Date:   Fri, 13 Jan 2023 12:03:06 +0530
From:   Gautam Dawar <gdawar@....com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Gautam Dawar <gautam.dawar@....com>, linux-net-drivers@....com,
        netdev@...r.kernel.org, eperezma@...hat.com, tanuj.kamde@....com,
        Koushik.Dutta@....com, harpreet.anand@....com,
        Edward Cree <ecree.xilinx@...il.com>,
        Martin Habets <habetsm.xilinx@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 08/11] sfc: implement device status related vdpa
 config operations


On 1/13/23 11:50, Jason Wang wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
>
>
> On Fri, Jan 13, 2023 at 2:11 PM Gautam Dawar <gdawar@....com> wrote:
>>
>> On 1/13/23 09:58, Jason Wang wrote:
>>> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
>>>
>>>
>>> On Wed, Jan 11, 2023 at 2:36 PM Jason Wang <jasowang@...hat.com> wrote:
>>>> On Mon, Jan 9, 2023 at 6:21 PM Gautam Dawar <gdawar@....com> wrote:
>>>>> On 12/14/22 12:15, Jason Wang wrote:
>>>>>> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
>>>>>>
>>>>>>
>>>>>> On Wed, Dec 7, 2022 at 10:57 PM Gautam Dawar <gautam.dawar@....com> wrote:
>>>>>>> vDPA config opertions to handle get/set device status and device
>>>>>>> reset have been implemented.
>>>>>>>
>>>>>>> Signed-off-by: Gautam Dawar <gautam.dawar@....com>
>>>>>>> ---
>>>>>>>     drivers/net/ethernet/sfc/ef100_vdpa.c     |   7 +-
>>>>>>>     drivers/net/ethernet/sfc/ef100_vdpa.h     |   1 +
>>>>>>>     drivers/net/ethernet/sfc/ef100_vdpa_ops.c | 133 ++++++++++++++++++++++
>>>>>>>     3 files changed, 140 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/drivers/net/ethernet/sfc/ef100_vdpa.c b/drivers/net/ethernet/sfc/ef100_vdpa.c
>>>>>>> index 04d64bfe3c93..80bca281a748 100644
>>>>>>> --- a/drivers/net/ethernet/sfc/ef100_vdpa.c
>>>>>>> +++ b/drivers/net/ethernet/sfc/ef100_vdpa.c
>>>>>>> @@ -225,9 +225,14 @@ static int vdpa_allocate_vis(struct efx_nic *efx, unsigned int *allocated_vis)
>>>>>>>
>>>>>>>     static void ef100_vdpa_delete(struct efx_nic *efx)
>>>>>>>     {
>>>>>>> +       struct vdpa_device *vdpa_dev;
>>>>>>> +
>>>>>>>            if (efx->vdpa_nic) {
>>>>>>> +               vdpa_dev = &efx->vdpa_nic->vdpa_dev;
>>>>>>> +               ef100_vdpa_reset(vdpa_dev);
>>>>>> Any reason we need to reset during delete?
>>>>> ef100_reset_vdpa_device() does the necessary clean-up including freeing
>>>>> irqs, deleting filters and deleting the vrings which is required while
>>>>> removing the vdpa device or unloading the driver.
>>>> That's fine but the name might be a little bit confusing since vDPA
>>>> reset is not necessary here.
>>>>
>>>>>>> +
>>>>>>>                    /* replace with _vdpa_unregister_device later */
>>>>>>> -               put_device(&efx->vdpa_nic->vdpa_dev.dev);
>>>>>>> +               put_device(&vdpa_dev->dev);
>>>>>>>                    efx->vdpa_nic = NULL;
>>>>>>>            }
>>>>>>>            efx_mcdi_free_vis(efx);
>>>>>>> diff --git a/drivers/net/ethernet/sfc/ef100_vdpa.h b/drivers/net/ethernet/sfc/ef100_vdpa.h
>>>>>>> index a33edd6dda12..1b0bbba88154 100644
>>>>>>> --- a/drivers/net/ethernet/sfc/ef100_vdpa.h
>>>>>>> +++ b/drivers/net/ethernet/sfc/ef100_vdpa.h
>>>>>>> @@ -186,6 +186,7 @@ int ef100_vdpa_add_filter(struct ef100_vdpa_nic *vdpa_nic,
>>>>>>>                              enum ef100_vdpa_mac_filter_type type);
>>>>>>>     int ef100_vdpa_irq_vectors_alloc(struct pci_dev *pci_dev, u16 nvqs);
>>>>>>>     void ef100_vdpa_irq_vectors_free(void *data);
>>>>>>> +int ef100_vdpa_reset(struct vdpa_device *vdev);
>>>>>>>
>>>>>>>     static inline bool efx_vdpa_is_little_endian(struct ef100_vdpa_nic *vdpa_nic)
>>>>>>>     {
>>>>>>> diff --git a/drivers/net/ethernet/sfc/ef100_vdpa_ops.c b/drivers/net/ethernet/sfc/ef100_vdpa_ops.c
>>>>>>> index 132ddb4a647b..718b67f6da90 100644
>>>>>>> --- a/drivers/net/ethernet/sfc/ef100_vdpa_ops.c
>>>>>>> +++ b/drivers/net/ethernet/sfc/ef100_vdpa_ops.c
>>>>>>> @@ -251,6 +251,62 @@ static bool is_qid_invalid(struct ef100_vdpa_nic *vdpa_nic, u16 idx,
>>>>>>>            return false;
>>>>>>>     }
>>>>>>>
>>>>>>> +static void ef100_reset_vdpa_device(struct ef100_vdpa_nic *vdpa_nic)
>>>>>>> +{
>>>>>>> +       int i;
>>>>>>> +
>>>>>>> +       WARN_ON(!mutex_is_locked(&vdpa_nic->lock));
>>>>>>> +
>>>>>>> +       if (!vdpa_nic->status)
>>>>>>> +               return;
>>>>>>> +
>>>>>>> +       vdpa_nic->vdpa_state = EF100_VDPA_STATE_INITIALIZED;
>>>>>>> +       vdpa_nic->status = 0;
>>>>>>> +       vdpa_nic->features = 0;
>>>>>>> +       for (i = 0; i < (vdpa_nic->max_queue_pairs * 2); i++)
>>>>>>> +               reset_vring(vdpa_nic, i);
>>>>>>> +}
>>>>>>> +
>>>>>>> +/* May be called under the rtnl lock */
>>>>>>> +int ef100_vdpa_reset(struct vdpa_device *vdev)
>>>>>>> +{
>>>>>>> +       struct ef100_vdpa_nic *vdpa_nic = get_vdpa_nic(vdev);
>>>>>>> +
>>>>>>> +       /* vdpa device can be deleted anytime but the bar_config
>>>>>>> +        * could still be vdpa and hence efx->state would be STATE_VDPA.
>>>>>>> +        * Accordingly, ensure vdpa device exists before reset handling
>>>>>>> +        */
>>>>>>> +       if (!vdpa_nic)
>>>>>>> +               return -ENODEV;
>>>>>>> +
>>>>>>> +       mutex_lock(&vdpa_nic->lock);
>>>>>>> +       ef100_reset_vdpa_device(vdpa_nic);
>>>>>>> +       mutex_unlock(&vdpa_nic->lock);
>>>>>>> +       return 0;
>>>>>>> +}
>>>>>>> +
>>>>>>> +static int start_vdpa_device(struct ef100_vdpa_nic *vdpa_nic)
>>>>>>> +{
>>>>>>> +       int rc = 0;
>>>>>>> +       int i, j;
>>>>>>> +
>>>>>>> +       for (i = 0; i < (vdpa_nic->max_queue_pairs * 2); i++) {
>>>>>>> +               if (can_create_vring(vdpa_nic, i)) {
>>>>>>> +                       rc = create_vring(vdpa_nic, i);
>>>>>> So I think we can safely remove the create_vring() in set_vq_ready()
>>>>>> since it's undefined behaviour if set_vq_ready() is called after
>>>>>> DRIVER_OK.
