remap kernel static memory to user space

From: Eduardo Cruz
Date: Wed Mar 20 2013 - 16:06:43 EST


I'm trying to remap some kernel static memory to user space using
For that, I wrote a module that initializes a device, which later I
use mknod, etc.

When I allocate the memory with kmalloc, everything works: (where
user_space_shared was allocated with kmalloc)

if ((ret = remap_pfn_range(vma, vma->vm_start,
virt_to_phys(user_space_shared) >> PAGE_SHIFT, length,
vma->vm_page_prot)) < 0)

In the application in user space:
kstc = mmap(0, sizeof(user_space_shared_t), PROT_READ|PROT_WRITE,

With user_space_shared allocated using kmalloc, it is working.
The application is able to read the data I wrote in the kernel module.

However, when I define and allocate that var in arch/ia64/mm/fault.c:

unsigned char user_space_shared[ sizeof(user_space_shared_t) +
PAGE_SIZE ] __attribute__((aligned(PAGE_SIZE)));

And access that var from the module:

extern unsigned char user_space_shared[ sizeof(user_space_shared_t) +

There is no error message, but I can't read the contents i wrote
inside the kernel module from the application.

Your help would be appreciated.

I am taking care of page offsets/boundaries.
I'm using kernel 2.6.32 for ia64.

Eduardo Henrique Molina da Cruz
PhD student
Parallel and Distributed Processing Group
Federal University of Rio Grande do Sul (UFRGS)
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