From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:47758 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751755AbdCHK0M (ORCPT ); Wed, 8 Mar 2017 05:26:12 -0500 Date: Wed, 8 Mar 2017 06:01:58 +0100 From: Greg KH To: Paul Mackerras Cc: stable@vger.kernel.org Subject: Re: [PATCH stable v4.8] KVM: PPC: Book3S: Treat VTB as a per-subcore register, not per-thread Message-ID: <20170308050158.GA3769@kroah.com> References: <20170308004132.GC14927@fergus.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170308004132.GC14927@fergus.ozlabs.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: 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@vger.kernel.org # v3.14+ > Reported-by: Thomas Huth > Tested-by: Thomas Huth > Signed-off-by: Paul Mackerras > --- > 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