linux-kernel - Re: [RFC PATCH] vfio/type1: Do not support IOMMUs that allow bypass

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Date:	Fri, 16 Oct 2015 16:03:11 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [RFC PATCH] vfio/type1: Do not support IOMMUs that allow bypass

Hi Alex,
On 10/15/2015 10:52 PM, Alex Williamson wrote:
> We can only provide isolation if DMA is forced through the IOMMU
> aperture.  Don't allow type1 to be used if this is not the case.
> 
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
> 
> Eric, I see a number of IOMMU drivers enable this, do the ones you
> care about for ARM set geometry.force_aperture?  Thanks,
I am currently using arm-smmu.c. I don't see force_aperture being set.

Best Regards

Eric
> 
> Alex
> 
>  drivers/vfio/vfio_iommu_type1.c |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 57d8c37..6afa9d4 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -728,6 +728,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>  	struct vfio_group *group, *g;
>  	struct vfio_domain *domain, *d;
>  	struct bus_type *bus = NULL;
> +	struct iommu_domain_geometry geometry;
>  	int ret;
>  
>  	mutex_lock(&iommu->lock);
> @@ -762,6 +763,17 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>  		goto out_free;
>  	}
>  
> +	/*
> +	 * If a domain does not force DMA within the aperture, devices are not
> +	 * isolated and type1 is not an appropriate IOMMU model.
> +	 */
> +	ret = iommu_domain_get_attr(domain->domain,
> +				    DOMAIN_ATTR_GEOMETRY, &geometry);
> +	if (ret || !geometry.force_aperture) {
> +		ret = -EPERM;
> +		goto out_domain;
> +	}
> +
>  	if (iommu->nesting) {
>  		int attr = 1;
>  
> 

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