From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758883AbcIMQ0U (ORCPT ); Tue, 13 Sep 2016 12:26:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35718 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754811AbcIMQ0R (ORCPT ); Tue, 13 Sep 2016 12:26:17 -0400 Subject: Re: KVM patches applied in weird order in -stable To: Greg KH , Matt Fleming References: <20160913145100.GK3872@codeblueprint.co.uk> <20160913145809.GA28002@kroah.com> Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org From: Paolo Bonzini Message-ID: <1b809ad3-2fee-b67d-fcbb-fb35e8fa7f30@redhat.com> Date: Tue, 13 Sep 2016 18:26:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20160913145809.GA28002@kroah.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Tue, 13 Sep 2016 16:26:17 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/09/2016 16:58, Greg KH wrote: > [adding stable@ as this is a stable issue, not a 'normal' issue] > > On Tue, Sep 13, 2016 at 03:51:00PM +0100, Matt Fleming wrote: >> Folks, >> >> While hunting down a performance issue involving KVM I was surprised >> to see "native_set_debugreg()" as the first entry in `perf top`. >> >> Digging deeper, it looks as though the following patches were applied >> in the wrong order in -stable. This is the order as they appear in >> Linus' tree, >> >> [0] commit 4e422bdd2f84 ("KVM: x86: fix missed hardware breakpoints") >> [1] commit 172b2386ed16 ("KVM: x86: fix missed hardware breakpoints") >> [2] commit 70e4da7a8ff6 ("KVM: x86: fix root cause for missed hardware breakpoints") >> >> but this is the order for linux-4.4.y >> >> [1] commit fc90441e728a ("KVM: x86: fix missed hardware breakpoints") >> [2] commit 25e8618619a5 ("KVM: x86: fix root cause for missed hardware breakpoints") >> [0] commit 0f6e5e26e68f ("KVM: x86: fix missed hardware breakpoints") >> >> The upshot is that KVM_DEBUGREG_RELOAD is always set when returning >> from kvm_arch_vcpu_load() in stable, but not in Linus' tree. > > How would applying these in a different order cause breakage? [2] is reverting [0]+[1]. Stable is not due to the different order. > And if this is a problem, can you please send me a patch to fix it up? Yup, on the way. Paolo