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

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Date:   Mon, 15 Jun 2020 13:50:56 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Jason Wang <jasowang@...hat.com>, linux-kernel@...r.kernel.org
Cc:     pasic@...ux.ibm.com, borntraeger@...ibm.com, frankja@...ux.ibm.com,
        mst@...hat.com, cohuck@...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 2020-06-15 05:01, Jason Wang wrote:
> 
> On 2020/6/12 下午7:38, Pierre Morel wrote:
>>
>>
>> On 2020-06-12 11:21, Pierre Morel wrote:
>>>
>>>
>>> On 2020-06-11 05:10, Jason Wang wrote:
>>>>
>>>> On 2020/6/10 下午9:11, Pierre Morel 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;
>>>>> +
>>>>>       /* Write the status to the host. */
>>>>>       vcdev->dma_area->status = status;
>>>>>       ccw->cmd_code = CCW_CMD_WRITE_STATUS;
>>>>
>>>>
>>>> I wonder whether we need move it to virtio core instead of ccw.
>>>>
>>>> I think the other memory protection technologies may suffer from 
>>>> this as well.
>>>>
>>>> Thanks
>>>>
>>>
>>>
>>> What would you think of the following, also taking into account 
>>> Connie's comment on where the test should be done:
>>>
>>> - declare a weak function in virtio.c code, returning that memory 
>>> protection is not in use.
>>>
>>> - overwrite the function in the arch code
>>>
>>> - call this function inside core virtio_finalize_features() and if 
>>> required fail if the device don't have VIRTIO_F_IOMMU_PLATFORM.
> 
> 
> I think this is fine.
> 

Thanks,
I try this.

Regards,
Pierre




-- 
Pierre Morel
IBM Lab Boeblingen