Date:   Fri, 13 Jan 2023 11:40:39 +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 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?

Also, will set_vq_ready(0) after DRIVER_OK result in queue deletion?

>
> 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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