Re: Why get_user_pages fails?

On Mon, 30 Jun 2008 19:32:41 +0000
"Pan, Weimin" <weimin.pan@xxxxxx> wrote:

I booted the kernel and set "mem=512M" and then mmapped the physical
memory above 512M to user space and got the user space virtual
address for that memory. When I passed that address to my driver to
do direct IO. The get_user_pages() in my driver fails. I found that
this is due to the VM_IO and VM_PFNMAP are set. Does that mean the
page structures are not built when I mmapped physical memory to user
space (using remap_pfn_range())?

Do I have a way to solve this problem? How can I map the physical
memory to user space virtual address and can pass this address to my
driver to do direct IO by using get_user_pages() function?

In this situation, you already know where the memory sits in physical
space, and there's no point in trying to pin it. So a call to
get_user_pages() is entirely unnecessary. You're bypassing the Linux
VM, so bypass it entirely.

However, this whole scheme seems a little...baroque. Why are you doing
things this way? As always in such cases, posting your code can enable
others to help you find the right solution to your problem.

jon
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