Xen/ARM API issue (page size)

[Elliott Mitchell <ehem+xen@xxxxxxx>]

Hopefully I'm not about to show the limits of my knowledge...

Quite a few values passed to Xen via hypercalls include a page number.
This makes sense as that maps to the hardware.  Problem is, I cannot help
but notice aarch64 allows for 4KB, 16KB and 64KB pages.

I don't know how flexible aarch64 is.  I don't know whether an aarch64
core can support multiple page sizes.  My tentative reading of
information seemed to suggest a typical aarch64 core /could/ allow
multiple page sizes.

What happens if a system (and Xen) is setup to support 64KB pages, but a
particular domain has been built strictly with 4KB page support?

What if a particular domain wanted to use 64KB pages (4KB being too
granular), but Xen was set to use 4KB pages?

What if a system had two domains which were set for different page sizes,
but the two needed to interact?


Then you have things like VCPUOP_register_vcpu_info.  The structure is
setup as mfn and offset.  With the /actual/ page size being used there,
it is troublesome.  Several places might work better if pure 64-bit
addresses were used, but with alignment requirements specified.

Then there is a question of what happens when we get a core which has
more than 64 physical address bits (seems a few years off, but for a long
time 32 seemed high).


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