Re: [RFC PATCH 1/2] xen: introduce arch_iommu_grant_(un)map_page

[Julien Grall <julien.grall@linaro.org>]

Hi Ian,

On 16/07/14 16:56, Ian Campbell wrote:
> On Tue, 2014-07-08 at 16:53 +0100, Stefano Stabellini wrote:
>> +int arch_iommu_grant_map_page(struct domain *d, unsigned long frame,
>> +                              unsigned flags)
>> +{
>> +    p2m_type_t t;
>> +
>> +    /* Grant mappings can be used for DMA requests. The dev_bus_addr returned by
>> +     * the hypercall is the MFN (not the IPA). For device protected by
>> +     * an IOMMU, Xen needs to add a 1:1 mapping in the domain p2m to
>> +     * allow DMA request to work.
>> +     * This is only valid when the domain is directed mapped.
>> +     */
>> +    BUG_ON(!is_domain_direct_mapped(d));
>
> What stops a non-1:1 guest from trying to map a grant reference and
> ending up here?

The function is protected by gnttab_need_iommu_mapping which check if 
the domain use direct mapping for the memory.

Regards,

-- 
Julien Grall