SWIOTLB allocation failed

[Lukas Hejtmanek <xhejtman@ics.muni.cz>]

Hello,

I'm using Xen 3.1 with kernel 2.6.18. If I use swiotlb=force option to boot
domU, I got the following message:
xm create -c skirit60-1
Using config file "/etc/xen/skirit60-1".
Started domain skirit60-1
                         Bootdata ok (command line is root=/dev/sda1 ro
ip=147.251.11.44:1.2.3.4:147.251.11.1:255.255.255.128:skirit60-1:eth0:off
magrathea=eth1:10.0.0.1:10.0.0.101: swiotlb=force)
Linux version 2.6.18-xen31-smp (root@skirit60) (gcc version 4.0.2 20050901
(prerelease) (SUSE Linux)) #19 SMP Tue Jul 10 01:06:20 CEST 2007
BIOS-provided physical RAM map:
 Xen: 0000000000000000 - 000000009cc00000 (usable)
No mptable found.
Built 1 zonelists.  Total pages: 642048
Kernel command line: root=/dev/sda1 ro
ip=147.251.11.44:1.2.3.4:147.251.11.1:255.255.255.128:skirit60-1:eth0:off
magrathea=eth1:10.0.0.1:10.0.0.101: swiotlb=force
Initializing CPU#0
PID hash table entries: 4096 (order: 12, 32768 bytes)
Xen reported: 2992.500 MHz processor.
Console: colour dummy device 80x25
Dentry cache hash table entries: 524288 (order: 10, 4194304 bytes)
Inode-cache hash table entries: 262144 (order: 9, 2097152 bytes)
Kernel panic - not syncing: No suitable physical memory available for SWIOTLB
buffer!
Use dom0_mem Xen boot parameter to reserve
some DMA memory (e.g., dom0_mem=-128M).


is there something I could do to improve domU? Dom0 has only 256MB RAM, system
has 4GB RAM total. (DomU is assigned 2.5GB RAM.)

-- 
Lukáš Hejtmánek