Re: [RFC 1/2] xen/mm: Clarify the granularity for each Frame Number

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 05/08/15 13:36, Julien Grall wrote:
> On 05/08/15 12:40, Andrew Cooper wrote:
>> I think a section about granularity is worthwhile, but probably a
>> separate paragraph.  I think it is also worth keeping Xen's idea of
>> memory all at 4K, and in cases where 64K is in use, require appropriate
>> alignment in the parameter.
> Which would confuse the reader because PFN which, based on the
> description, is the OS Frame Number. This frame will always be in the
> granularity of the OS.

"A linear idea of a guest physical address space." says nothing about
the OS.  It is purely a Xen concept, as described here.

>
> So we need to introduce the concept of in each definition. This patch
> makes clear that MFN and GFN is always 4KB and PFN may vary.

Is (or rather will) a 4K dom0 able to make 4K mappings of a 64K domU? 
How is a 64K dom0 expected to make mappings of a 4K domU?

The primary use of "pfn" in Xen is logdirty tracking (which ARM doesn't
have yet), but will have to be set at the minimum granularity of the
toolstack domain, domU and the logdirty ABI which currently is assumed
to be 4K pages because of its x86 heritage.

~Andrew