Re: [Xen-devel] [PATCH v9 2/2] xen/arm: grant: Add another entry to map MFN 1:1 in dom0 p2m

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-05-27 at 14:51 +0100, Jan Beulich wrote:
> >>> On 27.05.14 at 13:11, <julien.grall@xxxxxxxxxx> wrote:
> > Grant mappings can be used for DMA requests. Currently the dev_bus_addr 
> > returned
> > by the hypercall is the MFN (not the IPA). Guest expects to be able the 
> > returned
> > address for DMA. When the device is protected by IOMMU the request will 
> > fail.
> > Therefore, we have to add 1:1 mapping in the domain p2m to allow DMA request
> > to work.
> > 
> > This is valid because DOM0 has its memory mapped 1:1 and therefore we know
> > that RAM and devices cannot clash.
> > 
> > If the guest only owns protected device, the return dev_bus_addr should be 
> > an
> > IPA. This will allow us to remove safely the 1:1 mapping and make grant 
> > mapping
> > works correctly in the guest. For now, this is not addressed by this patch.
> > 
> > The grant mapping code does the reference counting on every MFN and will
> > call iommu_{map,unmap}_page when necessary. This was already handle for x86
> > PV guests, so we can reuse the same code path for ARM guest.
> > 
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> 
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> on the common and x86 changes, provided you change ...

I'm going to apply and make these two changes as I go.

> 
> > --- a/xen/include/asm-arm/grant_table.h
> > +++ b/xen/include/asm-arm/grant_table.h
> > @@ -33,6 +33,9 @@ static inline int replace_grant_supported(void)
> >      ( ((i >= nr_grant_frames(d->grant_table)) &&                         \
> >       (i < max_nr_grant_frames)) ? 0 : (d->arch.grant_table_gpfn[i]))
> >  
> > +#define gnttab_need_iommu_mapping(d)                    \
> > +    (is_domain_direct_mapped(d) && need_iommu(ld))
> 
> ... from "ld" to "d" here and ...
> 
> > --- a/xen/include/asm-x86/grant_table.h
> > +++ b/xen/include/asm-x86/grant_table.h
> > @@ -65,6 +65,9 @@ static inline void gnttab_clear_flag(unsigned int nr, 
> > uint16_t *st)
> >  /* Done implicitly when page tables are destroyed. */
> >  #define gnttab_release_host_mappings(domain) ( 
> > paging_mode_external(domain) )
> >  
> > +#define gnttab_need_iommu_mapping(d)                \
> > +    (!paging_mode_translate(d) && need_iommu(ld))
> 
> ... here.
> 
> Jan
> 



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