ACK: [SRU][U/N][M][L][PATCH v2 0/1] Kernel config option missing for s390x PCI passthrough (LP: 2042853)

[Manuel Diewald]

On Tue, Nov 21, 2023 at 01:54:47PM +0100, frank.heimes at canonical.com wrote:
> BugLink: https://bugs.launchpad.net/bugs/2042853
> 
> SRU Justification:
> 
> [Impact]
> 
>  * Today no s390x-specific vfio-pci devices (zPCI) can be passed
>    from a KVM host to a KVM guest (incl. secure execution guests
>    in the context of confidential computing).
> 
>  * s390x PCI passthrough needs various changes in the s390x kernel zPCI
>    code (incl. the new s390x-specific Kernel config option
>    'CONFIG_VFIO_PCI_ZDEV_KVM') that were introduced with kernel 6.0
>    and got backported to 22.04/jammy as part of LP: #1853306.
> 
>  * Lunar an newer Ubuntu releases have the code already included from
>    upstream (incl. the Kernel option 'CONFIG_VFIO_PCI_ZDEV_KVM'), but the
>    config option is not set, hence zPCI pass-through is still not possible.
> 
> [Fix]
> 
>  * To be able to make use of VFIO zPCI pass-through on s390x running newer
>    Ubuntu releases (especially needed in the context of secure execution)
>    the (s390x-specific) Kernel config option 'CONFIG_VFIO_PCI_ZDEV_KVM' needs
>    to be enabled and set to 'y'.
> 
> [Test Case]
> 
>  * Hardware used: z14 or greater LPAR, PCI-attached devices
>    (RoCE VFs, ISM devices, NVMe drive)
> 
>  * Setup: Both the kernel and QEMU features are needed for the feature
>    to function (an upstream QEMU can be used to verify the kernel early),
>    and the facility is only available on z14 or newer.
>    When any of those pieces is missing,
>    the interpretation facility will not be used.
>    When both the kernel and QEMU features are included in their respective
>    packages, and running in an LPAR on a z14 or newer machine,
>    this feature will be enabled automatically.
>    Existing supported devices should behave as before with no changes
>    required by an end-user (e.g. no changes to libvirt domain definitions)
>    -- but will now make use of the interpretation facility.
>    Additionally, ISM devices will now be eligible for vfio-pci passthrough
>    (where before QEMU would exit on error if attempting to provide an ISM
>    device for vfio-pci passthrough, preventing the guest from starting)
> 
>  * Testing will include the following scenarios, repeated each for RoCE,
>    ISM and NVMe:
> 
>    1) Testing of basic device passthrough (create a VM with a vfio-pci
>       device as part of the libvirt domain definition, passing through
>       a RoCE VF, an ISM device, or an NVMe drive. Verify that the device
>       is available in the guest and functioning)
>    2) Testing of device hotplug/unplug (create a VM with a vfio-pci device,
>       virsh detach-device to remove the device from the running guest,
>       verify the device is removed from the guest, then virsh attach-device
>       to hotplug the device to the guest again, verify the device functions
>       in the guest)
>    3) Host power off testing: Power off the device from the host, verify
>       that the device is unplugged from the guest as part of the poweroff
>    4) Guest power off testing: Power off the device from within the guest,
>       verify that the device is unusable in the guest,
>       power the device back on within the guest and verify that the device
>       is once again usable.
>    5) Guest reboot testing: (create a VM with a vfio-pci device,
>       verify the device is in working condition, reboot the guest,
>       verify that the device is still usable after reboot)
> 
> [Regression Potential]
> 
>  * The regression potential is moderate, since the code is upstream
>    for quite a while and already enabled in jammy.
> 
>  * The general way on using passthrough has not changed, with this
>    change (config option) it's now just possible to passthrough
>    zPCI on top.
> 
>  * CCW devices are not affected.
> 
>  * And this is s390x-specific anyway, so no other architectures are affected.
> 
> [Other]
> 
>  * The enablement of the kernel config option is the same for L, M and U/N,
>    but I submitted separate patches due to slightly different contexts.
> 
>  * v2: - renamed patch to kernel option name
>        - toggled existing option from n to y
>        - reworked patch description
> 
> Frank Heimes (1):
>   UBUNTU: [Config] CONFIG_VFIO_PCI_ZDEV_KVM=y
> 
>  debian.master/config/annotations | 3 +++
>  1 file changed, 3 insertions(+)
> 
> -- 
> 2.25.1
> 
> 
> -- 
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> kernel-team at lists.ubuntu.com
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Acked-by: Manuel Diewald <manuel.diewald at canonical.com>
-- 
 Manuel