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Subject: Re: [RFC 0/4] vfio-pci/zdev: Fixing s390 vfio-pci ISM support
From:   Matthew Rosato <mjrosato@linux.ibm.com>
To:     alex.williamson@redhat.com, cohuck@redhat.com,
        schnelle@linux.ibm.com
Cc:     pmorel@linux.ibm.com, borntraeger@de.ibm.com, hca@linux.ibm.com,
        gor@linux.ibm.com, gerald.schaefer@linux.ibm.com,
        linux-s390@vger.kernel.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1607545670-1557-1-git-send-email-mjrosato@linux.ibm.com>
Message-ID: <765a8b73-a879-ea96-d13e-8fd574b363be@linux.ibm.com>
Date:   Wed, 9 Dec 2020 15:52:43 -0500
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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(-)
> 

Associated qemu patchset:
https://lists.gnu.org/archive/html/qemu-devel/2020-12/msg02377.html