Messages in this thread | | | Subject | Re: [PATCH 4/4] vfio-pci/zdev: Introduce the zPCI I/O vfio region | From | Matthew Rosato <> | Date | Thu, 21 Jan 2021 10:57:12 -0500 |
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On 1/21/21 5:01 AM, Niklas Schnelle wrote: > > > 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@linux.ibm.com> >> --- >> 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. >
This is a fair point, but just to tie up threads here -- the QEMU discussion has since moved towards making the use-case less restrictive rather than ISM-only (though getting ISM working is still the motivating factor here). So as such I think I'd prefer to keep this in vfio_pci_zdev.c as other hardware could use the region if they meet the necessary criteria.
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