From: William Lee Irwin III <wli@holomorphy.com>
To: John Fusco <fusco_john@yahoo.com>
Cc: linux-mm@kvack.org
Subject: Re: Problem with remap_page_range on IA32 with more than 4GB RAM
Date: Thu, 23 Sep 2004 16:27:27 -0700 [thread overview]
Message-ID: <20040923232727.GK9106@holomorphy.com> (raw)
In-Reply-To: <41535AAE.6090700@yahoo.com>
On Thu, Sep 23, 2004 at 06:22:22PM -0500, John Fusco wrote:
> 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.
I wrote a patch that made it take a pfn at some point. I suppose I
could respin that while renaming the function to remap_pfn_range() or
otherwise fiddle with whatever whoever complained about.
-- wli
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next prev parent reply other threads:[~2004-09-23 23:27 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-23 23:22 John Fusco
2004-09-23 23:27 ` William Lee Irwin III [this message]
2004-09-24 3:22 ` Is there a node-affinity memory allocation benchmark? Annie
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