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Tue, 25 Feb 2025 08:59:18 GMT Received: from smtpav03.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 514205805A; Tue, 25 Feb 2025 08:59:18 +0000 (GMT) Received: from smtpav03.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5F7965805D; Tue, 25 Feb 2025 08:59:14 +0000 (GMT) Received: from [9.171.91.87] (unknown [9.171.91.87]) by smtpav03.wdc07v.mail.ibm.com (Postfix) with ESMTP; Tue, 25 Feb 2025 08:59:14 +0000 (GMT) Message-ID: <7bcd6de5f40b2ee6d4d6758e3d2473172bd9b990.camel@linux.ibm.com> Subject: Re: [PATCH v6 0/3] vfio/pci: s390: Fix issues preventing VFIO_PCI_MMAP=y for s390 and enable it From: Niklas Schnelle To: Bjorn Helgaas Cc: Christoph Hellwig , Alexandra Winter , Alex Williamson , Gerd Bayer , Matthew Rosato , Jason Gunthorpe , Thorsten Winkler , Bjorn Helgaas , Julian Ruess , Halil Pasic , Christian Borntraeger , Sven Schnelle , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-pci@vger.kernel.org Date: Tue, 25 Feb 2025 09:59:13 +0100 In-Reply-To: <20250224205314.GA478317@bhelgaas> References: <20250224205314.GA478317@bhelgaas> Autocrypt: addr=schnelle@linux.ibm.com; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: oLFPjSzyp6gQNtF5PwA-vF2Ohd1XdAH1 X-Proofpoint-ORIG-GUID: P3H2XF625KdDvvOt1mMRoJsXJvEAF0M_ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-02-25_03,2025-02-24_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=974 mlxscore=0 malwarescore=0 spamscore=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 suspectscore=0 phishscore=0 clxscore=1015 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502100000 definitions=main-2502250061 On Mon, 2025-02-24 at 14:53 -0600, Bjorn Helgaas wrote: > On Fri, Feb 14, 2025 at 02:10:51PM +0100, Niklas Schnelle wrote: > > With the introduction of memory I/O (MIO) instructions enbaled in commi= t > > 71ba41c9b1d9 ("s390/pci: provide support for MIO instructions") s390 > > gained support for direct user-space access to mapped PCI resources. > > Even without those however user-space can access mapped PCI resources > > via the s390 specific MMIO syscalls. There is thus nothing fundamentall= y > > preventing s390 from supporting VFIO_PCI_MMAP, allowing user-space > > drivers to access PCI resources without going through the pread() > > interface. To actually enable VFIO_PCI_MMAP a few issues need fixing > > however. > >=20 > > Firstly the s390 MMIO syscalls do not cause a page fault when > > follow_pte() fails due to the page not being present. This breaks > > vfio-pci's mmap() handling which lazily maps on first access. > >=20 > > Secondly on s390 there is a virtual PCI device called ISM which has > > a few oddities. For one it claims to have a 256 TiB PCI BAR (not a typo= ) > > which leads to any attempt to mmap() it fail with the following message= : > >=20 > > vmap allocation for size 281474976714752 failed: use vmalloc=3D to increase size > >=20 > > Even if one tried to map this BAR only partially the mapping would not > > be usable on systems with MIO support enabled. So just block mapping > > BARs which don't fit between IOREMAP_START and IOREMAP_END. Solve this > > by keeping the vfio-pci mmap() blocking behavior around for this > > specific device via a PCI quirk and new pdev->non_mappable_bars > > flag. > >=20 > > As noted by Alex Williamson With mmap() enabled in vfio-pci it makes > > sense to also enable HAVE_PCI_MMAP with the same restriction for pdev-> > > non_mappable_bars. So this is added in patch 3 and I tested this with > > another small test program. > >=20 > > Note: > > For your convenience the code is also available in the tagged > > b4/vfio_pci_mmap branch on my git.kernel.org site below: > > https://git.kernel.org/pub/scm/linux/kernel/git/niks/linux.git/ > >=20 > > Thanks, > > Niklas > >=20 > > Link: https://lore.kernel.org/all/c5ba134a1d4f4465b5956027e6a4ea6f6beff= 969.camel@linux.ibm.com/ > > Signed-off-by: Niklas Schnelle > > --- > > Changes in v6: > > - Add a patch to also enable PCI resource mmap() via sysfs and proc > > exlcluding pdev->non_mappable_bars devices (Alex Williamson) > > - Added Acks > > - Link to v5: https://lore.kernel.org/r/20250212-vfio_pci_mmap-v5-0-633= ca5e056da@linux.ibm.com >=20 > I think the series would be more readable if patch 2/3 included all > the core changes (adding pci_dev.non_mappable_bars, the 3/3 > pci-sysfs.c and proc.c changes to test it, and I suppose the similar > vfio_pci_core.c change), and we moved all the s390 content from 2/3 to > 3/3. Maybe we could do the following: 1/3: As is 2/3: Introduces pdev->non_mappable_bars and the checks in vfio and proc.c/pci-sysfs.c. To make the flag handle the vfio case with VFIO_PCI_MMAP gone, a one-line change in s390 will set pdev- >non_mappable_bars =3D 1 for all PCI devices. 3/3: Changes setting pdev->non_mappable_bars =3D 1 in s390 to only the ISM device using the quirk handling and adds HAVE_PCI_MMAP. Thanks, Niklas