On Wed, Mar 08, 2017 at 11:41:32AM +1100, Paul Mackerras wrote: > commit 88b02cf97bb7e742db3e31671d54177e3e19fd89 upstream. > > POWER8 has one virtual timebase (VTB) register per subcore, not one > per CPU thread. The HV KVM code currently treats VTB as a per-thread > register, which can lead to spurious soft lockup messages from guests > which use the VTB as the time source for the soft lockup detector. > (CPUs before POWER8 did not have the VTB register.) > > For HV KVM, this fixes the problem by making only the primary thread > in each virtual core save and restore the VTB value. With this, > the VTB state becomes part of the kvmppc_vcore structure. This > also means that "piggybacking" of multiple virtual cores onto one > subcore is not possible on POWER8, because then the virtual cores > would share a single VTB register. > > PR KVM emulates a VTB register, which is per-vcpu because PR KVM > has no notion of CPU threads or SMT. For PR KVM we move the VTB > state into the kvmppc_vcpu_book3s struct. > > Cc: stable@xxxxxxxxxxxxxxx # v3.14+ > Reported-by: Thomas Huth <thuth@xxxxxxxxxx> > Tested-by: Thomas Huth <thuth@xxxxxxxxxx> > Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx> > --- > This is intended for the 4.8 stable tree. 4.8 is long gone and not being maintained anymore, so there's not much we can do with this, sorry. Was there a specific distro that you were concerned about not picking this up? thanks, greg k-h