Re: [Xen-devel] [PATCH 5/7] public / x86: introduce __HYPERCALL_iommu_op

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Paul Durrant
> Sent: Monday, February 12, 2018 6:47 PM
> 
> This patch introduces the boilerplate for a new hypercall to allow a
> domain to control IOMMU mappings for its own pages.
> Whilst there is duplication of code between the native and compat entry
> points which appears ripe for some form of combination, I think it is
> better to maintain the separation as-is because the compat entry point
> will necessarily gain complexity in subsequent patches.
> 
> NOTE: This hypercall is only implemented for x86 and is currently
>       restricted by XSM to dom0 since it could be used to cause IOMMU
>       faults which may bring down a host.
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
[...]
> +
> +
> +static bool can_control_iommu(void)
> +{
> +    struct domain *currd = current->domain;
> +
> +    /*
> +     * IOMMU mappings cannot be manipulated if:
> +     * - the IOMMU is not enabled or,
> +     * - the IOMMU is passed through or,
> +     * - shared EPT configured or,
> +     * - Xen is maintaining an identity map.

"for dom0"

> +     */
> +    if ( !iommu_enabled || iommu_passthrough ||
> +         iommu_use_hap_pt(currd) || need_iommu(currd) )

I guess it's clearer to directly check iommu_dom0_strict here

> +        return false;
> +
> +    return true;
> +}


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