[linux-sh:03343] Re: Howto convert from process virtual (linear address) to physical address?

On Fri, Oct 08, 2004 at 05:40:32PM +0100, Alex Bennee wrote:
> Now I'm probably just lost because I haven't got my head fully wrapped
> around the multi-level page tables but this is what I've got:
> 
>     do {
> 	pgd_t *pgd;
> 	pmd_t *pmd;
> 	pte_t *ptep, pte;
> 	struct page *the_page;
> 	unsigned long phys_addr;
> 	
>  	get_user(addr, start_addr);
> 	start_addr++;
> 
>         pgd = pgd_offset(tsk->mm, addr);
>         if (pgd_none(*pgd) || pgd_bad(*pgd))
> 	    goto out;
>  
>         pmd = pmd_offset(pgd, addr);
>         if (pmd_none(*pmd) || pmd_bad(*pmd))
> 	    goto out;
>  
>         ptep = pte_offset(pmd, addr);
>         if (!ptep)
> 	    goto out;
>  
>         pte = *ptep;
> 
> 	the_page = pte_page(pte);
> 	phys_addr = page_to_phys(the_page)+(addr&PAGE_MASK);

This looks problematic.

What about:

	phys_addr = pte_val(*ptep) & PTE_PHYS_MASK;

> Any idea where I'm going wrong? A pointer to code that actually needs to
> convert from user-space linear address to actual physical address would
> be cool if anyone can point me to one.
> 
The closest you will probably get is copy/clear_user_page(), but that
probably won't help you much.

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