From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 1/2] KVM: x86 emulator: don't update vcpu state if instruction is restarted. Date: Sun, 01 Aug 2010 13:00:11 +0300 Message-ID: <4C5545AB.3080806@redhat.com> References: <1280405513-579-1-git-send-email-gleb@redhat.com> <1280405513-579-2-git-send-email-gleb@redhat.com> <4C545C79.1010102@redhat.com> <20100801082815.GC24773@redhat.com> <4C55364E.9090605@redhat.com> <20100801090145.GD24773@redhat.com> <4C553B00.8030100@redhat.com> <20100801092438.GE24773@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: mtosatti@redhat.com, kvm@vger.kernel.org To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:59422 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753905Ab0HAKAO (ORCPT ); Sun, 1 Aug 2010 06:00:14 -0400 Received: from int-mx08.intmail.prod.int.phx2.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o71A0DqI028195 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Sun, 1 Aug 2010 06:00:13 -0400 Received: from cleopatra.tlv.redhat.com (cleopatra.tlv.redhat.com [10.35.255.11]) by int-mx08.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o71A0CBV028138 for ; Sun, 1 Aug 2010 06:00:12 -0400 In-Reply-To: <20100801092438.GE24773@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 08/01/2010 12:24 PM, Gleb Natapov wrote: > On Sun, Aug 01, 2010 at 12:14:40PM +0300, Avi Kivity wrote: >> On 08/01/2010 12:01 PM, Gleb Natapov wrote: >>>>> It uses rip _during_ pio. And pio emulation changes rip >>>>> only at the end of emulation. >>>> But non-emulated pio does a skip_emulated_instruction() immediately >>>> (or so the code in kvm-tpr-opt.c assumes: >>>> >>> Indeed, this is bug in non-emulated pio. >> But userspace depends on this bug. > We can fix that, or make it smarter. Look for io instruction at > rip/rip-2 and use rip accordingly for instance. That requires everyone to update, or suffer major breakage. >>> But the patch does not change >>> rip behaviour for emulated pio. vcpu->arch.emulate_ctxt.eip is updated >>> only at the end of emulation. >> That will lead to failures if the emulator is used for the >> kvm-tpr-opt pio (which may happen with big real mode). >> > IIRC it was always this way in emulator. I'd rather fix userspace than > break emulator. It wasn't a problem because the emulator wasn't (and still isn't) used for this. But it has the potential to break badly once we make emulate_invalid_guest_state=1 the default. -- error compiling committee.c: too many arguments to function