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    Subject[PATCH v2 19/24] vdpa: make sure set_features in invoked for legacy
    Some legacy guests just assume features are 0 after reset.
    We detect that config space is accessed before features are
    set and set features to 0 automatically.
    Note: some legacy guests might not even access config space, if this is
    reported in the field we might need to catch a kick to handle these.

    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    ---
    drivers/vdpa/vdpa.c | 1 +
    include/linux/vdpa.h | 34 ++++++++++++++++++++++++++++++++++
    2 files changed, 35 insertions(+)

    diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
    index de211ef3738c..7105265e4793 100644
    --- a/drivers/vdpa/vdpa.c
    +++ b/drivers/vdpa/vdpa.c
    @@ -96,6 +96,7 @@ struct vdpa_device *__vdpa_alloc_device(struct device *parent,
    vdev->dev.release = vdpa_release_dev;
    vdev->index = err;
    vdev->config = config;
    + vdev->features_valid = false;

    err = dev_set_name(&vdev->dev, "vdpa%u", vdev->index);
    if (err)
    diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
    index 239db794357c..29b8296f1414 100644
    --- a/include/linux/vdpa.h
    +++ b/include/linux/vdpa.h
    @@ -33,12 +33,14 @@ struct vdpa_notification_area {
    * @dma_dev: the actual device that is performing DMA
    * @config: the configuration ops for this device.
    * @index: device index
    + * @features_valid: were features initialized? for legacy guests
    */
    struct vdpa_device {
    struct device dev;
    struct device *dma_dev;
    const struct vdpa_config_ops *config;
    unsigned int index;
    + bool features_valid;
    };

    /**
    @@ -266,4 +268,36 @@ static inline struct device *vdpa_get_dma_dev(struct vdpa_device *vdev)
    {
    return vdev->dma_dev;
    }
    +
    +static inline void vdpa_reset(struct vdpa_device *vdev)
    +{
    + const struct vdpa_config_ops *ops = vdev->config;
    +
    + vdev->features_valid = false;
    + ops->set_status(vdev, 0);
    +}
    +
    +static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features)
    +{
    + const struct vdpa_config_ops *ops = vdev->config;
    +
    + vdev->features_valid = true;
    + return ops->set_features(vdev, features);
    +}
    +
    +
    +static inline void vdpa_get_config(struct vdpa_device *vdev, unsigned offset,
    + void *buf, unsigned int len)
    +{
    + const struct vdpa_config_ops *ops = vdev->config;
    +
    + /*
    + * Config accesses aren't supposed to trigger before features are set.
    + * If it does happen we assume a legacy guest.
    + */
    + if (!vdev->features_valid)
    + vdpa_set_features(vdev, 0);
    + ops->get_config(vdev, offset, buf, len);
    +}
    +
    #endif /* _LINUX_VDPA_H */
    --
    MST
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