We need to set cs->halted to 1 before calling ppc_set_compat. The reason
is that ppc_set_compat kicks up the new thread created to manage the
hotplugged KVM virtual CPU and the code drives directly to KVM_RUN
ioctl. When cs->halted is 1, the code:
int kvm_cpu_exec(CPUState *cpu)
...
if (kvm_arch_process_async_events(cpu)) {
atomic_set(&cpu->exit_request, 0);
return EXCP_HLT;
}
...
returns before it reaches KVM_RUN, giving time to the main thread to
finish its job. Otherwise we can fall in a deadlock because the KVM
thread will issue the KVM_RUN ioctl while the main thread is setting up
KVM registers. Depending on how these jobs are scheduled we'll end up
freezing QEMU.
The following output shows kvm_vcpu_ioctl sleeping because it cannot get
the mutex and never will.
PS: kvm_vcpu_ioctl was triggered kvm_set_one_reg - compat_pvr.
STATE: TASK_UNINTERRUPTIBLE|TASK_WAKEKILL
PID: 61564 TASK: c000003e981e0780 CPU: 48 COMMAND: "qemu-system-ppc"
#0 [c000003e982679a0] __schedule at c000000000b10a44
#1 [c000003e98267a60] schedule at c000000000b113a8
#2 [c000003e98267a90] schedule_preempt_disabled at c000000000b11910
#3 [c000003e98267ab0] __mutex_lock at c000000000b132ec
#4 [c000003e98267bc0] kvm_vcpu_ioctl at c00800000ea03140 [kvm]
#5 [c000003e98267d20] do_vfs_ioctl at c000000000407d30
#6 [c000003e98267dc0] ksys_ioctl at c000000000408674
#7 [c000003e98267e10] sys_ioctl at c0000000004086f8
#8 [c000003e98267e30] system_call at c00000000000b488
crash> struct -x kvm.vcpus 0xc000003da0000000
vcpus = {0xc000003db4880000, 0xc000003d52b80000, 0xc0000039e9c80000, 0xc000003d0e200000, 0xc000003d58280000, 0x0, 0x0, ...}
crash> struct -x kvm_vcpu.mutex.owner 0xc000003d58280000
mutex.owner = {
counter = 0xc000003a23a5c881 <- flag 1: waiters
},
crash> bt 0xc000003a23a5c880
PID: 61579 TASK: c000003a23a5c880 CPU: 9 COMMAND: "CPU 4/KVM"
(active)
crash> struct -x kvm_vcpu.mutex.wait_list 0xc000003d58280000
mutex.wait_list = {
next = 0xc000003e98267b10,
prev = 0xc000003e98267b10
},
crash> struct -x mutex_waiter.task 0xc000003e98267b10
task = 0xc000003e981e0780
The following command-line was used to reproduce the problem (note: gdb
and trace can change the results).
$ qemu-ppc/build/ppc64-softmmu/qemu-system-ppc64 -cpu host \
-enable-kvm -m 4096 \
-smp 4,maxcpus=8,sockets=1,cores=2,threads=4 \
-display none -nographic \
-drive file=disk1.qcow2,format=qcow2
...
(qemu) device_add host-spapr-cpu-core,core-id=4
[no interaction is possible after it, only SIGKILL to take the terminal
back]
Signed-off-by: Jose Ricardo Ziviani <joserz@linux.ibm.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
QEMU README
===========
QEMU is a generic and open source machine & userspace emulator and
virtualizer.
QEMU is capable of emulating a complete machine in software without any
need for hardware virtualization support. By using dynamic translation,
it achieves very good performance. QEMU can also integrate with the Xen
and KVM hypervisors to provide emulated hardware while allowing the
hypervisor to manage the CPU. With hypervisor support, QEMU can achieve
near native performance for CPUs. When QEMU emulates CPUs directly it is
capable of running operating systems made for one machine (e.g. an ARMv7
board) on a different machine (e.g. an x86_64 PC board).
QEMU is also capable of providing userspace API virtualization for Linux
and BSD kernel interfaces. This allows binaries compiled against one
architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a
different architecture ABI (e.g. the Linux x86_64 ABI). This does not
involve any hardware emulation, simply CPU and syscall emulation.
QEMU aims to fit into a variety of use cases. It can be invoked directly
by users wishing to have full control over its behaviour and settings.
It also aims to facilitate integration into higher level management
layers, by providing a stable command line interface and monitor API.
It is commonly invoked indirectly via the libvirt library when using
open source applications such as oVirt, OpenStack and virt-manager.
QEMU as a whole is released under the GNU General Public License,
version 2. For full licensing details, consult the LICENSE file.
Building
========
QEMU is multi-platform software intended to be buildable on all modern
Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety
of other UNIX targets. The simple steps to build QEMU are:
mkdir build
cd build
../configure
make
Additional information can also be found online via the QEMU website:
https://qemu.org/Hosts/Linux
https://qemu.org/Hosts/Mac
https://qemu.org/Hosts/W32
Submitting patches
==================
The QEMU source code is maintained under the GIT version control system.
git clone git://git.qemu.org/qemu.git
When submitting patches, one common approach is to use 'git
format-patch' and/or 'git send-email' to format & send the mail to the
qemu-devel@nongnu.org mailing list. All patches submitted must contain
a 'Signed-off-by' line from the author. Patches should follow the
guidelines set out in the HACKING and CODING_STYLE files.
Additional information on submitting patches can be found online via
the QEMU website
https://qemu.org/Contribute/SubmitAPatch
https://qemu.org/Contribute/TrivialPatches
The QEMU website is also maintained under source control.
git clone git://git.qemu.org/qemu-web.git
https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/
A 'git-publish' utility was created to make above process less
cumbersome, and is highly recommended for making regular contributions,
or even just for sending consecutive patch series revisions. It also
requires a working 'git send-email' setup, and by default doesn't
automate everything, so you may want to go through the above steps
manually for once.
For installation instructions, please go to
https://github.com/stefanha/git-publish
The workflow with 'git-publish' is:
$ git checkout master -b my-feature
$ # work on new commits, add your 'Signed-off-by' lines to each
$ git publish
Your patch series will be sent and tagged as my-feature-v1 if you need to refer
back to it in the future.
Sending v2:
$ git checkout my-feature # same topic branch
$ # making changes to the commits (using 'git rebase', for example)
$ git publish
Your patch series will be sent with 'v2' tag in the subject and the git tip
will be tagged as my-feature-v2.
Bug reporting
=============
The QEMU project uses Launchpad as its primary upstream bug tracker. Bugs
found when running code built from QEMU git or upstream released sources
should be reported via:
https://bugs.launchpad.net/qemu/
If using QEMU via an operating system vendor pre-built binary package, it
is preferable to report bugs to the vendor's own bug tracker first. If
the bug is also known to affect latest upstream code, it can also be
reported via launchpad.
For additional information on bug reporting consult:
https://qemu.org/Contribute/ReportABug
Contact
=======
The QEMU community can be contacted in a number of ways, with the two
main methods being email and IRC
- qemu-devel@nongnu.org
https://lists.nongnu.org/mailman/listinfo/qemu-devel
- #qemu on irc.oftc.net
Information on additional methods of contacting the community can be
found online via the QEMU website:
https://qemu.org/Contribute/StartHere
-- End
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