On Wed, Sep 15, 2021 at 11:18:06AM +0800, Jason Wang wrote:

On Tue, Sep 14, 2021 at 8:58 PM Michael S. Tsirkin [off-list ref] wrote:

quoted

On Tue, Sep 14, 2021 at 08:24:51PM +0800, Wu Zongyong wrote:

quoted

This new attribute advertises whether the vdpa device is legacy or not.
Users can pick right virtqueue size if the vdpa device is legacy which
doesn't support to change virtqueue size.

Signed-off-by: Wu Zongyong <redacted>

So if we are bothering with legacy,

I think we'd better not. I guess the following may work:

1) disable the driver on BE host
2) present VERSION_1 with ACCESS_PLATFORM in get_features()
3) extend the management to advertise max_queue_size and
min_queue_size, for ENI they are the same so management layer knows it
needs to set the queue_size correctly during launching qemu

Thoughts?

Thanks

There are other subtle differences such as header size without
mergeable buffers for net.

quoted

I think there are
several things to do when building the interface
- support transitional devices, that is allow userspace
  to tell device it's in legacy mode
- support reporting/setting supporting endian-ness

quoted

---
 drivers/vdpa/vdpa.c          | 6 ++++++
 drivers/virtio/virtio_vdpa.c | 7 ++++++-
 include/uapi/linux/vdpa.h    | 1 +
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
index 1dc121a07a93..533d7f589eee 100644
--- a/drivers/vdpa/vdpa.c
+++ b/drivers/vdpa/vdpa.c

@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/vdpa.h>
 #include <uapi/linux/vdpa.h>
+#include <uapi/linux/virtio_config.h>
 #include <net/genetlink.h>
 #include <linux/mod_devicetable.h>

@@ -494,6 +495,7 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
      u16 max_vq_size;
      u32 device_id;
      u32 vendor_id;
+     u64 features;
      void *hdr;
      int err;

@@ -508,6 +510,7 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
      device_id = vdev->config->get_device_id(vdev);
      vendor_id = vdev->config->get_vendor_id(vdev);
      max_vq_size = vdev->config->get_vq_num_max(vdev);
+     features = vdev->config->get_features(vdev);

      err = -EMSGSIZE;
      if (nla_put_string(msg, VDPA_ATTR_DEV_NAME, dev_name(&vdev->dev)))

@@ -520,6 +523,9 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
              goto msg_err;
      if (nla_put_u16(msg, VDPA_ATTR_DEV_MAX_VQ_SIZE, max_vq_size))
              goto msg_err;
+     if (features & BIT_ULL(VIRTIO_F_VERSION_1) &&
+         nla_put_flag(msg, VDPA_ATTR_DEV_VERSION_1))
+             goto msg_err;

      genlmsg_end(msg, hdr);
      return 0;

diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
index 72eaef2caeb1..1cba957c4cdc 100644
--- a/drivers/virtio/virtio_vdpa.c
+++ b/drivers/virtio/virtio_vdpa.c

@@ -7,6 +7,7 @@
  *
  */

+#include "linux/virtio_config.h"
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/device.h>

@@ -145,6 +146,7 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
      /* Assume split virtqueue, switch to packed if necessary */
      struct vdpa_vq_state state = {0};
      unsigned long flags;
+     bool may_reduce_num = false;
      u32 align, num;
      int err;

@@ -169,10 +171,13 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
              goto error_new_virtqueue;
      }

+     if (ops->get_features(vdpa) & BIT_ULL(VIRTIO_F_VERSION_1))
+             may_reduce_num = true;
+
      /* Create the vring */
      align = ops->get_vq_align(vdpa);
      vq = vring_create_virtqueue(index, num, align, vdev,
-                                 true, true, ctx,
+                                 true, may_reduce_num, ctx,
                                  virtio_vdpa_notify, callback, name);
      if (!vq) {
              err = -ENOMEM;

diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
index 66a41e4ec163..ce0b74276a5b 100644
--- a/include/uapi/linux/vdpa.h
+++ b/include/uapi/linux/vdpa.h

@@ -32,6 +32,7 @@ enum vdpa_attr {
      VDPA_ATTR_DEV_VENDOR_ID,                /* u32 */
      VDPA_ATTR_DEV_MAX_VQS,                  /* u32 */
      VDPA_ATTR_DEV_MAX_VQ_SIZE,              /* u16 */
+     VDPA_ATTR_DEV_VERSION_1,                /* flag */

      /* new attributes must be added above here */
      VDPA_ATTR_MAX,
--

2.31.1

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