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

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Date:   Thu, 2 Jul 2020 15:03:51 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org, pasic@...ux.ibm.com,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, jasowang@...hat.com,
        kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, thomas.lendacky@....com,
        david@...son.dropbear.id.au, linuxram@...ibm.com,
        heiko.carstens@...ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v3 1/1] s390: virtio: let arch accept devices without
 IOMMU feature



On 2020-06-29 18:05, Cornelia Huck wrote:
> On Mon, 29 Jun 2020 11:57:14 -0400
> "Michael S. Tsirkin" <mst@...hat.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@...ux.ibm.com>
>>> Acked-by: Jason Wang <jasowang@...hat.com>
>>> Acked-by: Christian Borntraeger <borntraeger@...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.
> 

Yes, clearly, I will add this.

Thanks,
Pierre

-- 
Pierre Morel
IBM Lab Boeblingen