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List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: _nohi_2QuZKuEpacTUSbpWz2MLHPHFSh X-Proofpoint-ORIG-GUID: wg5GccEPjM00Ap0LJyncEYyYSYR-yxGy X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-04-19_11,2024-04-19_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 impostorscore=0 clxscore=1011 suspectscore=0 malwarescore=0 mlxlogscore=648 adultscore=0 priorityscore=1501 mlxscore=0 phishscore=0 lowpriorityscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2404010000 definitions=main-2404190121 On Fri, 2024-04-19 at 10:58 -0300, Jason Gunthorpe wrote: > On Fri, Apr 19, 2024 at 03:53:23PM +0200, Gerd Bayer wrote: > > From: Ben Segal > >=20 > > Many PCI adapters can benefit or even require full 64bit read > > and write access to their registers. In order to enable work on > > user-space drivers for these devices add two new variations > > vfio_pci_core_io{read|write}64 of the existing access methods > > when the architecture supports 64-bit ioreads and iowrites. > >=20 > > Signed-off-by: Ben Segal > > Co-developed-by: Gerd Bayer > > Signed-off-by: Gerd Bayer > > --- > >=20 > > Hi all, > >=20 > > we've successfully used this patch with a user-mode driver for a PCI > > device that requires 64bit register read/writes on s390. >=20 > But why? S390 already has a system call for userspace to do the 64 bit > write, and newer S390 has a userspace instruction to do it. >=20 > Why would you want to use a VFIO system call on the mmio emulation > path? >=20 > mmap the registers and access them normally? It's a very good point and digging into why this wasn't used by Benjamin. It turns out VFIO_PCI_MMAP is disabled for S390 which it really shouldn't be especially now that we have the user-space instructions. Before that though Benjamin turned to this interface which then lead him to this limitation. So yeah we'll definitely verify that it also works via VFIO_PCI_MMAP and send a patch to enable that. That said I still think it's odd not to have the 8 byte case working here even if it isn't the right approach. Could still be useful for debug/testing without having to add the MIO instructions or the our special syscall. Thanks, Niklas