From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 2/2][RFC] KVM: Emulate MSI-X table and PBA in kernel Date: Sun, 2 Jan 2011 12:39:28 +0200 Message-ID: <20110102103928.GA32272@redhat.com> References: <1293007495-32325-1-git-send-email-sheng@linux.intel.com> <4D1C5124.2090409@redhat.com> <20101230103256.GB6441@redhat.com> <201012311105.28371.sheng@linux.intel.com> <4D2052C3.3020901@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Sheng Yang , Marcelo Tosatti , kvm@vger.kernel.org, Alex Williamson To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:25611 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752762Ab1ABKkJ (ORCPT ); Sun, 2 Jan 2011 05:40:09 -0500 Content-Disposition: inline In-Reply-To: <4D2052C3.3020901@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Sun, Jan 02, 2011 at 12:26:11PM +0200, Avi Kivity wrote: > On 12/31/2010 05:05 AM, Sheng Yang wrote: > >> > >> Existing code does not support PBA in assigned devices, so at least it's > >> not a regression there, and the virtio spec says nothing about this so > >> we should be fine. > > > >I agree. At least it's not a regression. And in fact we haven't seen any device > >driver use this. I've checked Linux kernel code, found no one used PCI_MSIX_PBA or > >msix_pba_offset_reg(). > > > >I guess it's fine to get MSI-X mask part in first, then deal with PBA part if > >necessary - though we haven't seen any driver use it so far. It won't be worse > >with this patch anyway... > > In a way it is worse because before, the fix would belong in user > space, which is easier to test and distribute. Now we have to fix > it in the kernel. > > However I recognize that drivers which rely on the pending bit are > rare/nonexistent (likely on in preboot environments where interrupts > are hard), so even if we do code it, it will likely be incorrect > (certainly without a test). > > So I'll accept the patch without PBA. Michael, what about > supporting virtio? Can we base something on this patch? I don't see how userspace can send interrupts with this interface unfortunately. We also need irqfd support ... > -- > error compiling committee.c: too many arguments to function