Xen users - Apr 2007 - ioremap failure on highmem reserved memory with RHEL 5 Xen Linux

Hello ,
    I have installed RHEL 5 on a Intel Core Duo processor based board. It
has 1 GB of physical memory. I  have a driver which uses the memory reserved
at the top of the high memory. Well this driver worked fine on all the
previous versions of RHEL/FC and also with RHEL 5 with virtualization
disabled. But  with virtualization enabled , the ioremap to the memory
reserved at the top of high mem( usin highmem command line option) fails.
On digging into the kernel code, I found out that the check if the memory
address which I am passing to the ioremap is falling in the low memory
region is failing. I rechecked if this is the case by printing the system
information which confirmed that the address is not in the low mem. Also
another thing which i noticed was that the high mem start which is normally
set to 896MB is shifted to 728MB which confused me even further. Further
looking into the ioremap code, the check is failing due to the fact that the
mfn_to_local_pfn is giving a value which is less that max pfn . I was under
the assumptions that the mfn should be equal for the pfn for Dom0.
Is there anything I need to do in the driver specific to Xen to access the
reserved memory.I would really appreciate if anybody can help me out on this
as I am new to Xen.

regards,
Girish


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