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SubjectRe: [PATCH] vfio/mtty: Enforce available_instances
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On 6/29/2021 12:26 AM, Alex Williamson wrote:
> On Mon, 28 Jun 2021 23:19:54 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
>
>> On 6/26/2021 2:56 AM, Alex Williamson wrote:
>>> The sample mtty mdev driver doesn't actually enforce the number of
>>> device instances it claims are available. Implement this properly.
>>>
>>> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
>>> ---
>>>
>>> Applies to vfio next branch + Jason's atomic conversion
>>>
>>
>>
>> Does this need to be on top of Jason's patch?
>
> Yes, see immediately above.
>
>> Patch to use mdev_used_ports is reverted here, can it be changed from
>> mdev_devices_list to mdev_avail_ports atomic variable?
>
> It doesn't revert Jason's change, it builds on it. The patches could
> we squashed, but there's no bug in Jason's patch that we're trying to
> avoid exposing, so I don't see why we'd do that.
>

'Squashed' is the correct word that 'revert', my bad.

>> Change here to use atomic variable looks good to me.
>>
>> Reviewed by: Kirti Wankhede <kwankhede@nvidia.com>
>
> Thanks! It was Jason's patch[1] that converted to use an atomic
> though, so I'm slightly confused if this R-b is for the patch below,
> Jason's patch, or both. Thanks,

I liked 'mdev_avail_ports' approach than 'mdev_used_ports' approach
here. This R-b is for below patch.

Thanks,
Kirti

>
> Alex
>
> [1]https://lore.kernel.org/kvm/0-v1-0bc56b362ca7+62-mtty_used_ports_jgg@nvidia.com/
>
>>> samples/vfio-mdev/mtty.c | 22 ++++++++++++++++------
>>> 1 file changed, 16 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
>>> index ffbaf07a17ea..8b26fecc4afe 100644
>>> --- a/samples/vfio-mdev/mtty.c
>>> +++ b/samples/vfio-mdev/mtty.c
>>> @@ -144,7 +144,7 @@ struct mdev_state {
>>> int nr_ports;
>>> };
>>>
>>> -static atomic_t mdev_used_ports;
>>> +static atomic_t mdev_avail_ports = ATOMIC_INIT(MAX_MTTYS);
>>>
>>> static const struct file_operations vd_fops = {
>>> .owner = THIS_MODULE,
>>> @@ -707,11 +707,20 @@ static int mtty_probe(struct mdev_device *mdev)
>>> {
>>> struct mdev_state *mdev_state;
>>> int nr_ports = mdev_get_type_group_id(mdev) + 1;
>>> + int avail_ports = atomic_read(&mdev_avail_ports);
>>> int ret;
>>>
>>> + do {
>>> + if (avail_ports < nr_ports)
>>> + return -ENOSPC;
>>> + } while (!atomic_try_cmpxchg(&mdev_avail_ports,
>>> + &avail_ports, avail_ports - nr_ports));
>>> +
>>> mdev_state = kzalloc(sizeof(struct mdev_state), GFP_KERNEL);
>>> - if (mdev_state == NULL)
>>> + if (mdev_state == NULL) {
>>> + atomic_add(nr_ports, &mdev_avail_ports);
>>> return -ENOMEM;
>>> + }
>>>
>>> vfio_init_group_dev(&mdev_state->vdev, &mdev->dev, &mtty_dev_ops);
>>>
>>> @@ -724,6 +733,7 @@ static int mtty_probe(struct mdev_device *mdev)
>>>
>>> if (mdev_state->vconfig == NULL) {
>>> kfree(mdev_state);
>>> + atomic_add(nr_ports, &mdev_avail_ports);
>>> return -ENOMEM;
>>> }
>>>
>>> @@ -735,9 +745,9 @@ static int mtty_probe(struct mdev_device *mdev)
>>> ret = vfio_register_group_dev(&mdev_state->vdev);
>>> if (ret) {
>>> kfree(mdev_state);
>>> + atomic_add(nr_ports, &mdev_avail_ports);
>>> return ret;
>>> }
>>> - atomic_add(mdev_state->nr_ports, &mdev_used_ports);
>>>
>>> dev_set_drvdata(&mdev->dev, mdev_state);
>>> return 0;
>>> @@ -746,12 +756,13 @@ static int mtty_probe(struct mdev_device *mdev)
>>> static void mtty_remove(struct mdev_device *mdev)
>>> {
>>> struct mdev_state *mdev_state = dev_get_drvdata(&mdev->dev);
>>> + int nr_ports = mdev_state->nr_ports;
>>>
>>> - atomic_sub(mdev_state->nr_ports, &mdev_used_ports);
>>> vfio_unregister_group_dev(&mdev_state->vdev);
>>>
>>> kfree(mdev_state->vconfig);
>>> kfree(mdev_state);
>>> + atomic_add(nr_ports, &mdev_avail_ports);
>>> }
>>>
>>> static int mtty_reset(struct mdev_state *mdev_state)
>>> @@ -1271,8 +1282,7 @@ static ssize_t available_instances_show(struct mdev_type *mtype,
>>> {
>>> unsigned int ports = mtype_get_type_group_id(mtype) + 1;
>>>
>>> - return sprintf(buf, "%d\n",
>>> - (MAX_MTTYS - atomic_read(&mdev_used_ports)) / ports);
>>> + return sprintf(buf, "%d\n", atomic_read(&mdev_avail_ports) / ports);
>>> }
>>>
>>> static MDEV_TYPE_ATTR_RO(available_instances);
>>>
>>>
>>
>

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