linux-kernel - Re: [PATCH] s390: protvirt: virtio: Refuse device without IOMMU

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Date:   Wed, 10 Jun 2020 17:27:01 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     linux-kernel@...r.kernel.org, pasic@...ux.ibm.com,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, mst@...hat.com,
        jasowang@...hat.com, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] s390: protvirt: virtio: Refuse device without IOMMU



On 2020-06-10 16:53, Cornelia Huck wrote:
> On Wed, 10 Jun 2020 16:37:55 +0200
> Pierre Morel <pmorel@...ux.ibm.com> wrote:
> 
>> On 2020-06-10 15:24, Cornelia Huck wrote:
>>> On Wed, 10 Jun 2020 15:11:51 +0200
>>> Pierre Morel <pmorel@...ux.ibm.com> wrote:
>>>    
>>>> Protected Virtualisation protects the memory of the guest and
>>>> do not allow a the host to access all of its memory.
>>>>
>>>> Let's refuse a VIRTIO device which does not use IOMMU
>>>> protected access.
>>>>
>>>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>>>> ---
>>>>    drivers/s390/virtio/virtio_ccw.c | 5 +++++
>>>>    1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
>>>> index 5730572b52cd..06ffbc96587a 100644
>>>> --- a/drivers/s390/virtio/virtio_ccw.c
>>>> +++ b/drivers/s390/virtio/virtio_ccw.c
>>>> @@ -986,6 +986,11 @@ static void virtio_ccw_set_status(struct virtio_device *vdev, u8 status)
>>>>    	if (!ccw)
>>>>    		return;
>>>>    
>>>> +	/* Protected Virtualisation guest needs IOMMU */
>>>> +	if (is_prot_virt_guest() &&
>>>> +	    !__virtio_test_bit(vdev, VIRTIO_F_IOMMU_PLATFORM))
>>>> +			status &= ~VIRTIO_CONFIG_S_FEATURES_OK;
>>>> +
>>>
>>> set_status seems like an odd place to look at features; shouldn't that
>>> rather be done in finalize_features?
>>
>> Right, looks better to me too.
>> What about:
>>
>>
>>
>> diff --git a/drivers/s390/virtio/virtio_ccw.c
>> b/drivers/s390/virtio/virtio_ccw.c
>> index 06ffbc96587a..227676297ea0 100644
>> --- a/drivers/s390/virtio/virtio_ccw.c
>> +++ b/drivers/s390/virtio/virtio_ccw.c
>> @@ -833,6 +833,11 @@ static int virtio_ccw_finalize_features(struct
>> virtio_device *vdev)
>>                   ret = -ENOMEM;
>>                   goto out_free;
>>           }
>> +
>> +       if (is_prot_virt_guest() &&
>> +           !__virtio_test_bit(vdev, VIRTIO_F_IOMMU_PLATFORM))
> 
> Add a comment, and (maybe) a message?
> 
> Otherwise, I think this is fine, as it should fail the probe, which is
> what we want.

yes right a message is needed.
and I extend a little the comment I had before.
thanks

Regards,
Pierre

-- 
Pierre Morel
IBM Lab Boeblingen