From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH 1/2] KVM: x86 emulator: don't update vcpu state if instruction is restarted. Date: Sun, 1 Aug 2010 12:24:38 +0300 Message-ID: <20100801092438.GE24773@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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: mtosatti@redhat.com, kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:3388 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753305Ab0HAJYj (ORCPT ); Sun, 1 Aug 2010 05:24:39 -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 o719OdVq029914 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Sun, 1 Aug 2010 05:24:39 -0400 Content-Disposition: inline In-Reply-To: <4C553B00.8030100@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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. > > >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. -- Gleb.