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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 <wintera@linux.ibm.com> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com> Signed-off-by: Julian Ruess <julianr@linux.ibm.com> Reviewed-by: Farhan Ali <alifm@linux.ibm.com> Link: https://lore.kernel.org/r/20260325-vfio_pci_ism-v8-2-ddc504cde914@linux.ibm.com Signed-off-by: Alex Williamson <alex@shazbot.org>
4 lines
105 B
Makefile
4 lines
105 B
Makefile
# SPDX-License-Identifier: GPL-2.0
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obj-$(CONFIG_ISM_VFIO_PCI) += ism-vfio-pci.o
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ism-vfio-pci-y := main.o
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