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

[Julien Grall <julien.grall@xxxxxxxxxx>]

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

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