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Wed, 1 Apr 2026 16:28:58 +0000 (GMT) Message-ID: Date: Wed, 1 Apr 2026 09:28:57 -0700 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 v8 2/3] vfio/ism: Implement vfio_pci driver for ISM devices To: Julian Ruess , schnelle@linux.ibm.com, wintera@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, 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: <20260325-vfio_pci_ism-v8-0-ddc504cde914@linux.ibm.com> <20260325-vfio_pci_ism-v8-2-ddc504cde914@linux.ibm.com> Content-Language: en-US From: Farhan Ali In-Reply-To: <20260325-vfio_pci_ism-v8-2-ddc504cde914@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDAxMDE1MiBTYWx0ZWRfXwiDqhZdR7r2b 2NeRzSts7j1FXaM+q1fLgqbT48zd1+k7VdnOq6xA8kmwEkPOLLBFCW+pGCs0iHDJmzvDU39055k LXkfSexkVXZyhAq6cj2j0LLh49DYV7Q6pegGgoQ2nwrsrLtYcawtydTxd4brFfhv83WTQkPKsyW ifA8IrS+X8WnsShS9kBnKY4fpbpGI+7DdJDKoxpmRk9n0SHXUyMdmGrwN4WxisHttBPRo/WCSE/ Q0EETLleHswEmgOZgIWrqZJ8QmSfxs1mMap4F94rKazS3pa65uC9WtOOKwFmO4CEqSTX7sVtFgS KIQ70MVUnPlHZgXIEOKO76EhZpwP5kr92aR1rPT2JP521uN6g2ardtuWMMe7wLNnLtdpYDngxMr 4N8/kVtRn4J6ludMUCM/dt74Haaktb57cwKBieYoZGt9uBfM+u8aUkTVg231s+keiphQCJzio98 DAP/J2od+V1BV6RPawg== X-Authority-Analysis: v=2.4 cv=QKZlhwLL c=1 sm=1 tr=0 ts=69cd47ce cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=akap8JHnbm7pTVdsz3UA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: bfWW_YluBv6JnohcvqC4Kb3bOE2DEqql X-Proofpoint-ORIG-GUID: bfWW_YluBv6JnohcvqC4Kb3bOE2DEqql 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=2026-04-01_04,2026-04-01_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 phishscore=0 adultscore=0 impostorscore=0 clxscore=1015 spamscore=0 bulkscore=0 priorityscore=1501 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2604010152 On 3/25/2026 6:31 AM, 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. > > 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. > > Reviewed-by: Alexandra Winter > Reviewed-by: Niklas Schnelle > Signed-off-by: Julian Ruess > --- I think we have decided to not support any additional regions with this patch. Feel free to add Reviewed-by: Farhan Ali