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

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Date:   Wed, 10 Jun 2020 15:24:31 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Pierre Morel <pmorel@...ux.ibm.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 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?

>  	/* Write the status to the host. */
>  	vcdev->dma_area->status = status;
>  	ccw->cmd_code = CCW_CMD_WRITE_STATUS;