From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932496AbcHKM5e (ORCPT ); Thu, 11 Aug 2016 08:57:34 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:34452 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751862AbcHKM5c (ORCPT ); Thu, 11 Aug 2016 08:57:32 -0400 Subject: Re: [PATCH] vfio: Enable VFIO device for powerpc To: Paul Mackerras , Alexander Graf References: <1439428546-13416-1-git-send-email-david@gibson.dropbear.id.au> <55DD8822.4060409@suse.de> <20150826185442.GB2662@fergus.ozlabs.ibm.com> Cc: 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 From: Paolo Bonzini Message-ID: Date: Thu, 11 Aug 2016 14:57:24 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20150826185442.GB2662@fergus.ozlabs.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Thanks, Paolo