Issue with shared information page on Xen/ARM 4.17

[Elliott Mitchell <ehem+xen@xxxxxxx>]

I'm trying to get FreeBSD/ARM operational on Xen/ARM.  Current issue is
the changes with the handling of the shared information page appear to
have broken things for me.

With a pre-4.17 build of Xen/ARM things worked fine.  Yet with a build
of the 4.17 release, mapping the shared information page doesn't work.

I'm using Tianocore as the first stage loader.  This continues to work
fine.  The build is using tag "edk2-stable202211", commit fff6d81270.
While Tianocore does map the shared information page, my reading of their
source is that it properly unmaps the page and therefore shouldn't cause
trouble.

Notes on the actual call is gpfn was 0x0000000000040072.  This is outside
the recommended address range, but my understanding is this is supposed
to be okay.

The return code is -16, which is EBUSY.

Ideas?

The obvious spot for EBUSY is from already having the shared information
page mapped.  Issue is I'm pretty sure it isn't mapped.

Did the policy change and now the shared information page *must* be
mapped within the recommended address ranges?

Is it a problem to map the shared information page at one address.  Unmap
it, then map it at another address?


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