Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757920AbcDHHom (ORCPT ); Fri, 8 Apr 2016 03:44:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49048 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757295AbcDHHol (ORCPT ); Fri, 8 Apr 2016 03:44:41 -0400 Subject: Re: [PATCH] kvm-pr: manage single-step mode To: Laurent Vivier , 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> 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: Thomas Huth Message-ID: <57076159.70504@redhat.com> Date: Fri, 8 Apr 2016 09:44:25 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.0 MIME-Version: 1.0 In-Reply-To: <5707569B.1000704@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: 3297 Lines: 96 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 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? Thomas