[RFC 0/4] vfio-pci/zdev: Fixing s390 vfio-pci ISM support

Matthew Rosato
2020-12-09T20:30:57Z

Today, ISM devices are completely disallowed for vfio-pci passthrough as
QEMU will reject the device due to an (inappropriate) MSI-X check.
However, in an effort to enable ISM device passthrough, I realized that the
manner in which ISM performs block write operations is highly incompatible
with the way that QEMU s390 PCI instruction interception and
vfio_pci_bar_rw break up I/O operations into 8B and 4B operations -- ISM
devices have particular requirements in regards to the alignment, size and
order of writes performed. Furthermore, they require that legacy/non-MIO
s390 PCI instructions are used, which is also not guaranteed when the I/O
is passed through the typical userspace channels.

As a result, this patchset proposes a new VFIO region to allow a guest to
pass certain PCI instruction intercepts directly to the s390 host kernel
PCI layer for exeuction, pinning the guest buffer in memory briefly in
order to execute the requested PCI instruction.

Matthew Rosato (4):
s390/pci: track alignment/length strictness for zpci_dev
vfio-pci/zdev: Pass the relaxed alignment flag
s390/pci: Get hardware-reported max store block length
vfio-pci/zdev: Introduce the zPCI I/O vfio region

arch/s390/include/asm/pci.h | 4 +-
arch/s390/include/asm/pci_clp.h | 7 +-
arch/s390/pci/pci_clp.c | 2 +
drivers/vfio/pci/vfio_pci.c | 8 ++
drivers/vfio/pci/vfio_pci_private.h | 6 ++
drivers/vfio/pci/vfio_pci_zdev.c | 160 ++++++++++++++++++++++++++++++++++++
include/uapi/linux/vfio.h | 4 +
include/uapi/linux/vfio_zdev.h | 33 ++++++++
8 files changed, 221 insertions(+), 3 deletions(-)

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1.8.3.1