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Mon, 23 Mar 2026 13:59:10 +0000 (GMT) Message-ID: <8bfd4b31-96c8-4a7f-ba0e-9ab2b6a74bf1@linux.ibm.com> Date: Mon, 23 Mar 2026 14:59:09 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 2/3] vfio/ism: Implement vfio_pci driver for ISM devices To: Julian Ruess , schnelle@linux.ibm.com, ts@linux.ibm.com, oberpar@linux.ibm.com, gbayer@linux.ibm.com, Alex Williamson , Jason Gunthorpe , Yishai Hadas , Shameer Kolothum , Kevin Tian Cc: mjrosato@linux.ibm.com, alifm@linux.ibm.com, raspl@linux.ibm.com, hca@linux.ibm.com, agordeev@linux.ibm.com, gor@linux.ibm.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-pci@vger.kernel.org References: <20260323-vfio_pci_ism-v7-0-abf537150408@linux.ibm.com> <20260323-vfio_pci_ism-v7-2-abf537150408@linux.ibm.com> Content-Language: en-US From: Alexandra Winter In-Reply-To: <20260323-vfio_pci_ism-v7-2-abf537150408@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: P8Om7W6ApukN2-b0nyd1QTxrPj1CkLyU X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzIzMDEwNyBTYWx0ZWRfXyXy0lJ9b/UoM GfvcX5oOlUq06tDndhQ512wLqdILt6dfx7xtfADCWXphL5u5UdOEqz8ha6N2DA6s51tT7BFQVJm euv0ep3Psy23noOE07ALoe2yOS4OfwzFNVsS05pIh9tcpvy9yNPyGdDxgs/K6hPgqdkOYYFlSnW H/+5HdncyQrHYIXq7819CqX63Ysb6QZzJe0xt9RXjC9ZHubSqiyvPoCCk7ce9zx0zR/tYnn+Med M8oSGxyXLY5dBw7m21F5gqA3uPk2f3ccWO6JuAaBG+SuH/DD+tqGuZbSWtTMqjo7irg7Yh+/h4K sXrhOZHjpxk9mAKGDSAEPtJT57wbXeMgiLi6DAtfgAwDGlJZmrHnOC0q8brdkvYkR6Q7ggDFZ1V HQUYjxdQKCcWMISnNmEwA7ordDhZrz3OGt5b23vOxWfQomoaN+zpu+M9ZzbyXKWRK+w6VYytvxH D96Tsaygk/Nvm2u3D7Q== X-Proofpoint-GUID: P8Om7W6ApukN2-b0nyd1QTxrPj1CkLyU X-Authority-Analysis: v=2.4 cv=OsZCCi/t c=1 sm=1 tr=0 ts=69c14734 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=akap8JHnbm7pTVdsz3UA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-23_04,2026-03-20_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 adultscore=0 clxscore=1015 phishscore=0 suspectscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 spamscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603230107 On 23.03.26 10:32, Julian Ruess wrote: > Add a vfio_pci variant driver for the s390-specific Internal Shared > Memory (ISM) devices used for inter-VM communication. > > This enables the development of vfio-pci-based user space drivers for > ISM devices. > > On s390, kernel primitives such as ioread() and iowrite() are switched > over from function handle based PCI load/stores instructions to PCI > memory-I/O (MIO) loads/stores when these are available and not > explicitly disabled. Since these instructions cannot be used with ISM > devices, ensure that classic function handle-based PCI instructions are > used instead. > Nit: How do you want to spell "function-handle-based"? (You have one with 1 hyphen, one without) > The driver is still required even when MIO instructions are disabled, as > the ISM device relies on the PCI store block (PCISTB) instruction to > perform write operations. > > Stores are not fragmented, therefore one ioctl corresponds to exactly > one PCISTB instruction. User space must ensure to not write more than > 4096 bytes at once to an ISM BAR which is the maximum payload of the > PCISTB instruction. > > Signed-off-by: Julian Ruess > --- Looks good to me. Reviewed-by: Alexandra Winter