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SubjectRe: pte_page

On Wed, 30 May 2001 wrote:

> I use the 'pgt_offset', 'pmd_offset', 'pte_offset' and 'pte_page'
> inside a module to get the physical address of a user space virtual
> address. The physical address returned by 'pte_page' is not page
> aligned whereas the virtual address was page aligned. Can somebody
> tell me the reason?

__pa(page_address(pte_page(pte))) is the address you want. [or
pte_val(*pte) & (PAGE_SIZE-1) on x86 but this is platform-dependent.]

> Also, can i use these functions to get the physical address of a
> kernel virtual address using init_mm?

nope. Eg. on x86 these functions only walk normal 4K page pagetables, they
do not walk 4MB pages correctly. (which are set up on pentiums and better
CPUs, unless mem=nopentium is specified.)

a kernel virtual address can be decoded by simply doing __pa(kaddr). If
the page is a highmem page [and you have the struct page pointer] then you
can do [(page-mem_map) << PAGE_SHIFT] to get the physical address, but
only on systems where mem_map[] starts at physical address 0.


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