>>>>> Is this (undefined) behavior documented in the virtio spec?
>>>> This part is kind of tricky:
>>>>
>>>> PCI transport has a queue_enable field. And recently,
>>>> VIRTIO_F_RING_RESET was introduced. Let's start without that first:
>>>>
>>>> In
>>>>
>>>> 4.1.4.3.2 Driver Requirements: Common configuration structure layout
>>>>
>>>> It said:
>>>>
>>>> "The driver MUST configure the other virtqueue fields before enabling
>>>> the virtqueue with queue_enable."
>>>>
>>>> and
>>>>
>>>> "The driver MUST NOT write a 0 to queue_enable."
>>>>
>>>> My understanding is that:
>>>>
>>>> 1) Write 0 is forbidden
>>>> 2) Write 1 after DRIVER_OK is undefined behaviour (or need to clarify)
>>>>
>>>> With VIRTIO_F_RING_RESET is negotiated:
>>>>
>>>> "
>>>> If VIRTIO_F_RING_RESET has been negotiated, after the driver writes 1
>>>> to queue_reset to reset the queue, the driver MUST NOT consider queue
>>>> reset to be complete until it reads back 0 in queue_reset. The driver
>>>> MAY re-enable the queue by writing 1 to queue_enable after ensuring
>>>> that other virtqueue fields have been set up correctly. The driver MAY
>>>> set driver-writeable queue configuration values to different values
>>>> than those that were used before the queue reset. (see 2.6.1).
>>>> "
>>>>
>>>> Write 1 to queue_enable after DRIVER_OK and after the queue is reset is allowed.
>>>>
>>>> Thanks
>>> Btw, I just realized that we need to stick to the current behaviour,
>>> that is to say, to allow set_vq_ready() to be called after DRIVER_OK.
>> So, both set_vq_ready() and DRIVER_OK are required for vring creation
>> and their order doesn't matter. Is that correct?
> Yes.
>
>> Also, will set_vq_ready(0) after DRIVER_OK result in queue deletion?
> I think it should be treated as suspended or stopped. Since the device
> should survive from kicking the vq even if the driver does
> set_vq_ready(0).
Ok. Is it expected that a queue restart (set_vq_ready(0) followed by 
set_vq_ready(1)) will start the queue from the last queue configuration 
when VIRTIO_F_RING_RESET isn't negotiated?
>
> Thanks
>
>>> It is needed for the cvq trap and migration for control virtqueue:
>>>
>>> https://www.mail-archive.com/qemu-devel@nongnu.org/msg931491.html
>>>
>>> Thanks
>>>
>>>
>>>>> If so, can
>>>>> you please point me to the section of virtio spec that calls this order
>>>>> (set_vq_ready() after setting DRIVER_OK) undefined? Is it just that the
>>>>> queue can't be enabled after DRIVER_OK or the reverse (disabling the
>>>>> queue) after DRIVER_OK is not allowed?
