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

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Date:   Wed, 10 Jun 2020 16:37:55 +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 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))
+               return -EIO;
+
         /* Give virtio_ring a chance to accept features. */
         vring_transport_features(vdev);



Thanks,

Regards,
Pierre

-- 
Pierre Morel
IBM Lab Boeblingen