From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] KVM: Use thread debug register storage instead of kvm specific data Date: Tue, 01 Sep 2009 14:16:25 +0300 Message-ID: <4A9D0289.7080201@redhat.com> References: <1251798248-13164-1-git-send-email-avi@redhat.com> <4A9CFA90.50202@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , "kvm@vger.kernel.org" To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:15703 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753351AbZIALQ1 (ORCPT ); Tue, 1 Sep 2009 07:16:27 -0400 In-Reply-To: <4A9CFA90.50202@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On 09/01/2009 01:42 PM, Jan Kiszka wrote: > >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 891234b..9e3acbd 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -3627,14 +3627,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) >> >> kvm_guest_enter(); >> >> - get_debugreg(vcpu->arch.host_dr6, 6); >> - get_debugreg(vcpu->arch.host_dr7, 7); >> if (unlikely(vcpu->arch.switch_db_regs)) { >> - get_debugreg(vcpu->arch.host_db[0], 0); >> - get_debugreg(vcpu->arch.host_db[1], 1); >> - get_debugreg(vcpu->arch.host_db[2], 2); >> - get_debugreg(vcpu->arch.host_db[3], 3); >> - >> > I'm fine with this for the common case, but we should switch to the safe > pattern on test_thread_flag(TIF_DEBUG), ie. if someone debugs qemu using > hardware break/watchpoints. > IIUC, thread.debugregs should be synced with the hardware registers. The kernel itself only writes to the debug registers, so we're safe doing the same. > >> set_debugreg(0, 7); >> set_debugreg(vcpu->arch.eff_db[0], 0); >> set_debugreg(vcpu->arch.eff_db[1], 1); >> @@ -3645,15 +3638,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) >> trace_kvm_entry(vcpu->vcpu_id); >> kvm_x86_ops->run(vcpu); >> >> - if (unlikely(vcpu->arch.switch_db_regs)) { >> - set_debugreg(0, 7); >> - set_debugreg(vcpu->arch.host_db[0], 0); >> - set_debugreg(vcpu->arch.host_db[1], 1); >> - set_debugreg(vcpu->arch.host_db[2], 2); >> - set_debugreg(vcpu->arch.host_db[3], 3); >> + if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) { >> > IIRC, you must clear dr7 before loading dr0..3 to avoid spurious effects. > Yeah, I thought of it but forgot to implement it. >> + set_debugreg(current->thread.debugreg0, 0); >> + set_debugreg(current->thread.debugreg1, 1); >> + set_debugreg(current->thread.debugreg2, 2); >> + set_debugreg(current->thread.debugreg3, 3); >> + set_debugreg(current->thread.debugreg6, 6); >> + set_debugreg(current->thread.debugreg7, 7); >> } >> - set_debugreg(vcpu->arch.host_dr6, 6); >> - set_debugreg(vcpu->arch.host_dr7, 7); >> > Unless I miss something ATM, moving this into the if-clause should cause > troubles if the guest leaves dr7 armed behind. But I need to refresh my > memory on this. > The hardware will clear dr7 on exit. Updated patch to follow. -- error compiling committee.c: too many arguments to function