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 15:23:16 +0300 Message-ID: <20100801122316.GG24773@redhat.com> References: <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> <4C5545AB.3080806@redhat.com> <20100801105337.GF24773@redhat.com> <4C5565C6.1090004@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]:45783 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753238Ab0HAMXU (ORCPT ); Sun, 1 Aug 2010 08:23:20 -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 o71CNKPa005753 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Sun, 1 Aug 2010 08:23:20 -0400 Content-Disposition: inline In-Reply-To: <4C5565C6.1090004@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Sun, Aug 01, 2010 at 03:17:10PM +0300, Avi Kivity wrote: > On 08/01/2010 01:53 PM, Gleb Natapov wrote: > > > >>That requires everyone to update, or suffer major breakage. > >> > >They will suffer major breakage when they update to a kvm that calls to > >kvm-tpr-opt.c from emulator anyway. > > Why? > Because tpr code will be called with wrong rip. Emulator always updated rip at the end of an instruction emulation in writeback stage. > >>>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. > >> > >So what can we do about it? > > > > Keep the existing behaviour. > Existing behaviour will cause breakage. -- Gleb.