Re: [PATCH vfio 03/11] virtio-pci: Introduce admin virtqueue

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On 2023-09-26 p.m.3:23, Feng Liu via Virtualization wrote:
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On 2023-09-21 a.m.9:57, Michael S. Tsirkin wrote:
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On Thu, Sep 21, 2023 at 03:40:32PM +0300, Yishai Hadas wrote:
From: Feng Liu <feliu@xxxxxxxxxx>

  drivers/virtio/virtio_pci_modern_avq.c | 65 ++++++++++++++++++++++++++

if you have a .c file without a .h file you know there's something
fishy. Just add this inside drivers/virtio/virtio_pci_modern.c ?

Will do.

+struct virtio_avq {

admin_vq would be better. and this is pci specific yes? so virtio_pci_

Will do.

+     struct virtio_avq *admin;

and this could be thinkably admin_vq.

Will do.

  /* If driver didn't advertise the feature, it will never appear. */
diff --git a/include/linux/virtio_pci_modern.h b/include/linux/virtio_pci_modern.h
index 067ac1d789bc..f6cb13d858fd 100644
--- a/include/linux/virtio_pci_modern.h
+++ b/include/linux/virtio_pci_modern.h
@@ -10,6 +10,9 @@ struct virtio_pci_modern_common_cfg {

       __le16 queue_notify_data;       /* read-write */
       __le16 queue_reset;             /* read-write */
+     __le16 admin_queue_index;       /* read-only */
+     __le16 admin_queue_num;         /* read-only */

actually there's a problem

         mdev->common = vp_modern_map_capability(mdev, common,
                                       sizeof(struct virtio_pci_common_cfg), 4,                                        0, sizeof(struct virtio_pci_common_cfg),
                                       NULL, NULL);

extending this structure means some calls will start failing on
existing devices.

even more of an ouch, when we added queue_notify_data and queue_reset we
also possibly broke some devices. well hopefully not since no one
reported failures but we really need to fix that.

Hi Michael

I didn’t see the fail in vp_modern_map_capability(), and
vp_modern_map_capability() only read and map pci memory. The length of
the memory mapping will increase as the struct virtio_pci_common_cfg
increases. No errors are seen.

And according to the existing code, new pci configuration space members
can only be added in struct virtio_pci_modern_common_cfg.

Every single entry added here is protected by feature bit, there is no
bug AFAIK.

Could you help to explain it more detail?  Where and why it will fall if
we add new member in struct virtio_pci_modern_common_cfg.

Hi, Michael
	Any comments about this?

  struct virtio_pci_modern_device {

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