From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Williamson Subject: Re: [PATCH 0/8][v2] MSI-X mask emulation support for assigned device Date: Wed, 20 Oct 2010 09:22:33 -0600 Message-ID: <1287588153.3007.35.camel@x201> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , Sheng Yang , Marcelo Tosatti , kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:30729 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753217Ab0JTPWf (ORCPT ); Wed, 20 Oct 2010 11:22:35 -0400 In-Reply-To: <4CBF07EE.1000804@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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. Alex > We can perhaps use the new semaphore capability in eventfd to pass > mask/unmask information from kvm to userspace. We'd usually hook it to > the corresponding vfio facility. > > > > How far away is vfio? If it's merged soon, we might avoid making > > > changes to the old assigned device infrastructure and instead update > > > vfio. > > > > Hard to be sure, hopefully 2.6.38 material. > > My question was how to implement this with vfio. But your list is > interesting as well. > >