On 10/22/2010 12:06 PM, Jeremy Fitzhardinge wrote:
>
> Well, if you want to map a normal memory page, you'd use, say,
> pfn_pte(pfn, PAGE_KERNEL) to generate the pte. The pfn is a
> domain-local pseudo-physical address. When it ends up in
> xen_make_pte(), it will translate the the pfn into a machine-global mfn
> to generate a pte_t which can be inserted into a pagetable. (And when
> that pagetable starts being used as such, Xen will validate that the mfn
> is actually one the domain is allowed to address.)
>
> However, if you're doing an ioremap(), then the mapped address is a
> hardware one. In that case, we construct the pte with
> pfn_pte(device_pfn, PAGE_KERNEL_IO), which sets the _PAGE_IOMAP flag in
> the pte flags. When it gets to xen_make_pte(), it sees _PAGE_IOMAP and
> constructs a pte_t containing the literal untranslated device_pfn
> (really an mfn). (And again, Xen will check that the domain has access
> to that mfn before allowing the mapping to be used.)
>
When you're doing an ioremap(), then the mapped address is *both* a PFN
and an MFN, right? So why do your need a flag? That is the part I
don't get...
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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