From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 1/6] KVM: Check for pending events before attempting injection Date: Wed, 28 Jul 2010 19:53:32 +0300 Message-ID: <4C50608C.7020207@redhat.com> References: <1280236780-5847-1-git-send-email-avi@redhat.com> <1280236780-5847-2-git-send-email-avi@redhat.com> <20100728162119.GA25224@amt.cnet> <4C505B47.5090405@redhat.com> <20100728163713.GA26653@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Marcelo Tosatti Return-path: Received: from mx1.redhat.com ([209.132.183.28]:50474 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752771Ab0G1Qxg (ORCPT ); Wed, 28 Jul 2010 12:53:36 -0400 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o6SGrZRB021144 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 28 Jul 2010 12:53:35 -0400 In-Reply-To: <20100728163713.GA26653@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On 07/28/2010 07:37 PM, Marcelo Tosatti wrote: > On Wed, Jul 28, 2010 at 07:31:03PM +0300, Avi Kivity wrote: >> On 07/28/2010 07:21 PM, Marcelo Tosatti wrote: >>> On Tue, Jul 27, 2010 at 04:19:35PM +0300, Avi Kivity wrote: >>>> Instead of blindly attempting to inject an event before each guest entry, >>>> check for a possible event first in vcpu->requests. Sites that can trigger >>>> event injection are modified to set KVM_REQ_EVENT: >>>> >>>> - interrupt, nmi window opening >>>> - ppr updates >>>> - i8259 output changes >>>> - local apic irr changes >>>> - rflags updates >>>> - gif flag set >>>> - event set on exit >>>> >>>> This improves non-injecting entry performance, and sets the stage for >>>> non-atomic injection. >>>> >>>> Signed-off-by: Avi Kivity >>>> --- >>>> arch/x86/kvm/i8259.c | 1 + >>>> arch/x86/kvm/lapic.c | 12 ++++++++++-- >>>> arch/x86/kvm/svm.c | 8 +++++++- >>>> arch/x86/kvm/vmx.c | 6 ++++++ >>>> arch/x86/kvm/x86.c | 35 ++++++++++++++++++++++++++--------- >>>> include/linux/kvm_host.h | 1 + >>>> 6 files changed, 51 insertions(+), 12 deletions(-) >>>> >>>> @@ -4731,17 +4737,19 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) >>>> goto out; >>>> } >>>> >>>> - inject_pending_event(vcpu); >>>> + if (kvm_check_request(KVM_REQ_EVENT, vcpu)) { >>>> + inject_pending_event(vcpu); >>>> >>>> - /* enable NMI/IRQ window open exits if needed */ >>>> - if (vcpu->arch.nmi_pending) >>>> - kvm_x86_ops->enable_nmi_window(vcpu); >>>> - else if (kvm_cpu_has_interrupt(vcpu) || req_int_win) >>>> - kvm_x86_ops->enable_irq_window(vcpu); >>>> + /* enable NMI/IRQ window open exits if needed */ >>>> + if (vcpu->arch.nmi_pending) >>>> + kvm_x86_ops->enable_nmi_window(vcpu); >>>> + else if (kvm_cpu_has_interrupt(vcpu) || req_int_win) >>>> + kvm_x86_ops->enable_irq_window(vcpu); >>> Problem is it might not be possible to inject the event signalled by >>> KVM_REQ_EVENT, say an interrupt from an irqchip, if there is an event >>> that needs reinjection (or an exception). >> That can happen event now, no? A pending exception, interrupt comes >> along, injection picks up the exception but leaves the interrupt. >> >> Now the situation can be more complicated: >> >> - pending exception >> - injection >> - interrupt, sets KVM_REQ_EVENT >> - notices KVM_REQ_EVENT >> - drops KVM_REQ_EVENT, cancels exception (made pending again) >> - goes back >> - injection (injects exception again, interrupt is pending) >> >> as far as I can tell, this is all fine. > But you cleared KVM_REQ_EVENT. Which means you're not going to inject > the pending interrupt on the next entry. Doh. So we need to set KVM_REQ_EVENT again, after the final check for vcpu->requests, to make sure we redo injection again. So we can make inject_pending_event() return true if there's more in the queue, and if it did, re-raise KVM_REQ_EVENT just before entry? -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.