From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:48930) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1goWej-0002U2-Od for qemu-devel@nongnu.org; Tue, 29 Jan 2019 11:54:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1goWeh-00022b-PG for qemu-devel@nongnu.org; Tue, 29 Jan 2019 11:54:37 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:56102 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1goWef-0001zg-RM for qemu-devel@nongnu.org; Tue, 29 Jan 2019 11:54:35 -0500 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x0TGoIej018650 for ; Tue, 29 Jan 2019 11:54:30 -0500 Received: from e06smtp02.uk.ibm.com (e06smtp02.uk.ibm.com [195.75.94.98]) by mx0b-001b2d01.pphosted.com with ESMTP id 2qasgb4n80-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 29 Jan 2019 11:54:30 -0500 Received: from localhost by e06smtp02.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 29 Jan 2019 16:54:28 -0000 Reply-To: pmorel@linux.ibm.com References: <20190121134249.16615-1-david@redhat.com> <20190121134249.16615-2-david@redhat.com> <7f7d8582-b6d2-b120-c768-8cc8350b416c@linux.ibm.com> <86377327-ab6d-df3a-b914-688206273bd5@redhat.com> From: Pierre Morel Date: Tue, 29 Jan 2019 17:54:24 +0100 MIME-Version: 1.0 In-Reply-To: <86377327-ab6d-df3a-b914-688206273bd5@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Message-Id: <14055713-cd8e-7fc5-d819-3724838662a3@linux.ibm.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v3 1/2] s390x/pci: Introduce unplug requests and split unplug handler List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Hildenbrand , qemu-devel@nongnu.org Cc: Thomas Huth , Cornelia Huck , Collin Walling , Christian Borntraeger , qemu-s390x@nongnu.org, Richard Henderson On 29/01/2019 16:14, David Hildenbrand wrote: > On 29.01.19 14:31, Pierre Morel wrote: >> On 21/01/2019 14:42, David Hildenbrand wrote: >>> PCI on s390x is really weird and how it was modeled in QEMU might not= have >>> been the right choice. Anyhow, right now it is the case that: >>> - Hotplugging a PCI device will silently create a zPCI device >>> (if none is provided) >>> - Hotunplugging a zPCI device will unplug the PCI device (if any) >>> - Hotunplugging a PCI device will unplug also the zPCI device >>> As far as I can see, we can no longer change this behavior. But we >>> should fix it. >> So unplugging PCI first will deny the guest any possibility to smoothl= y >> relinquish a device. >> >> >> Is it possible the other way around? >=20 > Maybe, but it does not really matter. We unplug both devices > synchronously, without the guest recognizing the order. We always have > the unplug request first that notifies the guest. When we get an ACK > from the guest, we can unpplug both devices in any order. >=20 > (and if we want to change the order, we should do it in a separate > patch, this patch does not change the order, just refactors the code) If it is done atomically, then I have no objection. Regards, Pierre --=20 Pierre Morel Linux/KVM/QEMU in B=C3=B6blingen - Germany