From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: x86: fix missed hardware breakpoints Date: Fri, 26 Feb 2016 12:40:33 +0100 Message-ID: <56D039B1.2030309@redhat.com> References: <1455879402-23009-1-git-send-email-pbonzini@redhat.com> <56D02C01.2040400@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: oleg@redhat.com, namit@cs.technion.ac.il, avagin@gmail.com, stable@vger.kernel.org To: Xiao Guangrong , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <56D02C01.2040400@linux.intel.com> Sender: stable-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 26/02/2016 11:42, Xiao Guangrong wrote: >> >> + vcpu->arch.switch_db_regs |= KVM_DEBUGREG_RELOAD; > > Er, i do not understand how it works. The BP is enabled in this test case so > the debug registers are always reloaded before entering guest as > KVM_DEBUGREG_BP_ENABLED bit is always set on switch_db_regs. What did i > miss? > > Another impact of this fix is when vcpu is rescheduled we need to always > reload debug registers even if guest does not enable it, it is really needed? Hi, I have looked further at the bug and the issue is that the lazy debug register optimization doesn't call kvm_update_dr7 and thus does not set KVM_DEBUGREG_BP_ENABLED. I will post a better patch shortly. However, I still think this one is simpler to have in stable kernel releases, because it doesn't have any dependencies. Paolo