On 1/19/21 9:02 PM, Matthew Rosato wrote: > Some s390 PCI devices (e.g. ISM) perform I/O operations that have very > specific requirements in terms of alignment as well as the patterns in > which the data is read/written. Allowing these to proceed through the > typical vfio_pci_bar_rw path will cause them to be broken in up in such a > way that these requirements can't be guaranteed. In addition, ISM devices > do not support the MIO codepaths that might be triggered on vfio I/O coming > from userspace; we must be able to ensure that these devices use the > non-MIO instructions. To facilitate this, provide a new vfio region by > which non-MIO instructions can be passed directly to the host kernel s390 > PCI layer, to be reliably issued as non-MIO instructions. > > This patch introduces the new vfio VFIO_REGION_SUBTYPE_IBM_ZPCI_IO region > and implements the ability to pass PCISTB and PCILG instructions over it, > as these are what is required for ISM devices. > > Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx> > --- > drivers/vfio/pci/vfio_pci.c | 8 ++ > drivers/vfio/pci/vfio_pci_private.h | 6 ++ > drivers/vfio/pci/vfio_pci_zdev.c | 158 ++++++++++++++++++++++++++++++++++++ > include/uapi/linux/vfio.h | 4 + > include/uapi/linux/vfio_zdev.h | 33 ++++++++ > 5 files changed, 209 insertions(+) Related to the discussion on the QEMU side, if we have a check to make sure this is only used for ISM, then this patch should make that clear in its wording and also in the paths (drivers/vfio/pci/vfio_pci_ism.c instead of vfio_pci_zdev.c.) This also has precedent with the region for IGD in drivers/vfio/pci/vfio_pci_igd.c.
