Problem with remap_page_range on IA32 with more than 4GB RAM

[John Fusco <fusco_john@yahoo.com>]

I have a problem and I would like some comments on how to fix it.

I have a custom PCI-X device installed in an IA32 system.  The device 
expects to see a flat contiguous address space on the host, from which 
it reads and sends its data.  The technique I used is right out of the 
O'Reilly Device Drivers book, which is to hide memory from the kernel 
with the 'mem=YYY' boot parameter.  I then provide a mmap method to map 
the contiguous (hidden) memory into user space via a call to 
'remap_page_range'.

Everything worked great until we decided that we needed to install 6GB 
in this system.  The problem is that remap_page_range() uses an unsigned 
long as the parameter for a physical address.  On IA32, an unsigned long 
is 32-bits, but the IA32 is capable of addressing well over 4GB of RAM.  
So physical addresses on IA32 must be larger than 32 bits.

I chose to work around this by patching the kernel.  I changed the 
unsigned long parameters used for physical address in mm/memory.c to 
'dma64_addr_t'.  This seems to work and I don't see any holes in the 
approach, but I would appreciate any comments (or better solutions).

I can post the patch here if anyone would like to see it.  It seems that 
Linux could use a unique typedef for a physical address.  Right now I 
think dma64_addr_t fits the bill.

Thanks,
John
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