86_64 GNU/Linux

Gnu C                  4.0.2
Gnu make               3.80
binutils               2.16.91.0.2
util-linux             2.12q
mount                  2.12q
module-init-tools      3.2-pre8
e2fsprogs              1.38
jfsutils               1.1.8
reiserfsprogs          3.6.18
reiser4progs           line
xfsprogs               2.6.36
Linux C Library        2.3.5
Dynamic linker (ldd)   2.3.5
Linux C++ Library      6.0.6
Procps                 3.2.5
Net-tools              1.60
Kbd                    1.12
Sh-utils               5.3.0
udev                   068
Modules Loaded         vmnet vmmon joydev af_packet iptable_filter 
ip_tables button battery ac ipv6 ide_cd cdrom sundance mii shpchp 
pci_hotplug generic ehci_hcd i2c_nforce2 ohci_hcd usbcore i2c_core 
dm_mod reiserfs raid1 fan thermal processor sg sata_nv libata amd74xx 
sd_mod scsi_mod ide_disk ide_core
-- 
// Michael Monnerie, Ing.BSc  ---   it-management Michael Monnerie
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