From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [Qemu-devel] KVM: Windows 64-bit troubles with user space irqchip Date: Thu, 03 Feb 2011 10:32:25 +0100 Message-ID: <4D4A7629.1010506@siemens.com> References: <4D4946F7.1070702@siemens.com> <20110202123532.GF14984@redhat.com> <4D4952FA.8020300@siemens.com> <4D49569F.6060207@redhat.com> <4D496A8D.90000@siemens.com> <4D496BC5.10807@redhat.com> <4D496D77.2010405@siemens.com> <4D496FA6.8070301@siemens.com> <4D49738D.7080404@redhat.com> <4D4979BD.6080900@siemens.com> <20110202154611.GR14984@redhat.com> <4D497DAB.7010901@siemens.com> <4D4A64F2.8010309@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Gleb Natapov , kvm , qemu-devel To: Avi Kivity Return-path: Received: from thoth.sbs.de ([192.35.17.2]:34137 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755479Ab1BCJcl (ORCPT ); Thu, 3 Feb 2011 04:32:41 -0500 In-Reply-To: <4D4A64F2.8010309@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2011-02-03 09:18, Avi Kivity wrote: > On 02/02/2011 05:52 PM, Jan Kiszka wrote: >>>> >>> If there is no problem in the logic of this commit (and I do not see >>> one yet) then we somewhere miss kicking vcpu when interrupt, that should be >>> handled, arrives? >> >> I'm not yet confident about the logic of the kernel patch: mov to cr8 is >> serializing. If the guest raises the tpr and then signals this with a >> succeeding, non vm-exiting instruction to the other vcpus, one of those >> could inject an interrupt with a higher priority than the previous tpr, >> but a lower one than current tpr. QEMU user space would accept this >> interrupt - and would likely surprise the guest. Do I miss something? > > apic_get_interrupt() is only called from the vcpu thread, so it should > see a correct tpr. > > The only difference I can see with the patch is that we may issue a > spurious cpu_interrupt(). But that shouldn't do anything bad, should it? I tested this yesterday, and it doesn't confuse Windows. It actually receives quite a few spurious IRQs in normal operation, w/ or w/o the kernel's tpr optimization. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux