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

Matthew Rosato
2020-12-09T20:53:32Z

On 12/9/20 3:27 PM, Matthew Rosato wrote:
> 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(-)
>