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Wed, 10 Jun 2020 21:37:58 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3007052051; Wed, 10 Jun 2020 21:37:58 +0000 (GMT) Received: from oc2783563651 (unknown [9.145.127.50]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id 8506B5204E; Wed, 10 Jun 2020 21:37:57 +0000 (GMT) Date: Wed, 10 Jun 2020 23:37:14 +0200 From: Halil Pasic To: David Gibson Subject: Re: [PATCH v2 1/1] virtio-ccw: auto-manage VIRTIO_F_IOMMU_PLATFORM if PV Message-ID: <20200610233714.05174c93.pasic@linux.ibm.com> In-Reply-To: <20200610042554.GD494336@umbus.fritz.box> References: <20200514221155.32079-1-pasic@linux.ibm.com> <20200520121507-mutt-send-email-mst@kernel.org> <20200606013217.2cffa3ed.pasic@linux.ibm.com> <20200608181428.3c6f127c.cohuck@redhat.com> <20200608190045.319dd68b.pasic@linux.ibm.com> <20200609084402.35d317ec.cohuck@redhat.com> <20200610042554.GD494336@umbus.fritz.box> Organization: IBM X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/hnp6abtT+3frwSu.euV9H7q"; protocol="application/pgp-signature" X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216, 18.0.687 definitions=2020-06-10_13:2020-06-10, 2020-06-10 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 clxscore=1015 priorityscore=1501 spamscore=0 mlxscore=0 impostorscore=0 cotscore=-2147483648 bulkscore=0 suspectscore=0 lowpriorityscore=0 adultscore=0 phishscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006100155 Received-SPF: pass client-ip=148.163.158.5; envelope-from=pasic@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/10 17:38:08 X-ACL-Warn: Detected OS = Linux 3.x [generic] [fuzzy] X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Thomas Huth , Boris Fiuczynski , Janosch Frank , Pierre Morel , "Michael S. Tsirkin" , Cornelia Huck , David Hildenbrand , qemu-devel@nongnu.org, Christian Borntraeger , qemu-s390x@nongnu.org, Viktor Mihajlovski , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --Sig_/hnp6abtT+3frwSu.euV9H7q Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Wed, 10 Jun 2020 14:25:54 +1000 David Gibson wrote: > > > I'm going to definitely have a good look at that. What I think special > > > about s390 is that F_ACCESS_PLATFORM is hurting us because all IO nee= ds > > > to go through ZONE_DMA (this is a problem of the implementation that > > > stemming form a limitation of the DMA API, upstream didn't let me > > > fix it). =20 > >=20 > > My understanding is that power runs into similar issues, but I don't > > know much about power, so I might be entirely wrong :) =20 >=20 > Sort of, but not to the same extent, I think. I'm curious what are the ramifications of a misguided hotplug on POWER? Does using F_ACCESS_PLATFORM when it isn't required have any significant drawbacks, or are you fine to just go with the safe option? 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