From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 0/8][v2] MSI-X mask emulation support for assigned device Date: Wed, 20 Oct 2010 17:26:34 +0200 Message-ID: <4CBF0A2A.9010604@redhat.com> References: <1287563192-29685-1-git-send-email-sheng@linux.intel.com> <4CBEBB85.4000706@redhat.com> <20101020104447.GD12878@redhat.com> <4CBECB9E.7000005@redhat.com> <20101020134329.GB13311@redhat.com> <4CBF07EE.1000804@redhat.com> <1287588153.3007.35.camel@x201> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , Sheng Yang , Marcelo Tosatti , kvm@vger.kernel.org To: Alex Williamson Return-path: Received: from mx1.redhat.com ([209.132.183.28]:42282 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753859Ab0JTP0i (ORCPT ); Wed, 20 Oct 2010 11:26:38 -0400 In-Reply-To: <1287588153.3007.35.camel@x201> Sender: kvm-owner@vger.kernel.org List-ID: On 10/20/2010 05:22 PM, Alex Williamson wrote: > On Wed, 2010-10-20 at 17:17 +0200, Avi Kivity wrote: > > On 10/20/2010 03:43 PM, Michael S. Tsirkin wrote: > > > > >If instead of eventfd we had a file descriptor that can pass vector > > > > >information from vfio to kvm and back, that would fix it, > > > > >as we would not need to set us GSIs at all, > > > > >and not need for userspace to handle MSIX specially. > > > > > > > > > > > > > But if we emulate the entire msix bar in vfio, that's not needed, right? > > > > > > Yes, I think it is. How does kvm know which interrupt to inject? > > > Either vfio needs to pass that info to qemu and qemu would pass it > > > to kvm, or vfio would have some way to pass that info to kvm > > > directly. > > > > Wait. We can't emulate the BAR in vfio, we have to emulate it in kvm > > where we emulate the write instruction. We then need to tell vfio, > > perhaps via userspace, that masking state has changed. > > > > Seems very intrusive. > > We wouldn't direct map the vector table or pending bits, so we could > trap and emulate in qemu, which could then call into reads/writes in > vfio. > That's 100% unintrusive for kvm, but that's what we do today, which is deemed too slow. Another option is to fake an interrupt remapping device and do a direct map. Will those older guests recognize and use it? I imagine not. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.