[Xen-devel] [PATCH RFC 0/2] Linux: possible ixes for mapping high MMIO regions

[David Vrabel <david.vrabel@xxxxxxxxxx>]

This a possible fix for the problems with mapping high MMIO regions in
certain cases (e.g., the RDMA drivers) as not all mappers were
specifing the _PAGE_IOMAP which meant no valid MFN could be found and
the resulting PTE would be marked as not present, causing subsequent
faults.

It assumes that anything that isn't RAM (whether ballooned out or not)
is an I/O region and thus should be 1:1 in the p2m.  Ballooned frames
are still marked as missing in the p2m as before.

As a follow on, mfn_to_pfn() is (hopefully) extended to do the right
thing with such an MFN.  This means the Xen-specific _PAGE_IOMAP PTE
flag can be removed,

This series is posted as an early RFC in the hope that is an
acceptable approach.  It has only seen the bare minimum of smoke
testing (my test dom0 didn't explode). In particular, I've not
actually tested it with a device with a high MMIO.

David


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