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<4096cb9d402b1aabc9667d450221cb0922e78d90.camel@linux.ibm.com> Subject: Re: [PATCH v8 2/3] vfio/ism: Implement vfio_pci driver for ISM devices From: Niklas Schnelle To: Julian Ruess , 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, 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 In-Reply-To: <20260325-vfio_pci_ism-v8-2-ddc504cde914@linux.ibm.com> References: <20260325-vfio_pci_ism-v8-0-ddc504cde914@linux.ibm.com> <20260325-vfio_pci_ism-v8-2-ddc504cde914@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; prefer-encrypt=mutual; keydata=mQINBGHm3M8BEAC+MIQkfoPIAKdjjk84OSQ8erd2OICj98+GdhMQpIjHXn/RJdCZLa58k /ay5x0xIHkWzx1JJOm4Lki7WEzRbYDexQEJP0xUia0U+4Yg7PJL4Dg/W4Ho28dRBROoJjgJSLSHwc 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authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603260089 On Wed, 2026-03-25 at 14:31 +0100, Julian Ruess wrote: > Add a vfio_pci variant driver for the s390-specific Internal Shared > Memory (ISM) devices used for inter-VM communication. >=20 > This enables the development of vfio-pci-based user space drivers for > ISM devices. >=20 > 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. >=20 > 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. >=20 > 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. >=20 > Reviewed-by: Alexandra Winter > Reviewed-by: Niklas Schnelle > Signed-off-by: Julian Ruess > --- > drivers/vfio/pci/Kconfig | 2 + > drivers/vfio/pci/Makefile | 2 + > drivers/vfio/pci/ism/Kconfig | 10 ++ > drivers/vfio/pci/ism/Makefile | 3 + > drivers/vfio/pci/ism/main.c | 408 ++++++++++++++++++++++++++++++++++++= ++++++ > 5 files changed, 425 insertions(+) >=20 --- snip --- > + > +static int ism_vfio_pci_ioctl_get_region_info(struct vfio_device *core_v= dev, > + struct vfio_region_info *info, > + struct vfio_info_cap *caps) > +{ > + struct vfio_pci_core_device *vdev =3D > + container_of(core_vdev, struct vfio_pci_core_device, vdev); > + struct pci_dev *pdev =3D vdev->pdev; > + > + switch (info->index) { > + case VFIO_PCI_CONFIG_REGION_INDEX: > + info->offset =3D ISM_VFIO_PCI_INDEX_TO_OFFSET(info->index); > + info->size =3D pdev->cfg_size; > + info->flags =3D VFIO_REGION_INFO_FLAG_READ | > + VFIO_REGION_INFO_FLAG_WRITE; > + break; > + case VFIO_PCI_BAR0_REGION_INDEX ... VFIO_PCI_BAR5_REGION_INDEX: > + info->offset =3D ISM_VFIO_PCI_INDEX_TO_OFFSET(info->index); > + info->size =3D pci_resource_len(pdev, info->index); > + if (!info->size) { > + info->flags =3D 0; > + break; > + } > + info->flags =3D VFIO_REGION_INFO_FLAG_READ | > + VFIO_REGION_INFO_FLAG_WRITE; > + break; > + default: > + info->offset =3D 0; > + info->size =3D 0; > + info->flags =3D 0; > + return -EINVAL; Thinking more about this, the above default handling actually breaks additional regions such as the one added by Farhan for the error events. I think this needs to instead call the generic vfio_pci_ioctl_get_region_info() for other regions. > + } > + return 0; > +} --- snip ---