On Fri, Jul 08, 2016 at 05:47:01PM +0200, Greg Kurz wrote: > On Fri, 08 Jul 2016 15:12:07 +0200 > Greg Kurz <gr...@kaod.org> wrote: > > > If the host has 8 threads/core and the guest is started with: > > > > -smp cores=1,threads=4,maxcpus=12 > > > > It is possible to crash QEMU by doing: > > > > (qemu) device_add host-spapr-cpu-core,core-id=16,id=foo > > (qemu) device_del foo > > Segmentation fault > > > > This is caused because spapr_core_unplug() assumes cpu_dt_id == core_id. > > Even if it happens to be the case when the host and guest have the same > > number of threads per core, it is conceptually wrong and we may pass a > > bogus id to spapr_dr_connector_by_id() and spapr_core_release() crashes. > > > > Let's use cc->core_id, which is the id that was used to create th DR > > connector. > > My bad, I got excited and pointed out the wrong culprit... it is cpu_index > again of course ! Please find an updated explanation to be put in the > changelog after "Segmentation fault": > > ======================================================================== > This happens because spapr_core_unplug() assumes cpu_dt_id == core_id. > As long as cpu_dt_id is derived from the non-table cpu_index, this is > only true when you plug cores with contiguous ids. > > It is safer to be consistent: the DR connector was created with an > index that is immediately written to cc->core_id, and spapr_core_plug() > also relies on cc->core_id. > > Let's use it also in spapr_core_unplug(). > ======================================================================== > > > > > Signed-off-by: Greg Kurz <gr...@kaod.org>
Reviewed-by: Bharata B Rao <bhar...@linux.vnet.ibm.com> This prevents the crash, but unplug still fails and that will be fixed only by having your patchset where device tree id is derived from core index. Regards, Bharata.