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Message-ID: <96a236da-7165-b59b-e013-919554fb1ac4@linux.ibm.com>
Date: Mon, 15 Jun 2020 13:49:54 +0200
From: Pierre Morel <pmorel@...ux.ibm.com>
To: Halil Pasic <pasic@...ux.ibm.com>, Jason Wang <jasowang@...hat.com>
Cc: linux-kernel@...r.kernel.org, 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 12:37, Halil Pasic wrote:
> On Mon, 15 Jun 2020 11:01:55 +0800
> Jason Wang <jasowang@...hat.com> wrote:
>
>>> hum, in between I found another way which seems to me much better:
>>>
>>> We already have the force_dma_unencrypted() function available which
>>> AFAIU is what we want for encrypted memory protection and is already
>>> used by power and x86 SEV/SME in a way that seems AFAIU compatible
>>> with our problem.
>>>
>>> Even DMA and IOMMU are different things, I think they should be used
>>> together in our case.
>>>
>>> What do you think?
>>>
>>> The patch would then be something like:
>>>
>>> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
>>> index a977e32a88f2..53476d5bbe35 100644
>>> --- a/drivers/virtio/virtio.c
>>> +++ b/drivers/virtio/virtio.c
>>> @@ -4,6 +4,7 @@
>>> #include <linux/virtio_config.h>
>>> #include <linux/module.h>
>>> #include <linux/idr.h>
>>> +#include <linux/dma-direct.h>
>>> #include <uapi/linux/virtio_ids.h>
>>>
>>> /* Unique numbering for virtio devices. */
>>> @@ -179,6 +180,10 @@ int virtio_finalize_features(struct virtio_device
>>> *dev)
>>> if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
>>> return 0;
>>>
>>> + if (force_dma_unencrypted(&dev->dev) &&
>>> + !virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM))
>>> + return -EIO;
>>> +
>>> virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
>>> status = dev->config->get_status(dev);
>>> if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
>>
>>
>> I think this can work but need to listen from Michael
>
> I don't think Christoph Hellwig will like force_dma_unencrypted()
> in virtio code:
> https://lkml.org/lkml/2020/2/20/630
>
> Regards,
> Halil
>
OK, then back to the first idea.
Thanks,
Pierre
--
Pierre Morel
IBM Lab Boeblingen
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