Today, ISM devices are completely disallowed for vfio-pci passthrough as QEMU rejects the device due to an (inappropriate) MSI-X check. Removing this fence, however, reveals additional deficiencies in the s390x PCI interception layer that prevent ISM devices from working correctly. Namely, ISM block write operations have particular requirements in regards to the alignment, size and order of writes performed that cannot be guaranteed when breaking up write operations through the typical vfio_pci_bar_rw paths. Furthermore, ISM requires 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.
This patchset provides a set of fixes related to enabling ISM device passthrough and includes patches to enable use of a new vfio region that will allow s390x PCI pass-through devices to perform s390 PCI instructions in such a way that the same instruction issued on the guest is re-issued on the host. The region is intended for use with ISM devices specifically, as they do not implement MSI-X and thus transferring I/O in this manner will not interfere with vfio-pci MSI-X masking. If someone can think of a good way to also make this MSI-X compatible (and thus usable by other device types besides ISM), I'm open to suggestions... Associated kernel patchset: https://lkml.org/lkml/2020/12/9/1059 Matthew Rosato (8): linux-headers: update against 5.10-rc7 s390x/pci: MSI-X isn't strictly required for passthrough s390x/pci: fix pcistb length s390x/pci: Introduce the ZpciOps structure s390x/pci: Fix memory_region_access_valid call s390x/pci: Handle devices that support relaxed alignment s390x/pci: PCISTB via the vfio zPCI I/O region s390x/pci: PCILG via the vfio zPCI I/O region hw/s390x/s390-pci-bus.c | 32 ++- hw/s390x/s390-pci-inst.c | 289 ++++++++++++++------- hw/s390x/s390-pci-vfio.c | 164 ++++++++++++ include/hw/s390x/s390-pci-bus.h | 24 ++ include/hw/s390x/s390-pci-clp.h | 1 + include/hw/s390x/s390-pci-inst.h | 3 + include/hw/s390x/s390-pci-vfio.h | 23 ++ include/standard-headers/asm-x86/kvm_para.h | 1 + .../infiniband/hw/vmw_pvrdma/pvrdma_verbs.h | 2 +- include/standard-headers/linux/vhost_types.h | 9 + linux-headers/linux/vfio.h | 4 + linux-headers/linux/vfio_zdev.h | 33 +++ linux-headers/linux/vhost.h | 4 + 13 files changed, 486 insertions(+), 103 deletions(-) -- 1.8.3.1
