With the following qemu 1.7.0 command line for a Windows 7 64-bit virtual machine, I often get "Assertion `bm->bus->dma->aiocb == ((void *)0)' failed" during certain heavy io operations such as during Windows Update or multiple file move/copy operations. qemu-system-x86_64 -machine accel=kvm -smp cores=1,threads=2,sockets=1 -cpu Penryn,+vmx,+svm -k en-us -net tap,vlan=0,ifname=<tapiface>,script=no -net nic,vlan=0,macaddr=<custommacaddr>,model=virtio -rtc base=localtime,clock=host,driftfix=slew -m 2048 -boot c -drive id=mainfs,file=disk.raw,if=ide,cache=writeback,discard=on,media=disk,format=raw -no-hpet -vga cirrus -spice port=<custom_port>,addr=127.0.0.1,password='<secret>' -name virtualmachine -serial none -parallel none -runas <restricted_user> -monitor unix:virtualmachine.monitor.sock,server,nowait -pidfile virtualmachine.pid Windows write-caching is enabled and Windows write-cache buffer flushing is disabled as well. Use flags for qemu: USE="aio alsa caps filecaps seccomp spice threads usb uuid vde vhost-net virtfs vnc xattr -accessibility -bluetooth -curl -debug -fdt -glusterfs -gtk -iscsi -jpeg -mixemu -ncurses -opengl -png -pulseaudio -python -rbd -sasl -sdl (-selinux) -smartcard -ssh -static -static-softmmu -static-user -systemtap -tci {-test} -tls -usbredir -xen -xfs" PYTHON_TARGETS="python2_7 -python2_6" QEMU_SOFTMMU_TARGETS="i386 x86_64 -alpha -arm -cris -lm32 -m68k -microblaze -microblazeel -mips -mips64 -mips64el -mipsel -moxie -or32 -ppc -ppc64 -ppcemb -s390x -sh4 -sh4eb -sparc -sparc64 -unicore32 -xtensa -xtensaeb" QEMU_USER_TARGETS="i386 x86_64 -alpha -arm -armeb -cris -m68k -microblaze -microblazeel -mips -mips64 -mips64el -mipsel -mipsn32 -mipsn32el -or32 -ppc -ppc64 -ppc64abi32 -s390x -sh4 -sh4eb -sparc -sparc32plus -sparc64 -unicore32" My emerge info: Portage 2.1.12.2 (hardened/linux/amd64, gcc-4.6.3, unavailable, 3.8.6-hardened x86_64) ================================================================= System uname: Linux-3.8.6-hardened-x86_64-Intel-R-_Core-TM-_i7-3820_CPU_@_3.60GHz-with-gentoo-2.1 KiB Mem: 65989756 total, 349520 free KiB Swap: 134213628 total, 132833080 free Timestamp of tree: Thu, 13 Feb 2014 14:15:01 +0000 ld GNU ld (GNU Binutils) 2.22 app-shells/bash: 4.2_p45 dev-java/java-config: 1.3.7, 2.1.12-r1 dev-lang/python: 2.4.4-r14, 2.5.4-r2, 2.6.8, 2.7.3-r3, 3.2.3-r2 dev-util/cmake: 2.8.10.2-r2 dev-util/pkgconfig: 0.27.1 sys-apps/baselayout: 2.1-r1 sys-apps/openrc: 0.11.8 sys-apps/sandbox: 2.6-r1 sys-devel/autoconf: 2.13::<unknown repository>, 2.68 sys-devel/automake: 1.4_p6::<unknown repository>, 1.5::<unknown repository>, 1.6.3::<unknown repository>, 1.7.9-r1::<unknown repository>, 1.8.5-r3::<unknown repository>, 1.9.6-r2::<unknown repository>, 1.10.1, 1.11.1, 1.12.6, 1.13.4 sys-devel/binutils: 2.22-r1 sys-devel/gcc: 3.4.6-r2::<unknown repository>, 4.1.2::<unknown repository>, 4.3.6-r1, 4.5.3-r2, 4.6.3 sys-devel/gcc-config: 1.7.3 sys-devel/libtool: 2.4-r1 sys-devel/make: 3.82-r3 sys-kernel/linux-headers: 3.7 (virtual/os-headers) sys-libs/glibc: 2.15-r3 Repositories: gentoo x-portage ACCEPT_KEYWORDS="amd64" ACCEPT_LICENSE="* -@EULA" CBUILD="x86_64-pc-linux-gnu" CFLAGS="-O2 -mtune=amdfam10 -fomit-frame-pointer -ftree-vectorize -fpredictive-commoning -fno-tree-vect-loop-version" CHOST="x86_64-pc-linux-gnu" CONFIG_PROTECT="/etc /usr/kde/3.5/env /usr/kde/3.5/share/config /usr/kde/3.5/shutdown /usr/share/config /usr/share/gnupg/qualified.txt /usr/share/openvpn/easy-rsa /var/bind" CONFIG_PROTECT_MASK="/etc/ca-certificates.conf /etc/env.d /etc/fonts/fonts.conf /etc/gconf /etc/gentoo-release /etc/php/apache2-php5/ext-active/ /etc/php/cgi-php5/ext-active/ /etc/php/cli-php5/ext-active/ /etc/revdep-rebuild /etc/sandbox.d /etc/terminfo" CXXFLAGS="-O2 -mtune=amdfam10 -fomit-frame-pointer -ftree-vectorize -fpredictive-commoning -fno-tree-vect-loop-version" DISTDIR="/usr/portage/distfiles" FCFLAGS="-O2 -pipe" FEATURES="assume-digests binpkg-logs distlocks ebuild-locks fixlafiles merge-sync news parallel-fetch preserve-libs protect-owned sandbox sfperms strict unknown-features-warn unmerge-logs unmerge-orphans userfetch xattr" FFLAGS="-O2 -pipe" GENTOO_MIRRORS="http://mirror.internode.on.net/pub/gentoo http://mirror.pacific.net.au/linux/Gentoo http://distfiles.gentoo.org http://www..ibiblio.org/pub/Linux/distributions/gentoo" LANG="en_AU.utf8" LDFLAGS="-Wl,-O1 -Wl,--as-needed" MAKEOPTS="-j1" PKGDIR="/usr/portage/packages" PORTAGE_CONFIGROOT="/" PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress --force --whole-file --delete --stats --human-readable --timeout=180 --exclude=/distfiles --exclude=/local --exclude=/packages" PORTAGE_TMPDIR="/var/tmp" PORTDIR="/usr/portage" PORTDIR_OVERLAY="/usr/local/portage" SYNC="rsync://mirror.internode.on.net/gentoo-portage" USE="acl acpi alsa amd64 apache2 berkdb bzip2 caps cjk cli cracklib crypt cups cxx dlloader dri fam gdbm hardened iconv ipv6 jpeg justify kdeenablefinal kdehiddenvisibility kerberos logrotate mmx mng modules multilib ncurses nls nptl openmp pam pax_kernel pcre png qt readline session sse sse2 ssl tcpd threads tiff unicode urandom vhosts xattr xcb xinerama xtpax zlib" ABI_X86="64" ALSA_CARDS="ali5451 als4000 atiixp atiixp-modem bt87x ca0106 cmipci emu10k1x ens1370 ens1371 es1938 es1968 fm801 hda-intel intel8x0 intel8x0m maestro3 trident usb-audio via82xx via82xx-modem ymfpci" APACHE2_MODULES="actions alias auth_basic auth_digest authn_anon authn_dbd authn_dbm authn_default authn_file authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache dav dav_fs dav_lock dbd deflate dir disk_cache env expires ext_filter file_cache filter headers ident imagemap include info log_config logio mem_cache mime mime_magic negotiation proxy proxy_ajp proxy_balancer proxy_connect proxy_http rewrite setenvif so speling status unique_id userdir usertrack vhost_alias cgid" CALLIGRA_FEATURES="kexi words flow plan sheets stage tables krita karbon braindump author" CAMERAS="ptp2" COLLECTD_PLUGINS="df interface irq load memory rrdtool swap syslog" ELIBC="glibc" GPSD_PROTOCOLS="ashtech aivdm earthmate evermore fv18 garmin garmintxt gpsclock itrax mtk3301 nmea ntrip navcom oceanserver oldstyle oncore rtcm104v2 rtcm104v3 sirf superstar2 timing tsip tripmate tnt ublox ubx" INPUT_DEVICES="evdev keyboard mouse" KERNEL="linux" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" LIBREOFFICE_EXTENSIONS="presenter-console presenter-minimizer" LINGUAS="en en_GB en_US en_AU" OFFICE_IMPLEMENTATION="libreoffice" PHP_TARGETS="php5-3" PYTHON_SINGLE_TARGET="python2_7" PYTHON_TARGETS="python2_7 python3_3" QEMU_SOFTMMU_TARGETS="i386 x86_64" QEMU_USER_TARGETS="i386 x86_64" RUBY_TARGETS="ruby19 ruby18" USERLAND="GNU" VIDEO_CARDS="fbdev vesa" XTABLES_ADDONS="quota2 psd pknock lscan length2 ipv4options ipset ipp2p iface geoip fuzzy condition tee tarpit sysrq steal rawnat logmark ipmark dhcpmac delude chaos account" Unset: CPPFLAGS, CTARGET, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LC_ALL, PORTAGE_BUNZIP2_COMMAND, PORTAGE_COMPRESS, PORTAGE_COMPRESS_FLAGS, PORTAGE_RSYNC_EXTRA_OPTS, USE_PYTHON
you can try 1.7.1 or 2.0.0 in the tree if they still fail, your best bet really is to send this upstream: http://wiki.qemu.org/Contribute/ReportABug
