linux-kernel - Re: remap kernel static memory to user space

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Date:	Thu, 21 Mar 2013 20:45:54 -0300
From:	Eduardo Cruz <eduardohmdacruz@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: remap kernel static memory to user space

Please, anyone knows how to solve this problem?

2013/3/20 Eduardo Cruz <eduardohmdacruz@...il.com>:
> Hello.
>
> I'm trying to remap some kernel static memory to user space using
> remap_pfn_range.
> 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,
> MAP_SHARED| MAP_LOCKED, fd, 0);
>
> 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)));
> EXPORT_SYMBOL(user_space_shared);
>
> And access that var from the module:
>
> extern unsigned char user_space_shared[ sizeof(user_space_shared_t) +
> PAGE_SIZE ];
>
> 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.
>
> ps:
> 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)



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