Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757967AbcDHIDW (ORCPT ); Fri, 8 Apr 2016 04:03:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51182 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757908AbcDHIDQ (ORCPT ); Fri, 8 Apr 2016 04:03:16 -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> <5707569B.1000704@redhat.com> <57076159.70504@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: <570765BD.20908@redhat.com> Date: Fri, 8 Apr 2016 10:03:09 +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: <57076159.70504@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: 3543 Lines: 106 On 08/04/2016 09:44, Thomas Huth wrote: > On 08.04.2016 08:58, Laurent Vivier wrote: >> >> >> 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. > > Hmm, not sure whether you've got me right ;-) I rather meant: What Yes, I've missed what you mean. :( Thank you to try again :) > happens when a machine check is supposed to happen in the guest while > single stepping is enabled at the host level? IMHO it would be better to > shape the code like this: > > case BOOK3S_INTERRUPT_MACHINE_CHECK: > kvmppc_book3s_queue_irqprio(vcpu, exit_nr); > r = RESUME_GUEST; > break; > case BOOK3S_INTERRUPT_TRACE: > 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; > } > > That means, split the two cases, to keep the old behavior for the > MACHINE_CHECK case. That's also not too much of additional complexity, > is it? Yes, you're right. Thanks, Laurent