>>>>>>> +                       if (rc)
>>>>>>> +                               goto clear_vring;
>>>>>>> +               }
>>>>>>> +       }
>>>>>>> +       vdpa_nic->vdpa_state = EF100_VDPA_STATE_STARTED;
>>>>>>> +       return rc;
>>>>>>> +
>>>>>>> +clear_vring:
>>>>>>> +       for (j = 0; j < i; j++)
>>>>>>> +               if (vdpa_nic->vring[j].vring_created)
>>>>>>> +                       delete_vring(vdpa_nic, j);
>>>>>>> +       return rc;
>>>>>>> +}
>>>>>>> +
>>>>>>>     static int ef100_vdpa_set_vq_address(struct vdpa_device *vdev,
>>>>>>>                                         u16 idx, u64 desc_area, u64 driver_area,
>>>>>>>                                         u64 device_area)
>>>>>>> @@ -568,6 +624,80 @@ static u32 ef100_vdpa_get_vendor_id(struct vdpa_device *vdev)
>>>>>>>            return EF100_VDPA_VENDOR_ID;
>>>>>>>     }
>>>>>>>
>>>>>>> +static u8 ef100_vdpa_get_status(struct vdpa_device *vdev)
>>>>>>> +{
>>>>>>> +       struct ef100_vdpa_nic *vdpa_nic = get_vdpa_nic(vdev);
>>>>>>> +       u8 status;
>>>>>>> +
>>>>>>> +       mutex_lock(&vdpa_nic->lock);
>>>>>>> +       status = vdpa_nic->status;
>>>>>>> +       mutex_unlock(&vdpa_nic->lock);
>>>>>>> +       return status;
>>>>>>> +}
>>>>>>> +
>>>>>>> +static void ef100_vdpa_set_status(struct vdpa_device *vdev, u8 status)
>>>>>>> +{
>>>>>>> +       struct ef100_vdpa_nic *vdpa_nic = get_vdpa_nic(vdev);
>>>>>>> +       u8 new_status;
>>>>>>> +       int rc;
>>>>>>> +
>>>>>>> +       mutex_lock(&vdpa_nic->lock);
>>>>>>> +       if (!status) {
>>>>>>> +               dev_info(&vdev->dev,
>>>>>>> +                        "%s: Status received is 0. Device reset being done\n",
>>>>>>> +                        __func__);
>>>>>>> +               ef100_reset_vdpa_device(vdpa_nic);
>>>>>>> +               goto unlock_return;
>>>>>>> +       }
>>>>>>> +       new_status = status & ~vdpa_nic->status;
>>>>>>> +       if (new_status == 0) {
>>>>>>> +               dev_info(&vdev->dev,
>>>>>>> +                        "%s: New status same as current status\n", __func__);
>>>>>>> +               goto unlock_return;
>>>>>>> +       }
>>>>>>> +       if (new_status & VIRTIO_CONFIG_S_FAILED) {
>>>>>>> +               ef100_reset_vdpa_device(vdpa_nic);
>>>>>>> +               goto unlock_return;
>>>>>>> +       }
>>>>>>> +
>>>>>>> +       if (new_status & VIRTIO_CONFIG_S_ACKNOWLEDGE &&
>>>>>>> +           vdpa_nic->vdpa_state == EF100_VDPA_STATE_INITIALIZED) {
>>>>>> As replied before, I think there's no need to check
>>>>>> EF100_VDPA_STATE_INITIALIZED, otherwise it could be a bug somewhere.
>>>>> Ok. Will remove the check against EF100_VDPA_STATE_INITIALIZED.
>>>>>>> +               vdpa_nic->status |= VIRTIO_CONFIG_S_ACKNOWLEDGE;
>>>>>>> +               new_status &= ~VIRTIO_CONFIG_S_ACKNOWLEDGE;
>>>>>>> +       }
>>>>>>> +       if (new_status & VIRTIO_CONFIG_S_DRIVER &&
>>>>>>> +           vdpa_nic->vdpa_state == EF100_VDPA_STATE_INITIALIZED) {
>>>>>>> +               vdpa_nic->status |= VIRTIO_CONFIG_S_DRIVER;
>>>>>>> +               new_status &= ~VIRTIO_CONFIG_S_DRIVER;
>>>>>>> +       }
>>>>>>> +       if (new_status & VIRTIO_CONFIG_S_FEATURES_OK &&
>>>>>>> +           vdpa_nic->vdpa_state == EF100_VDPA_STATE_INITIALIZED) {
>>>>>>> +               vdpa_nic->status |= VIRTIO_CONFIG_S_FEATURES_OK;
>>>>>>> +               vdpa_nic->vdpa_state = EF100_VDPA_STATE_NEGOTIATED;
>>>>>> I think we can simply map EF100_VDPA_STATE_NEGOTIATED to
>>>>>> VIRTIO_CONFIG_S_FEATURES_OK.
>>>>>>
>>>>>> E.g the code doesn't fail the feature negotiation by clearing the
>>>>>> VIRTIO_CONFIG_S_FEATURES_OK when ef100_vdpa_set_driver_feature fails?
>>>>> Ok.
>>>>>> Thanks
>>>>> Regards,
>>>>>
>>>>> Gautam
>>>>>

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