[Xen-devel] Feature Request : dummy paddings for mapping memory holes in privcmd

[Guanglin Xu <mzguanglin@xxxxxxxxx>]

Hi Andres, David, Konrad and all,

A couple weeks ago, I posted a thread named "Bug: privcmd failure in
mmaping 160+ pages", but finally I found that it is not the fact. It's
just a feature of Xen - denying to map memory holes.

However, as a developer of high efficient VMI (Virtual Machine Introspection)
applications, I appreciate hypervisor to map the whole guest memory
for us.

While Xen has been providing mmap_foreign_range() API by libxc and
privcmd for a long time, it denies to map if the requested page range
includes memory holes, such as page 160 - 191 legacy video buffer, VGA
reserved memory, PCI hole, MMIO hole, etc. (see
http://techfiles.de/dmelanchthon/files/memory_hole.pdf ).

Maybe you would ask, "what the hell do you want dummy memory holes?!"
It is because VMI applications are almost about memory searching where
both the probing of derived separate memory regions and processing on
them can slow it down a lot.

In fact, we have recently added such feature for KVM hypervisor.
However, we are not familiar with Xen. So we hope Xen community can
help.

Thanks,

Guanglin

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