Re: [PATCH v2 19/24] vdpa: make sure set_features in invoked for legacy

On Wed, Aug 05, 2020 at 02:14:07PM +0800, Jason Wang wrote:

On 2020/8/4 上午5:00, Michael S. Tsirkin wrote:

quoted

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.

I wonder whether it's easier to just support modern device?

Thanks

Well hardware vendors are I think interested in supporting legacy
guests. Limiting vdpa to modern only would make it uncompetitive.

quoted

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 */

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