This bug is triggered for my Windows XP guest, but not for my linux guests.
The gdb result shows that a "vga.vram" memoryregion is added twice.
------------libvirt log -------
2011-10-25 16:18:58.117: starting up
LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin QEMU_AUDIO_DRV=none /home/laijs/bin/qemu.sh -S -M pc-0.13 -enable-kvm -m 256 -smp 1,sockets=1,cores=1,threads=1 -name Windows -uuid 3b0f4f29-1ca1-c199-a080-3ccac8f745a9 -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/Windows.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=localtime -no-shutdown -drive file=/home/laijs/Windows/windows.img,if=none,id=drive-ide0-0-0,format=qcow2,cache=none -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 -drive file=/home/laijs/OFFICE2003_STD_EN.ISO,if=none,media=cdrom,id=drive-ide0-1-0,readonly=on,format=raw -device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -netdev tap,fd=17,id=hostnet0 -device pcnet,netdev=hostnet0,id=net0,mac=52:54:00:a5:d2:ea,bus=pci.0,multifunction=on,addr=0x3.0x0 -usb -vnc 127.0.0.1:0 -vga std -device virtio-balloon-pci,id=balloon0,bus=pci.0,multifunction=on,addr=0
x5.0x0
Domain id=45 is tainted: high-privileges
qemu-system-x86_64: /home/laijs/work/qemu-kvm/memory.c:1083: memory_region_add_subregion_common: Assertion `!subregion->parent' failed.
2011-10-25 16:18:58.380: shutting down
-------------git bisect result
b195043003d90ea4027ea01cc7a6c974ac915108 is the first bad commit
commit b195043003d90ea4027ea01cc7a6c974ac915108
Author: Avi Kivity <avi@xxxxxxxxxx>
Date: Mon Aug 8 16:08:57 2011 +0300
vga: convert vga and its derivatives to the memory API
Convert all vga memory to the memory API. Note we need to fall back to
get_system_memory(), since the various buses don't pass the vga window
as a memory region.
We no longer need to sync the dirty bitmap of the cirrus mapped memory
banks, since the memory API takes care of that for us.
[jan: fix vga-pci logging]
Reviewed-by: Richard Henderson <rth@xxxxxxxxxxx>
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>
:040000 040000 e8faf8e539a4ec814ef212ce97040046363a67f3 917701ddf6a42f49204a5b2adfa9654c03c0d6f6 M hw
-----------------------gdb result(b19504300)--------
(gdb) bt
#0 0x000000000042995a in memory_region_add_subregion_common (mr=0x2a799a0, offset=4026531840,
subregion=0x2d17250) at /home/laijs/work/qemu-kvm/memory.c:1083
#1 0x0000000000590408 in pci_update_mappings (d=0x2d16f40)
at /home/laijs/work/qemu-kvm/hw/pci.c:1123
#2 0x0000000000590846 in pci_default_write_config (d=0x2d16f40, addr=4,
val=<value optimized out>, l=<value optimized out>) at /home/laijs/work/qemu-kvm/hw/pci.c:1173
#3 0x0000000000427616 in kvm_handle_io (env=0x2bdf500) at /home/laijs/work/qemu-kvm/kvm-all.c:837
#4 kvm_cpu_exec (env=0x2bdf500) at /home/laijs/work/qemu-kvm/kvm-all.c:976
#5 0x000000000040c308 in cpu_exec_all () at /home/laijs/work/qemu-kvm/cpus.c:1102
#6 0x0000000000587281 in main_loop (argc=<value optimized out>, argv=<value optimized out>,
envp=<value optimized out>) at /home/laijs/work/qemu-kvm/vl.c:1392
#7 main (argc=<value optimized out>, argv=<value optimized out>, envp=<value optimized out>)
at /home/laijs/work/qemu-kvm/vl.c:3356
(gdb) p mr->name
$1 = 0x2a79a70 "system"
(gdb) p subregion->name
$2 = 0x2c02960 "vga.vram"
(gdb) p *subregion
$3 = {ops = 0x0, opaque = 0x0, parent = 0x2a799a0, size = 8388608, addr = 3758096384, offset = 0,
backend_registered = true, ram_addr = 268697600, iorange = {ops = 0x0, base = 0, len = 0},
terminates = true, alias = 0x0, alias_offset = 0, priority = 1, may_overlap = true, subregions =
{tqh_first = 0x0, tqh_last = 0x2d172c8}, subregions_link = {tqe_next = 0x2b7d610, tqe_prev =
0x2b7d788}, coalesced = {tqh_first = 0x0, tqh_last = 0x2d172e8}, name = 0x2c02960 "vga.vram",
dirty_log_mask = 1 '\001', ioeventfd_nb = 0, ioeventfds = 0x0}
(gdb) p subregion->parent
$4 = (MemoryRegion *) 0x2a799a0
(gdb) p *subregion->parent
$5 = {ops = 0x0, opaque = 0x0, parent = 0x0, size = 9223372036854775807, addr = 0, offset = 0,
backend_registered = false, ram_addr = 0, iorange = {ops = 0x0, base = 0, len = 0}, terminates =
false, alias = 0x0, alias_offset = 0, priority = 0, may_overlap = false, subregions = {
tqh_first = 0x2acc120, tqh_last = 0x2b4d168}, subregions_link = {tqe_next = 0x0, tqe_prev =
0x0}, coalesced = {tqh_first = 0x0, tqh_last = 0x2a79a38}, name = 0x2a79a70 "system",
dirty_log_mask = 0 '\000', ioeventfd_nb = 0, ioeventfds = 0x0}
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