Re: [PATCH v3 1/1] s390: virtio: let arch accept devices without IOMMU feature

Pierre Morel
2020-07-06T15:03:56Z

On 2020-07-06 16:33, Cornelia Huck wrote:
> On Mon, 6 Jul 2020 15:37:37 +0200
> Pierre Morel <pmorel@linux.ibm.com> wrote:
>
>> On 2020-07-02 15:03, Pierre Morel wrote:
>>>
>>>
>>> On 2020-06-29 18:05, Cornelia Huck wrote:
>>>> On Mon, 29 Jun 2020 11:57:14 -0400
>>>> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>>>>
>>>>> On Wed, Jun 17, 2020 at 12:43:57PM +0200, Pierre Morel wrote:
>>>>>> An architecture protecting the guest memory against unauthorized host
>>>>>> access may want to enforce VIRTIO I/O device protection through the
>>>>>> use of VIRTIO_F_IOMMU_PLATFORM.
>>>>>>
>>>>>> Let's give a chance to the architecture to accept or not devices
>>>>>> without VIRTIO_F_IOMMU_PLATFORM.
>>>>>>
>>>>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>>>>>> Acked-by: Jason Wang <jasowang@redhat.com>
>>>>>> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
>>>>>> ---
>>>>>>   arch/s390/mm/init.c     |  6 ++++++
>>>>>>   drivers/virtio/virtio.c | 22 ++++++++++++++++++++++
>>>>>>   include/linux/virtio.h  |  2 ++
>>>>>>   3 files changed, 30 insertions(+)
>>>>
>>>>>> @@ -179,6 +194,13 @@ int virtio_finalize_features(struct
>>>>>> virtio_device *dev)
>>>>>>       if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
>>>>>>           return 0;
>>>>>> +    if (arch_needs_virtio_iommu_platform(dev) &&
>>>>>> +        !virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
>>>>>> +        dev_warn(&dev->dev,
>>>>>> +             "virtio: device must provide VIRTIO_F_IOMMU_PLATFORM\n");
>>>>>> +        return -ENODEV;
>>>>>> +    }
>>>>>> +
>>>>>>       virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
>>>>>>       status = dev->config->get_status(dev);
>>>>>>       if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
>>>>>
>>>>> Well don't you need to check it *before* VIRTIO_F_VERSION_1, not after?
>>>>
>>>> But it's only available with VERSION_1 anyway, isn't it? So it probably
>>>> also needs to fail when this feature is needed if VERSION_1 has not been
>>>> negotiated, I think.
>>
>>
>> would be something like:
>>
>> - if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
>> - return 0;
>> + if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
>> + ret = arch_accept_virtio_features(dev);
>> + if (ret)
>> + dev_warn(&dev->dev,
>> + "virtio: device must provide
>> VIRTIO_F_VERSION_1\n");
>> + return ret;
>> + }
>
> That looks wrong; I think we want to validate in all cases. What about:
>
> ret = arch_accept_virtio_features(dev); // this can include checking for
> // older or newer features
> if (ret)
> // assume that the arch callback moaned already
> return ret;
>
> if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
> return 0;
>
> // do the virtio-1 only FEATURES_OK dance

hum, you are right, I was too focused on keeping my simple
arch_accept_virtio_features() function unchanged.
It must be more general.

>
>>
>>
>> just a thought on the function name:
>> It becomes more general than just IOMMU_PLATFORM related.
>>
>> What do you think of:
>>
>> arch_accept_virtio_features()
>
> Or maybe arch_validate_virtio_features()?

OK validated.

Thanks,
Pierre

--
Pierre Morel
IBM Lab Boeblingen