Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932264AbcDHG6n (ORCPT ); Fri, 8 Apr 2016 02:58:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44786 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753808AbcDHG6l (ORCPT ); Fri, 8 Apr 2016 02:58:41 -0400 Subject: Re: [PATCH] kvm-pr: manage single-step mode To: Thomas Huth , kvm-ppc@vger.kernel.org, kvm@vger.kernel.org References: <1458658428-19566-1-git-send-email-lvivier@redhat.com> <57074E45.4040204@redhat.com> Cc: Gleb Natapov , Paolo Bonzini , Alexander Graf , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, dgibson@redhat.com From: Laurent Vivier Message-ID: <5707569B.1000704@redhat.com> Date: Fri, 8 Apr 2016 08:58:35 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1 MIME-Version: 1.0 In-Reply-To: <57074E45.4040204@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2510 Lines: 76 On 08/04/2016 08:23, Thomas Huth wrote: > On 22.03.2016 15:53, Laurent Vivier wrote: >> Until now, when we connect gdb to the QEMU gdb-server, the >> single-step mode is not managed. >> >> This patch adds this, only for kvm-pr: >> >> If KVM_GUESTDBG_SINGLESTEP is set, we enable single-step trace bit in the >> MSR (MSR_SE) just before the __kvmppc_vcpu_run(), and disable it just after. >> In kvmppc_handle_exit_pr, instead of routing the interrupt to >> the guest, we return to host, with KVM_EXIT_DEBUG reason. >> >> Signed-off-by: Laurent Vivier >> --- >> arch/powerpc/kvm/book3s_pr.c | 31 +++++++++++++++++++++++++++++-- >> 1 file changed, 29 insertions(+), 2 deletions(-) >> >> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c >> index 95bceca..e6896f4 100644 >> --- a/arch/powerpc/kvm/book3s_pr.c >> +++ b/arch/powerpc/kvm/book3s_pr.c >> @@ -882,6 +882,24 @@ void kvmppc_set_fscr(struct kvm_vcpu *vcpu, u64 fscr) >> } >> #endif >> >> +static void kvmppc_setup_debug(struct kvm_vcpu *vcpu) >> +{ >> + if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) { >> + u64 msr = kvmppc_get_msr(vcpu); >> + >> + kvmppc_set_msr(vcpu, msr | MSR_SE); >> + } >> +} >> + >> +static void kvmppc_clear_debug(struct kvm_vcpu *vcpu) >> +{ >> + if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) { >> + u64 msr = kvmppc_get_msr(vcpu); >> + >> + kvmppc_set_msr(vcpu, msr & ~MSR_SE); >> + } >> +} >> + >> int kvmppc_handle_exit_pr(struct kvm_run *run, struct kvm_vcpu *vcpu, >> unsigned int exit_nr) >> { >> @@ -1208,8 +1226,13 @@ program_interrupt: >> #endif >> case BOOK3S_INTERRUPT_MACHINE_CHECK: >> case BOOK3S_INTERRUPT_TRACE: >> - kvmppc_book3s_queue_irqprio(vcpu, exit_nr); >> - r = RESUME_GUEST; >> + if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) { >> + run->exit_reason = KVM_EXIT_DEBUG; >> + r = RESUME_HOST; >> + } else { >> + kvmppc_book3s_queue_irqprio(vcpu, exit_nr); >> + r = RESUME_GUEST; >> + } > > Should the new code rather be limited to the BOOK3S_INTERRUPT_TRACE case > only? I mean, this way, you never can deliver a machine check interrupt > to the guest if singlestep debugging is enabled on the host, can you? You're right but it adds complexity and it would be only useful to single-step the single-step mode of the guest. It's hard to imagine a developer single-stepping the guest kernel while he is single-stepping a user application in the guest. It's why I have completely by-passed this case. Thanks, Laurent