Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752311AbdHQMPN (ORCPT ); Thu, 17 Aug 2017 08:15:13 -0400 Received: from mail-wr0-f174.google.com ([209.85.128.174]:33777 "EHLO mail-wr0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750957AbdHQMPK (ORCPT ); Thu, 17 Aug 2017 08:15:10 -0400 Subject: Re: [PATCH] kvm: x86: disable KVM_FAST_MMIO_BUS From: Paolo Bonzini To: "Michael S. Tsirkin" Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org References: <20170816112249.28939-1-pbonzini@redhat.com> <20170816155132-mutt-send-email-mst@kernel.org> <9de5ebf5-457d-2a34-0314-c6c612ddb2e9@redhat.com> <20170816161301-mutt-send-email-mst@kernel.org> <20170816194342-mutt-send-email-mst@kernel.org> <81dabc78-edfd-32fc-024c-c57330386a51@redhat.com> <20170816190316.GA2566@flask> <20170816224815-mutt-send-email-mst@kernel.org> <20170817011815-mutt-send-email-mst@kernel.org> <2e42e64c-f31d-5ccd-2357-1a859cec5b5b@redhat.com> Message-ID: <2f80e82b-3007-0348-72b8-3391c7c57589@redhat.com> Date: Thu, 17 Aug 2017 14:14:59 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <2e42e64c-f31d-5ccd-2357-1a859cec5b5b@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 961 Lines: 23 On 17/08/2017 11:00, Paolo Bonzini wrote: > On 17/08/2017 00:31, Michael S. Tsirkin wrote: >> On Wed, Aug 16, 2017 at 11:25:35PM +0200, Paolo Bonzini wrote: >>> Yes, I agree. EMULTYPE_SKIP is fine because failed decoding still >>> causes an exception to be injected. Maybe it's better to gate the >>> EMULTYPE_SKIP emulation on the exit qualification saying this is a write >> >> I thought it's already limited to writes. I agree that's a reasonable >> limitation in any case. >> >>> and also not a page table walk---just in case. >> >> I still don't get it, sorry. Let's assume for the sake of argument >> that it's a PT walk causing the MMIO access. Just why do you think >> that it makes sense to skip the instruction that caused the walk? > > I think it doesn't. I think in that case it's better to skip the fast > write and proceed with full emulation. ... nope, exit qualification is just zero for EPT misconfigurations, so we cannot do this. Paolo