From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH 2/2] KVM: SVM: check for progress after IRET interception Date: Thu, 03 Feb 2011 17:30:56 +0100 Message-ID: <4D4AD840.4090906@siemens.com> References: <1296745369-12066-1-git-send-email-avi@redhat.com> <1296745369-12066-3-git-send-email-avi@redhat.com> <4D4AC4B5.7060009@redhat.com> <4D4AC7E3.7070408@siemens.com> <4D4ACA0D.4090707@redhat.com> <4D4ACFD9.9000203@siemens.com> <4D4AD0B7.4090809@redhat.com> <4D4AD481.1020603@siemens.com> <4D4AD5D3.1030706@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , "kvm@vger.kernel.org" , Joerg Roedel To: Avi Kivity Return-path: Received: from goliath.siemens.de ([192.35.17.28]:30332 "EHLO goliath.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932129Ab1BCQbN (ORCPT ); Thu, 3 Feb 2011 11:31:13 -0500 In-Reply-To: <4D4AD5D3.1030706@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2011-02-03 17:20, Avi Kivity wrote: > On 02/03/2011 06:14 PM, Jan Kiszka wrote: >> On 2011-02-03 16:58, Avi Kivity wrote: >>> On 02/03/2011 05:55 PM, Jan Kiszka wrote: >>>>> >>>>> What's an interrupt window without IRET interception? >>>> >>>> I don't the details, but I thought you could get something like an >>>> interrupt-window-open interception by (fake-)injecting an IRQ and >>>> intercepting on VIRQ acceptance. That will not work if returning to and >>>> staying in irq-disabled guest code, therefore the timeout, but it should >>>> be most efficient (specifically if the guest uses NMIs for things like >>>> perf). >>>> >>> >>> Since NMIs are used to break out of irq-disabled regions (watchdog, NMI >>> IPIs during reboots) I'm wary of such a solution. >> >> Right, but we already use it for Intel. The timeout ensures that you >> can't get stuck forever. I think Xen works this way as well (minus the >> timeout - last time I checked). > > Only without vnmi support, yes? In that case, we can't do any better. > In this case, we can, and we should, even at the expense of performance > or ridiculous complexity. OK, then I guess we should explore the single-step approach and make it waterproof. It's likely still much simpler than iret emulation. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux