From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH 2/3] KVM: VMX: Short circuit STI; HLT while an interrupt is pending Date: Tue, 15 Feb 2011 18:36:55 -0200 Message-ID: <20110215203654.GA16010@amt.cnet> References: <1297694537-9268-1-git-send-email-avi@redhat.com> <1297694537-9268-3-git-send-email-avi@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:47331 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753140Ab1BOUhU (ORCPT ); Tue, 15 Feb 2011 15:37:20 -0500 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 (8.14.4/8.14.4) with ESMTP id p1FKbKnJ019805 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 15 Feb 2011 15:37:20 -0500 Content-Disposition: inline In-Reply-To: <1297694537-9268-3-git-send-email-avi@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Mon, Feb 14, 2011 at 04:42:16PM +0200, Avi Kivity wrote: > Short-circuit an STI; HLT sequence while an interrupt is pending: > instead of halting, re-entering the guest, and exiting immediately > on an interrupt window exit, go directly to the last step. > > Saves a vmexit on workloads where interrupts are received synchronously; > an example is a disk backed by the host page cache where there is no > latency (from the guest's point of view) between the request and fulfilment. > > Signed-off-by: Avi Kivity > --- > arch/x86/kvm/vmx.c | 9 +++++++++ > 1 files changed, 9 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index ee1cd1a..541da0e 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -3437,6 +3437,15 @@ static int handle_interrupt_window(struct kvm_vcpu *vcpu) > static int handle_halt(struct kvm_vcpu *vcpu) > { > skip_emulated_instruction(vcpu); > + /* > + * Short-circuit an STI; HLT sequence while an interrupt is pending: > + * instead of halting, re-entering the guest, and exiting immediately > + * on an interrupt window exit, go directly to the last step. > + */ > + if ((to_vmx(vcpu)->cpu_based_vm_exec_control > + & CPU_BASED_VIRTUAL_INTR_PENDING) > + && (kvm_get_rflags(vcpu) & X86_EFLAGS_IF)) > + return handle_interrupt_window(vcpu); > return kvm_emulate_halt(vcpu); > } Why does the normal vcpu entry path fails to inject the interrupt? Because after halt, KVM_REQ_EVENT is not set?