From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cornelia Huck Subject: Re: [PATCH] vfio: Enable VFIO device for powerpc Date: Thu, 11 Aug 2016 15:19:57 +0200 Message-ID: <20160811151957.0f113a7c.cornelia.huck@de.ibm.com> References: <1439428546-13416-1-git-send-email-david@gibson.dropbear.id.au> <55DD8822.4060409@suse.de> <20150826185442.GB2662@fergus.ozlabs.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Paul Mackerras , Alexander Graf , David Gibson , alex.williamson@redhat.com, aik@ozlabs.ru, mdroth@linux.vnet.ibm.com, benh@kernel.crashing.org, mpe@ellerman.id.au, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, kvm-ppc To: Paolo Bonzini Return-path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:15981 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751268AbcHKNUK (ORCPT ); Thu, 11 Aug 2016 09:20:10 -0400 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u7BDFELK055750 for ; Thu, 11 Aug 2016 09:20:09 -0400 Received: from e06smtp10.uk.ibm.com (e06smtp10.uk.ibm.com [195.75.94.106]) by mx0a-001b2d01.pphosted.com with ESMTP id 24qm9ugqd5-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 11 Aug 2016 09:20:09 -0400 Received: from localhost by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 11 Aug 2016 14:20:06 +0100 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Thu, 11 Aug 2016 14:57:24 +0200 Paolo Bonzini wrote: > On 26/08/2015 20:54, Paul Mackerras wrote: > > On Wed, Aug 26, 2015 at 11:34:26AM +0200, Alexander Graf wrote: > >> On 13.08.15 03:15, David Gibson wrote: > >>> ec53500f "kvm: Add VFIO device" added a special KVM pseudo-device which is > >>> used to handle any necessary interactions between KVM and VFIO. > >>> > >>> Currently that device is built on x86 and ARM, but not powerpc, although > >>> powerpc does support both KVM and VFIO. This makes things awkward in > >>> userspace > >>> > >>> Currently qemu prints an alarming error message if you attempt to use VFIO > >>> and it can't initialize the KVM VFIO device. We don't want to remove the > >>> warning, because lack of the KVM VFIO device could mean coherency problems > >>> on x86. On powerpc, however, the error is harmless but looks disturbing, > >>> and a test based on host architecture in qemu would be ugly, and break if > >>> we do need the KVM VFIO device for something important in future. > >>> > >>> There's nothing preventing the KVM VFIO device from being built for > >>> powerpc, so this patch turns it on. It won't actually do anything, since > >>> we don't define any of the arch_*() hooks, but it will make qemu happy and > >>> we can extend it in future if we need to. > >>> > >>> Signed-off-by: David Gibson > >>> Reviewed-by: Eric Auger > > This patch (commit 178a787502123) did not select CONFIG_KVM_VFIO, so the > patch did nothing---except causing build failures which I fixed in > commit 0af574be32cdd ("KVM: PPC: do not compile in vfio.o > unconditionally", 2016-03-21) by making the patch a total no-op. > > Is KVM_VFIO really needed, and if so can this patch be fixed? FWIW, we enabled building vfio.o on s390 in 14b0b4a ("KVM: s390: Enable the KVM-VFIO device") with the rationale "while we don't need it, be like everybody else". Should powerpc (and every other architecture supporting kvm and vfio) select KVM_VFIO so that really everybody does the same thing?