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    SubjectRe: [PATCH v3 1/1] s390: virtio: let arch accept devices without IOMMU feature
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    On 2020-06-19 11:20, Cornelia Huck wrote:
    > On Thu, 18 Jun 2020 00:29:56 +0200
    > Halil Pasic <pasic@linux.ibm.com> wrote:
    >
    >> On Wed, 17 Jun 2020 12:43:57 +0200
    >> Pierre Morel <pmorel@linux.ibm.com> wrote:
    ...
    >>
    >> But since this can be rewritten any time, let's go with the option
    >> people already agree with, instead of more discussion.
    >
    > Yes, there's nothing wrong with the patch as-is.
    >
    > Acked-by: Cornelia Huck <cohuck@redhat.com>

    Thanks,


    >
    > Which tree should this go through? Virtio? s390? >
    >>
    >> Just another question. Do we want this backported? Do we need cc stable?
    >
    > It does change behaviour of virtio-ccw devices; but then, it only
    > fences off configurations that would not have worked anyway.
    > Distributions should probably pick this; but I do not consider it
    > strictly a "fix" (more a mitigation for broken configurations), so I'm
    > not sure whether stable applies.
    >
    >> [..]
    >>
    >>
    >>> int virtio_finalize_features(struct virtio_device *dev)
    >>> {
    >>> int ret = dev->config->finalize_features(dev);
    >>> @@ -179,6 +194,13 @@ int virtio_finalize_features(struct virtio_device *dev)
    >>> if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
    >>> return 0;
    >>>
    >>> + if (arch_needs_virtio_iommu_platform(dev) &&
    >>> + !virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
    >>> + dev_warn(&dev->dev,
    >>> + "virtio: device must provide VIRTIO_F_IOMMU_PLATFORM\n");
    >>
    >> I'm not sure, divulging the current Linux name of this feature bit is a
    >> good idea, but if everybody else is fine with this, I don't care that
    >
    > Not sure if that feature name will ever change, as it is exported in
    > headers. At most, we might want to add the new ACCESS_PLATFORM define
    > and keep the old one, but that would still mean some churn.
    >
    >> much. An alternative would be:
    >> "virtio: device falsely claims to have full access to the memory,
    >> aborting the device"
    >
    > "virtio: device does not work with limited memory access" ?
    >
    > But no issue with keeping the current message.
    >

    If it is OK, I would like to specify that the arch is responsible to
    accept or not the device.
    The reason why the device is not accepted without IOMMU_PLATFORM is arch
    specific.

    Regards,
    Pierre

    --
    Pierre Morel
    IBM Lab Boeblingen

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