Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935442Ab3FTIsZ (ORCPT ); Thu, 20 Jun 2013 04:48:25 -0400 Received: from mail-ie0-f174.google.com ([209.85.223.174]:64721 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754945Ab3FTIsW (ORCPT ); Thu, 20 Jun 2013 04:48:22 -0400 Message-ID: <51C2C1CC.9000003@ozlabs.ru> Date: Thu, 20 Jun 2013 18:48:12 +1000 From: Alexey Kardashevskiy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6 MIME-Version: 1.0 To: Benjamin Herrenschmidt CC: David Gibson , Alex Williamson , Alexander Graf , linuxppc-dev@lists.ozlabs.org, Paul Mackerras , "kvm@vger.kernel.org mailing list" , open list , kvm-ppc@vger.kernel.org, Rusty Russell , Joerg Roedel Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling References: <1371422343.21896.143.camel@pasglop> <1371438800.22681.38.camel@ul30vt.home> <1371441361.21896.152.camel@pasglop> <1371522772.22681.140.camel@ul30vt.home> <87txkun568.fsf@rustcorp.com.au> <1371617970.21896.232.camel@pasglop> <1371653443.21896.291.camel@pasglop> <1371656989.22659.98.camel@ul30vt.home> <51C28BEA.8050501@ozlabs.ru> <20130620052822.GB3140@voom.redhat.com> <1371714449.3944.14.camel@pasglop> In-Reply-To: <1371714449.3944.14.camel@pasglop> Content-Type: text/plain; charset=KOI8-R Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1296 Lines: 34 On 06/20/2013 05:47 PM, Benjamin Herrenschmidt wrote: > On Thu, 2013-06-20 at 15:28 +1000, David Gibson wrote: >>> Just out of curiosity - would not get_file() and fput_atomic() on a >> group's >>> file* do the right job instead of vfio_group_add_external_user() and >>> vfio_group_del_external_user()? >> >> I was thinking that too. Grabbing a file reference would certainly be >> the usual way of handling this sort of thing. > > But that wouldn't prevent the group ownership to be returned to > the kernel or another user would it ? Holding the file pointer does not let the group->container_users counter go to zero and this is exactly what vfio_group_add_external_user() and vfio_group_del_external_user() do. The difference is only in absolute value - 2 vs. 3. No change in behaviour whether I use new vfio API or simply hold file* till KVM closes fd created when IOMMU was connected to LIOBN. And while this counter is not zero, QEMU cannot take ownership over the group. I am definitely still missing the bigger picture... -- Alexey -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/