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Reply-To: <imran.badr@cavium.com>
From: "Imran Badr" <imran.badr@cavium.com>
To: <linux-kernel@vger.kernel.org>
Subject: Calculating kernel logical address ..
Date: Thu, 5 Sep 2002 20:34:07 -0700
Message-ID: <00d301c25556$4290f5e0$9e10a8c0@IMRANPC>
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Hi,

I need help to correctly calculate kernel logical address for a user pointer
which I mmaped from device driver. In mmap() file operation, I allocate some
memory using kmalloc() and call :

remap_page_range(vma->vm_start,
virt_to_phys((void *)(Uint32)kmalloc_buffer),
size,
PAGE_SHARED);

after reserving all pages and doing some other stuff. Now when I get a user
pointer and I need to calculate correspoding kernel logical address, I use
following code:

adr = user_address;
pgd_offset(current->mm, adr);

if (!pgd_none(*pgd)) {
	pmd = pmd_offset(pgd, adr);
	if (!pmd_none(*pmd)) {
		ptep = pte_offset(pmd, adr);
		pte = *ptep;
		if(pte_present(pte)) {
			kaddr  = (unsigned long) page_address(pte_page(pte));
			kaddr |= (adr & (PAGE_SIZE - 1));
		}
	}
}

Will this code always give me correct kernel logical address?

I will really appreciate any guidance.

Thanks,
Imran.


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