memory mapping of vmalloc

memory mapping of vmalloc

[Prakash Bhurke]

Hi ,

  I am facing a problem -- memory mapping of proc
entry into user space using mmap syscall.
  I have written a module which creates a proc entry &
provides read, write, mmap, etc.
  Normal read, write etc file operation works, but
mmap is not working.
  I am trying to map a vmalloc kernel buffer to user
space using remap_page_range(). In my module, this
function returns success if we call mmap() from user
space, but i can not access content of vmalloc buffer
from user space. Pointer returned by mmap() syscall
seems pointing to other memory page which contains
zeros. I am using linux 2.6.10 kernel on Pentium 4
system.

here is code of module_mmap();
static inline unsigned long kvirt_to_pa(unsigned long
adr)
{
	unsigned long kva, ret;

	kva = (unsigned long)
page_address(vmalloc_to_page((void *)adr));
	kva |= adr & (PAGE_SIZE-1); /* restore the offset */
	ret = __pa(kva);
	return ret;
}

static int module_mmap(struct file *file, struct
vm_area_struct *vma)
{
	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
	unsigned long len = vma->vm_end - vma->vm_start;
	unsigned long pos = (unsigned long) test_tsc +
offset;

	printk(KERN_INFO "PROCINFO : in mmap started, length
= %ld\n", len);

	if (!tscinfo)
		return -ENODEV;

	if ((offset + len) > PAGE_ALIGN(sizeof(sizeof(struct
test_tsc_info)))))
		return -ENXIO;

	if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) ==
(VM_SHARED|VM_WRITE)) {
		printk("PROCINFO : in mmap attempt to write to
mapping\n");
		return -EPERM;
	}

	vma->vm_flags |= VM_SHM | VM_LOCKED ;

	if (remap_pfn_range(vma, vma->vm_start,
kvirt_to_pa(pos) >> PAGE_SHIFT, \
			     len, vma->vm_page_prot)) {
		printk(KERN_INFO "PROCINFO : in mmap remap_pfn_range
returns error\n");
		return -EAGAIN;
	}

	printk(KERN_INFO "PROCINFO : in mmap ret 0 end\n");

	return 0;
}

>From user space program i mapping kernel memory like
this
proc_fd = open("/proc/"PROC_ENTRY_FILENAME, O_RDONLY);
mem_base = mmap(NULL, sizeof(struct test_tsc_info),
PROT_READ, MAP_SHARED, proc_fd, 0);

Please let me know what wrong thing i m doing.

Regards,
Prakash.



		
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Re: memory mapping of vmalloc

[Hugh Dickins]

On Tue, 1 Mar 2005, Prakash Bhurke wrote:
>   I am trying to map a vmalloc kernel buffer to user
> space using remap_page_range(). In my module, this
> function returns success if we call mmap() from user
> space, but i can not access content of vmalloc buffer
> from user space. Pointer returned by mmap() syscall
> seems pointing to other memory page which contains
> zeros. I am using linux 2.6.10 kernel on Pentium 4
> system.

Look for "rvmalloc" in various drivers in the kernel source tree:
you must SetPageReserved before remap_pfn_range (or remap_page_range)
agrees to map the page, and ClearPageReserved before freeing after.

Hugh

Re: memory mapping of vmalloc

[Prakash Bhurke]

Hi  Hugh,

   rvmallaoc is working.
   Very Very Thanks.

Regards,
Prakash

--- Hugh Dickins <hugh@veritas.com> wrote:

> On Tue, 1 Mar 2005, Prakash Bhurke wrote:
> >   I am trying to map a vmalloc kernel buffer to
> user
> > space using remap_page_range(). In my module, this
> > function returns success if we call mmap() from
> user
> > space, but i can not access content of vmalloc
> buffer
> > from user space. Pointer returned by mmap()
> syscall
> > seems pointing to other memory page which contains
> > zeros. I am using linux 2.6.10 kernel on Pentium 4
> > system.
> 
> Look for "rvmalloc" in various drivers in the kernel
> source tree:
> you must SetPageReserved before remap_pfn_range (or
> remap_page_range)
> agrees to map the page, and ClearPageReserved before
> freeing after.
> 
> Hugh
> -
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