From: Michael S. Tsirkin <mst@redhat.com>
Sent: Tuesday, October 31, 2023 5:02 AM

On Mon, Oct 30, 2023 at 06:10:06PM +0000, Parav Pandit wrote:

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From: Michael S. Tsirkin <mst@redhat.com>
Sent: Monday, October 30, 2023 9:29 PM On Mon, Oct 30, 2023 at
03:51:40PM +0000, Parav Pandit wrote:

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From: Michael S. Tsirkin <mst@redhat.com>
Sent: Monday, October 30, 2023 1:53 AM

On Sun, Oct 29, 2023 at 05:59:45PM +0200, Yishai Hadas wrote:

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From: Feng Liu <redacted>

Introduce support for the admin virtqueue. By negotiating
VIRTIO_F_ADMIN_VQ feature, driver detects capability and
creates one administration virtqueue. Administration virtqueue
implementation in virtio pci generic layer, enables multiple
types of upper layer drivers such as vfio, net, blk to utilize it.

Signed-off-by: Feng Liu <redacted>
Reviewed-by: Parav Pandit <redacted>
Reviewed-by: Jiri Pirko <redacted>
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
---
 drivers/virtio/virtio.c                | 37 ++++++++++++++--
 drivers/virtio/virtio_pci_common.c     |  3 ++
 drivers/virtio/virtio_pci_common.h     | 15 ++++++-
 drivers/virtio/virtio_pci_modern.c     | 61

+++++++++++++++++++++++++-

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 drivers/virtio/virtio_pci_modern_dev.c | 18 ++++++++
 include/linux/virtio_config.h          |  4 ++
 include/linux/virtio_pci_modern.h      |  5 +++
 7 files changed, 137 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c

index
3893dc29eb26..f4080692b351 100644

--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c

@@ -302,9 +302,15 @@ static int virtio_dev_probe(struct device *_d)
 	if (err)
 		goto err;

+	if (dev->config->create_avq) {
+		err = dev->config->create_avq(dev);
+		if (err)
+			goto err;
+	}
+
 	err = drv->probe(dev);
 	if (err)
-		goto err;
+		goto err_probe;

 	/* If probe didn't do it, mark device DRIVER_OK ourselves. */
 	if (!(dev->config->get_status(dev) &

VIRTIO_CONFIG_S_DRIVER_OK))

Hmm I am not all that happy that we are just creating avq

unconditionally.

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Can't we do it on demand to avoid wasting resources if no one uses it?

Virtio queues must be enabled before driver_ok as we discussed in

F_DYNAMIC bit exercise.

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So creating AQ when first legacy command is invoked, would be too late.

Well we didn't release the spec with AQ so I am pretty sure there
are no devices using the feature. Do we want to already make an
exception for AQ and allow creating AQs after DRIVER_OK even without

F_DYNAMIC?

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No. it would abuse the init time config registers for the dynamic things like

this.

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For flow filters and others there is need for dynamic q creation with multiple

physical address anyway.

That seems like a completely unrelated issue.

It isn't.
Driver requirements are:
1. Driver needs to dynamically create vqs
2. Sometimes this VQ needs to have multiple physical addresses
3. Driver needs to create them after driver is fully running, past the bootstrap stage using tiny config registers

Device requirements are:
1. Not to keep growing 64K VQs *(8+8+8) bytes of address registers + enable bit
2. Ability to return appropriate error code when fail to create queue
3. Above #2

Users of this new infrastructure are eth tx,rx queues, flow filter queues, aq, blk rq per cpu.
AQs are just one of those.
When a generic infrastructure for this will be built in the spec as we started that, all above use cases will be handled.

quoted

So creating virtqueues dynamically using a generic scheme is desired with

new feature bit.

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