From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41822) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dxBQh-0004fy-SW for qemu-devel@nongnu.org; Wed, 27 Sep 2017 08:27:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dxBQc-00065O-4D for qemu-devel@nongnu.org; Wed, 27 Sep 2017 08:27:07 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:58824) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dxBQb-00065C-QS for qemu-devel@nongnu.org; Wed, 27 Sep 2017 08:27:02 -0400 Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v8RCOTCX048226 for ; Wed, 27 Sep 2017 08:26:57 -0400 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0a-001b2d01.pphosted.com with ESMTP id 2d8bcaaeff-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 27 Sep 2017 08:26:56 -0400 Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 27 Sep 2017 13:26:54 +0100 References: <20170926162058.30772-1-cohuck@redhat.com> <20170926162058.30772-2-cohuck@redhat.com> <338c8565-691e-a8bc-d8a6-3637ce13701d@redhat.com> <20170927114717.72bd69f8.cohuck@redhat.com> <20170927125606.65dc514d.cohuck@redhat.com> <14df9ad6-f0e9-cd51-04dd-4fe994808433@de.ibm.com> <4681e677-9e5a-4c1c-8e22-dc5c51b7286d@redhat.com> From: Christian Borntraeger Date: Wed, 27 Sep 2017 14:26:50 +0200 MIME-Version: 1.0 In-Reply-To: <4681e677-9e5a-4c1c-8e22-dc5c51b7286d@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Message-Id: <090b28f2-de30-20ff-8458-2eb8184fcaeb@de.ibm.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Hildenbrand , Cornelia Huck , Yi Min Zhao Cc: qemu-devel@nongnu.org, agraf@suse.de, pasic@linux.vnet.ibm.com, jjherne@linux.vnet.ibm.com, dgilbert@redhat.com On 09/27/2017 02:21 PM, David Hildenbrand wrote: > On 27.09.2017 12:59, Christian Borntraeger wrote: >> >> >> On 09/27/2017 12:56 PM, Cornelia Huck wrote: >>> On Wed, 27 Sep 2017 18:25:00 +0800 >>> Yi Min Zhao wrote: >>> >>>> =E5=9C=A8 2017/9/27 =E4=B8=8B=E5=8D=885:47, Cornelia Huck =E5=86=99=E9= =81=93: >>>>> On Tue, 26 Sep 2017 20:40:25 +0200 >>>>> David Hildenbrand wrote: >>> >>>>>> I'd really really really (did I mention really?) favor something l= ike a >>>>>> dummy device, because we could easily handle the !CONFIG_PCI case = then. >>>>>> >>>>>> All these compat options and conditions will kill us someday... we= 're >>>>>> already patching around that whole stuff way too much. >>>>>> >>>>>> If we ever unconditionally created a device, we should keep doing = so. =20 >>>>> Yes, that whole thing is horrible, especially interaction with comp= at >>>>> machines. >>>>> >>>>> Do you have an idea on how to create such a dummy device (without >>>>> having to effectively copy a lot of configured-out code)? >>>>> >>>>> =20 >>>> How about in s390_pcihost_hot_plug() we check s390_has_feat(zpci)? >>>> If no zpci feature, we avoid plugging any pci device. >>>> Then we could always create phb. >>>> I think pcibus's vmstate is only data to migrate. >>> >>> That's still problematic if CONFIG_PCI is off. I currently don't have= a >>> better idea than either disallowing compat machines on builds without >>> pci, or using a dummy device... >> >> For this particular case your initial patch might be less problematic = than >> a dummy device, because the code that does the migration is NOT contai= ned >> in s390 specific code but in common PCI code instead. We would need to= keep >> the dummy device always in a way that it will work with the common PCI >> code. >> >=20 > Interesting, so how is migration then handled for e.g. x86 or other > architectures that can work without CONFIG_PCI? I assume their migratio= n > should also break? If you migrate from a QEMU with CONFIG_PCI to a QEMU without CONFIG_PCI=20 I assume it will break. But maybe there is really some clever way to do the right thing.=20 PS: Is really anybody disabling CONFIG_PCI and why?