kvm-88: KVM_APIC_READ: read reserved register b0

[Christoph Lechner <cl0059@l-mx.de>]

Hi all,

running kvm-88 on a 2.6.26-1-amd64 kernel (stock Debian 5.0 kernel), I
get the syslog on the host system flooded with the message:

Aug 28 11:49:40 reactor kernel: [124035.611782] KVM_APIC_READ: read
reserved register b0

The guest is running Debian 5.0 as well. Kernel 2.6.26-2-486. qemu is
started with the command line:
/opt/kvm-88/bin/qemu-system-x86_64 -hda web-int.img -m 512 -net
nic,vlan=0,macaddr=52:54:12:34:02:01 -net tap,vlan=0 -k de -vnc :4


The message is always the same, only the timestamp differs. The log msg
is generated quite often, at least 10000 times per minute. The guest
system has 100% CPU usage, so has the qemu process on the host. I was
doing a search engine crawler run -- lots of network I/O -- , when the
log was filled. See the impressive growth rate of the syslog (crawler
running)

reactor:/virt# ls -l /var/log/syslog; sleep 60; ls -l /var/log/syslog
-rw-r----- 1 root adm 17765119 2009-08-28 11:47 /var/log/syslog
-rw-r----- 1 root adm 19124492 2009-08-28 11:48 /var/log/syslog
(at least 99.9% of the new log entries are of the same kind as the one
above ...)


I seems to me that the message is related to network I/O because when I
run a netpipe-tcp TCP performance benchmark between the guest and some
real machine on the network the growth rate is even higher:
reactor:/virt# ls -l /var/log/syslog; sleep 60; ls -l /var/log/syslog
-rw-r----- 1 root adm 32404400 2009-08-28 11:59 /var/log/syslog
-rw-r----- 1 root adm 73271420 2009-08-28 12:00 /var/log/syslog
(throughput max: 240 MBit/s)


When the guest system is idle (only shell prompt), the syslog growth
rate is some magnitudes smaller:
reactor:/virt# ls -l /var/log/syslog; sleep 60; ls -l /var/log/syslog
-rw-r----- 1 root adm 29649924 2009-08-28 11:56 /var/log/syslog
-rw-r----- 1 root adm 29708722 2009-08-28 11:57 /var/log/syslog

How can I fix it?

CU
- cl

reactor:/virt# cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 16
model           : 4
model name      : AMD Phenom(tm) II X4 920 Processor
stepping        : 2
cpu MHz         : 2807.120
cache size      : 512 KB
physical id     : 0
siblings        : 4
core id         : 0
cpu cores       : 4
apicid          : 0
initial apicid  : 0
fpu             : yes
fpu_exception   : yes
cpuid level     : 5
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmovpat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext
fxsr_opt pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc rep_good pni
monitor cx16 popcnt lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a
misalignsse 3dnowprefetch osvw ibs skinit wdt
bogomips        : 5618.34
TLB size        : 1024 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 48 bits physical, 48 bits virtual
power management: ts ttp tm stc 100mhzsteps hwpstate

(the host system has a quad-core CPU)